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Infectious coryza (IC) is an acute upper respiratory disease of chicken caused by Avibacterium (A.) paragallinarum. This disease results in an increased culling rate in meat chicken and a marked decrease in egg production (10% to more than 40%) in laying and breeding hens. Vaccines were first used against IC and effectively controlled the disease. Nanotechnology provides an excellent way to develop a new generation of vaccines. NPs have been widely used in vaccine design as adjuvants and antigen delivery vehicles and as antibacterial agents; thus, they can be used as inactivators for bacterial culture. In this research, the antibacterial effects of several nanoparticles (NPs), such as silicon dioxide with chitosan (SiO 2 -CS), oleoyl-chitosan (O.CS), silicon dioxide (SiO 2 ), and iron oxide (Fe 3 O 4 ), on A. paragallinarum were studied. Additionally, different A. paragallinarum vaccines were made using the same nanomaterials at a concentration of 400 µg/ml to help control infectious coryza disease in chicken. A concentration of 400 µg/ml of all the NPs tested was the best concentration for the inactivation of A. paragallinarum. Additionally, this study showed that the infectious coryza vaccine adjuvanted with SiO 2 NPs had the highest immune response, followed by the infectious coryza vaccine adjuvanted with Fe 3 O 4 NPs, the infectious coryza vaccine adjuvanted with SiO 2 -CS NPs, and the infectious coryza vaccine adjuvanted with O.CS NPs in comparison with the infectious coryza vaccine adjuvanted with liquid paraffin (a commercial vaccine)., (© 2024. The Author(s).)

Controlling avian influenza viruses (AIVs) is mainly based on culling of the infected bird flocks or via the implementation of inactivated vaccines in countries where AIVs are considered to be endemic. Over the last decade, several avian influenza virus subtypes, including highly pathogenic avian influenza (HPAI) H5N1 clade 2.2.1.2, H5N8 clade 2.3.4.4b and the recent H5N1 clade 2.3.4.4b, have been reported among poultry populations in Egypt. This demanded the utilization of a nationwide routine vaccination program in the poultry sector. Antigenic differences between available avian influenza vaccines and the currently circulating H5Nx strains were reported, calling for an updated vaccine for homogenous strains. In this study, three H5Nx vaccines were generated by utilizing the reverse genetic system: rgH5N1_2.3.4.4, rgH5N8_2.3.4.4 and rgH5N1_2.2.1.2. Further, the immunogenicity and the cross-reactivity of the generated inactivated vaccines were assessed in the chicken model against a panel of homologous and heterologous H5Nx HPAIVs. Interestingly, the rgH5N1_2.3.4.4 induced high immunogenicity in specific-pathogen-free (SPF) chicken and could efficiently protect immunized chickens against challenge infection with HPAIV H5N1_2.3.4.4, H5N8_2.3.4.4 and H5N1_2.2.1.2. In parallel, the rgH5N1_2.2.1.2 could partially protect SPF chickens against infection with HPAIV H5N1_2.3.4.4 and H5N8_2.3.4.4. Conversely, the raised antibodies to rgH5N1_2.3.4.4 could provide full protection against HPAIV H5N1_2.3.4.4 and HPAIV H5N8_2.3.4.4, and partial protection (60%) against HPAIV H5N1_2.2.1.2. Compared to rgH5N8_2.3.4.4 and rgH5N1_2.2.1.2 vaccines, chickens vaccinated with rgH5N1_2.3.4.4 showed lower viral shedding following challenge infection with the predefined HPAIVs. These data emphasize the superior immunogenicity and cross-protective efficacy of the rgH5N1_2.3.4.4 in comparison to rgH5N8_2.3.4.4 and rgH5N1_2.2.1.2.

Exercise, capture, and handling stress in fish can elevate extracellular K + concentration ([K + ] o ) with potential impact on heart function in a temperature- and frequency-dependent manner. To this end, the effects of [K + ] o on the excitability of ventricular myocytes of winter-acclimatized roach ( Rutilus rutilus) (4 ± 0.5°C) were examined at different test temperatures and varying pacing rates. Frequencies corresponding to in vivo heart rates at 4°C (0.37 Hz), 14°C (1.16 Hz), and 24°C (1.96 Hz) had no significant effect on the excitability of ventricular myocytes. Acute increase of temperature from 4 to 14°C did not affect excitability, but a further rise to 24 markedly decreased excitability: stimulus current and critical depolarization needed to elicit an action potential (AP) were ~25 and 14% higher, respectively, at 24°C than at 4°C and 14°C ( P < 0.05). This depression could be due to temperature-related mismatch between inward Na + and outward K + currents. In contrast, an increase of [K + ] o from 3 to 5.4 or 8 mM at 24°C reduced the stimulus current needed to trigger AP. However, other aspects of excitability were strongly depressed by high [K + ] o : maximum rate of AP upstroke and AP duration were drastically (89 and 50%, respectively) reduced at 8 mM [K + ] o in comparison with 3 mM ( P < 0.05). As an extreme case, some myocytes completely failed to elicit all-or-none AP at 8 mM [K + ] o at 24°C. Also, amplitude and overshoot of AP were reduced by elevation of [K + ] o ( P < 0.05). Although high [K + ] o antagonizes the negative effects of high temperature on excitation threshold, the precipitous depression of the rate of AP upstroke and complete loss of excitability in some myocytes suggest that the combination of high temperature and high [K + ] o will severely impair ventricular excitability in roach.

To test the hypothesis of temperature-dependent deterioration of electrical excitability (TDEE) (Vornanen, J Exp Biol 219:1941-1952, 2016), the role of sodium (I Na ) and calcium (I Ca ) currents in heat tolerance of cardiac excitability was examined in a eurythermic fish, the roach (Rutilus rutilus). Densities of cardiac I Ca and I Na and their acute heat tolerance were measured in winter-acclimatized (WiR) and summer-acclimatized (SuR) fish maintained in the laboratory at 4 ± 1 and 18 ± 1 °C, respectively. A robust L-type Ca 2+ current (I CaL ), but no T-type Ca 2+ current, was present in roach atrial and ventricular myocytes. Peak density of I CaL was smaller in atrial (- 1.97 ± 0.14 and - 1.75 ± 0.19 pA/pF for WiR and SuR, respectively) than ventricular myocytes (- 4.00 ± 0.59 and - 2.88 ± 0.47 pA/pF for WiR and SuR, respectively) (p < 0.05), but current density and heat tolerance of I CaL did not change between seasons in either cell type. In contrast to I Ca , marked differences appeared in I Na between WiR and SuR. I Na density was 38% higher in WiR than SuR atrial myocytes (- 80.03 ± 5.92 vs. - 49.77 ± 4.72 pA/pF; p < 0.05) and 48% higher in WiR than SuR ventricular myocytes (- 39.25 ± 3.06 vs. - 20.03 ± 1.79 pA/pF; p < 0.05). The winter increase in I Na density was associated with 55% (1.70 ± 0.27 vs. 0.77 ± 0.12) and 54% (1.08 ± 0.19 vs. 0.50 ± 0.10) up-regulation of the total Na + channel (scn4 + scn5 + scn8) transcripts in atrium and ventricle, respectively (p < 0.05). Heat tolerance of atrial I Na was lower in WiR with a breakpoint temperature of 20.3 ± 1.2 °C than in SuR (23.8 ± 0.7 °C) (p < 0.05). The response of I Na to seasonal acclimatization conforms to the TDEE hypothesis. The lower heat tolerance of I Na in WiR is consistent with the lower heat tolerance of in vivo heart rate in WiR in comparison to SuR, but the match is not quantitatively perfect, suggesting that other factors in addition to I Na may be involved.

Temperature sensitivity of electrical excitability is a potential limiting factor for high temperature tolerance of ectotherms. The present study examines whether heat resistance of electrical excitability of cardiac myocytes is modified by seasonal thermal acclimatization in roach (Rutilus rutilus), a eurythermal teleost species. To this end, temperature dependencies of ventricular action potentials (APs), and atrial and ventricular K + currents were measured from winter-acclimatized (WiR) and summer-acclimatized (SuR) roach. Under patch-clamp recording conditions, ventricular APs could be triggered over a wide range of temperatures (4-43°C) with prominent changes in resting membrane potential (RMP), AP duration and amplitude. In general, APs of SuR were slightly more tolerant to high temperatures than those of WiR, e.g. the break point temperature (T BP ) of RMP was 37.6±0.4°C in WiR and 41±1°C in SuR (p<0.05). Of the two major cardiac K + currents, the inward rectifier K + current (I K1 ) was particularly heat resistant in both SuR (T BP 39.4±0.4°C) and WiR (T BP 40.0±0.4°C) ventricular myocytes. The delayed rectifier K + current (I Kr ) was not as heat resistant as I K1 . Surprisingly, I Kr of WiR tolerated heat better (T BP 31.9±0.8°C) than I Kr of SuR (T BP 24.1±0.5°C) (p<0.05). I Kr (Erg2) channel transcripts of both atrial and ventricular myocytes were up-regulated in WiR. I K1 (Kir2) channel transcripts were not affected by seasonal acclimatization, although ventricular I K1 current was up-regulated in summer. Collectively, these findings show that thermal tolerance limits of K + currents in isolated myocytes between seasonally acclimatized roach are much less pronounced than the heat sensitivity of ECG variables in intact fish., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: Approximately 13% of Canadian mothers report difficulty accessing health care for their infants, yet little is known about the factors associated with difficulty. Therefore, we examined factors associated with difficulty accessing non-routine health care for Canadian infants, from birth to 14 months of age, as reported by their mothers., Methods: Data was drawn from the Maternity Experiences Survey (MES), a cross-sectional, nationally representative survey of mothers who gave birth between November 2005 and May 2006, aged 15 years or older, and lived with their infants at the time of survey administration. A multivariable logistic regression analysis was conducted to determine factors associated with reporting difficulty, with difficulty defined as a mother reporting it being somewhat or very difficult to access a health care provider., Results: Analysis of 2832 mothers who reported needing to access a health care provider for their infant for a non-routine visit found that 13% reported difficulty accessing a provider. Factors associated with reporting difficulty were: residing in Quebec (aOR 1.89, 95% CI: 1.31-2.73), being an immigrant (aOR 1.58, 95% CI: 1.10-2.27), mistimed pregnancy (aOR 1.44, 95% CI: 1.05-1.98), low level of social support (aOR 1.69, 95% CI: 1.05-2.73), good health (aOR 1.88, 95% CI: 1.43-2.47), postpartum depression symptoms (aOR 1.55, 95% CI: 1.02-2.37) and a self-reported 'too-short' postpartum hospital stay (aOR 1.69, 95% CI: 1.21-2.35). Additionally, accessing care for an infant with a birth weight of 2500 g or more (aOR 2.43, 95% CI: 1.02-5.82), was associated with reporting difficulty. Household income, mothers' level of education, marital status, Aboriginal ethnicity, and size of community of residence were not associated with difficulty accessing care., Conclusions: Ease of health care access for Canadian infants is not equal, suggesting that efforts to improve access should be tailored to groups facing increased difficulties.

Temperature sensitivity of electrical excitability is a potential limiting factor for performance level and thermal tolerance of excitable tissues in ectothermic animals. To test whether the rate and rhythm of the heart acclimatize to seasonal temperature changes, thermal sensitivity of cardiac excitation in a eurythermal teleost, the roach (Rutilus rutilus), was examined. Excitability of the heart was determined from in vivo electrocardiograms and in vitro microelectrode recordings of action potentials (APs) from winter and summer roach acclimatized to 4 and 18°C, respectively. Under heat ramps (3°C h(-1)), starting from the acclimatization temperatures of the fish, heart rate increased to maximum values of 78±5 beats min(-1) (at 19.8±0.5°C) and 150±7 beats min(-1) (at 28.1±0.5°C) for winter and summer roach, respectively, and then declined in both groups. Below 20°C, heart rate was significantly higher in winter than in summer roach (P<0.05), indicating positive thermal compensation. Cardiac arrhythmias appeared with rising temperature as missing QRS complexes, increase in variability of heart rate, episodes of atrial tachycardia, ventricular bradycardia and complete cessation of the heartbeat (asystole) in both winter and summer roach. Unlike winter roach, atrial APs of summer roach had a distinct early repolarization phase, which appeared as shorter durations of atrial AP at 10% and 20% repolarization levels in comparison to winter roach (P<0.05). In contrast, seasonal acclimatization had only subtle effects on ventricular AP characteristics. Plasticity of cardiac excitation appears to be necessary for seasonal improvements in performance level and thermal resilience of the roach heart., (© 2016. Published by The Company of Biologists Ltd.)

This paper presents a novel approach for search engine results clustering that relies on the semantics of the retrieved documents rather than the terms in those documents. The proposed approach takes into consideration both lexical and semantics similarities among documents and applies activation spreading technique in order to generate semantically meaningful clusters. This approach allows documents that are semantically similar to be clustered together rather than clustering documents based on similar terms. A prototype is implemented and several experiments are conducted to test the prospered solution. The result of the experiment confirmed that the proposed solution achieves remarkable results in terms of precision.

Background: Physician trainees in neonatology can find it extremely challenging to care for patients from diverse linguistic and multicultural backgrounds. This challenge is particularly highlighted when difficult and ethically challenging end-of-life (EOL) decision-making with parents is required. While these interactions are an opportunity for growth and learning, they also have the potential to lead to misunderstanding and uncertainty and can add to trainees' insecurity, unpreparedness and stress when participating in such interactions., Objectives: To explore the challenges for trainees when EOL decisions are undertaken and to encourage them to reflect on how they might influence such decision-making., Design and Interview: An in-depth, semi-structured interview guide was developed: the interview questions address trainees' beliefs, attitudes, preferences and expectations regarding discussions of EOL neonatal care. Twelve interviews were completed and the audio records transcribed verbatim, after removal of identifying personal information., Results: Participants identified six domains of challenge in EOL care: withdrawal of life-sustaining treatment based on poor outcome, explaining 'no resuscitation options' to parents, clarifying 'do not resuscitate (DNR)' orders, empowering families with knowledge and shared decision-making, dealing with different cultures and managing personal internal conflict. Participants experienced the most difficulty during the initial stages of training and eventually reported good knowledge of the EOL care process. They had a sense of security and confidence working within a multidisciplinary care team, which includes experienced nursing staff as well as bereavement and palliative care coordinator within the neonatal intensive care unit., Conclusions: The challenges experienced by physician trainees when providing EOL care can serve as focal points for improving EOL educational programmes for neonatal fellowship training.

Background: Cytomegalovirus is the most common pathogen causing congenital infection and can result in significant neurodevelopmental adverse outcomes. For this reason, it is the standard of care in many regions to treat congenital cytomegalovirus infection involving the brain with six weeks of ganciclovir. There have been no reports in the published literature of significant cytomegalovirus neonatal infection in infants previously treated for congenital infection., Case Presentation: A preterm male infant with congenital symptomatic cytomegalovirus infection was initially treated with over 8 weeks of ganciclovir between the ages of 3 and 14 weeks. At four months chronologic age, just prior to planned discharge, he developed an episode of life-threatening multisystem cytomegalovirus disease notable for severe pneumonitis, encephalitis, hepatitis, and disseminated intravascular coagulation. This disease resolved after re-treatment with a prolonged course of intravenous ganciclovir and oral valganciclovir., Conclusions: Clinicians should be aware of the possibility of recurrence of congenital cytomegalovirus infection, especially in preterm infants. Serial plasma cytomegalovirus viral load monitoring may have a role in the management of premature infants treated with ganciclovir; had the diagnosis of recrudescent cytomegalovirus infection been considered sooner, specific therapy might have been more quickly initiated and perhaps further morbidity would have been prevented.

Background: The judicious prescription of antibiotics has become a central focus of professional and public health measures to combat the spread of resistant organisms., Materials and Methods: A one-year multi-center prospective follow-up study of 1,320 healthy infants was conducted. The study aim was to determine the prevalence and identify the predictors of antibiotics misuse in viral respiratory illnesses among healthy infants in the first year of life. Infants born between August 2001 and February 2002 were recruited through the clinics and dispensaries of 117 pediatricians located in the Greater Beirut area of Lebanon. On each routine visit from birth until one year of life, pediatricians reported any episodes of upper respiratory tract infection (URTI; common cold) and bronchiolitis, as well as the treatment type, duration, and dose. Predictors that were considered included infant, maternal, and pediatrician characteristics., Results: Of the 1,320 recruited infants, 770 (58.3%) had common cold or acute bronchiolitis on at least one occasion during the study period. Pediatricians prescribed antibiotics at least once in 21.4% of cases diagnosed as the common cold and 45.5% of cases of acute bronchiolitis. Logistic regression analysis revealed that antibiotics misuse was more common among infants born to mothers with lower educational levels (odds ratio [OR] = 1.6; 95% confidence interval [CI]: 1.1-2.3). Furthermore, pediatricians tend to prescribe antibiotics in dispensaries more often than in private clinics (OR = 1.4; 95% CI: 1.0-2.3)., Conclusion: This study shows a substantial quantity of antibiotics prescriptions for common cold and acute bronchiolitis in our population. Our findings suggest that lower maternal education and pediatricians working in dispensaries (versus private clinics) are associated with increased antibiotics misuse.

Autoimmunity to brain could play an etiopathogenic role in a subgroup of autistic patients. The frequency of serum anti-myelin-associated glycoprotein antibodies, as an index for autoimmunity to brain, and their relation to family history of autoimmunity were investigated in 32 autistic and 32 healthy matched children. Autistic children had significantly higher serum anti-myelin-associated glycoprotein antibodies than healthy children (2100 [1995] and 1138 [87.5] Buhlmann titre unit, P < .001). Anti-myelin-associated glycoprotein positivity was elicited in 62.5% of autistic children. Family history of autoimmunity in autistic children (50%) was significantly higher than controls (9.4%). Anti-myelin-associated glycoprotein serum levels were significantly higher in autistic children with than those without such history (P < .05). In conclusion, autism could be, in part, one of the pediatric autoimmune neuropsychiatric disorders. Further studies are warranted to shed light on the etiopathogenic role of anti-myelin-associated glycoprotein antibodies and the role of immunotherapy in autism.

Objective: To determine the effect of morphine on duration of mechanical ventilation, apnoea and hypotension among full-term neonates who underwent thoracic or abdominal surgery in a level III neonatal intensive care unit., Method: Medical records of 82 infants were reviewed retrospectively and data including patient demographics, clinical diagnosis, type of surgery, postoperative opioid administration, duration of mechanical ventilation, hypotension, apnoea and pain scores (premature infant pain profile (PIPP) score) were collected., Result: Sixty-two neonates (76%) received morphine following surgery as a continuous intravenous infusion during the postoperative period. Linear regression analysis showed that morphine dosage and duration were significantly associated with the duration of mechanical ventilation. An increase in morphine infusion rate by 10 microg kg(-1) h(-1) was associated with an increase in the duration of mechanical ventilation by 24 h (P<0.0001) and an increase in morphine duration of 1 hour was associated with a longer duration of mechanical ventilation by 38 min (P<0.0001). Logistic regression analysis showed no association between morphine infusion rate or duration and hypotension. Apnoea was not associated with morphine dosage or duration of infusion in neonates receiving morphine following extubation. Score on the PIPP correlated significantly with morphine infusion rate across time (r=0.47, P<0.01)., Conclusion: Postoperative morphine dose and duration may prolong the duration of mechanical ventilation but there are no significant dose-dependent effects on other parameters including apnoea or hypotension following extubation in term neonates. More research is needed to determine the safety profile of morphine for management of pain in non-ventilated neonates.

A linear electrohydrodynamic instability analysis is presented for an inviscid dielectric liquid sheet emanated into an inviscid dielectric gas medium in the presence of a horizontal electric field. The influence of Weber number, gas-to-liquid density ratio, and the applied electric field on the evolution of two-, and three-dimensional disturbances of symmetrical and antisymmetrical types is studied. It is found, for antisymmetrical waves, that two-dimensional disturbances always prevail over three-dimensional disturbances, regardless of Weber number or gas-to-liquid density ratio values, especially for long waves; while for short waves, both two- and three-dimensional disturbances grow at approximately the same rate. It is also found, for symmetrical waves, that two-dimensional disturbances always dominate the instability process at low Weber number, and when the Weber number is large, symmetrical three-dimensional disturbances become more unstable than two-dimensional ones for long waves. The effect of increasing the gas-to-liquid density ratio is to promote the dominance of long three-dimensional symmetrical waves over their two-dimensional counterpart. Finally, the equilibrium Weber number at which the growth rates of two- and three-dimensional modes are equal is discussed for both symmetrical- and antisymmetrical-disturbances cases.

Successful renal transplantation corrects many of the metabolic abnormalities associated with the development of renal osteodystrophy, but despite a well-functioning graft osteopenia, growth failure, spontaneous fractures, and avascular necrosis remain prevalent in adult and pediatric kidney recipients. A paucity of information exists regarding the effects of different therapies to prevent and treat bone loss in the renal transplant recipients. We constructed a design to study the effect of different modalities of treatment on bone mass in our renal transplant children. Among 93 patients who underwent renal transplantation at the age of 17 yr or less and were subjected to dual-energy X-ray absorptiometry (DEXA), we blindly randomized 60 patients who had osteopenia or osteoporosis (T-score = -1 by DEXA) in a prospective study. Their mean age at time of transplantation was 13.4 +/- 4.3 yr. The mean duration after transplantation was 48 +/- 34 months. The patients were classified randomly into four groups. Each group consisted of 15 patients: group 1 was the control group, group 2 received oral alfacalcidol 0.25 microg daily, group 3 received oral alendronate 5 mg daily, and group 4 received 200 IU/day nasal spray calcitonin. Parameters of bone turnover, calcium metabolism, and DEXA were measured before and after 12 months of treatment duration. The characteristics of all groups were comparable at the beginning of the study. At the lumber spine, bone mass density decreased from -2.4 to -2.8 in group 1, increased from -2.3 to -0.5 in group 2, from -2.3 to -1.9 in group 3, and from -2.3 to -1.0 in group 4. The four groups had similar patient profiles, serum creatinine, intact parathyroid hormone, osteocalcin, and deoxypyridinoline. This study confirmed the value of alfacalcidol and antiresorptive agents in the treatment of osteopenia and osteoporosis in young renal transplant recipients.These therapies were safe, tolerable, simple to administer and potentially applicable to other renal transplant patients., (Copyright 2004 Blackwell Munksgaard)

Peptide fractions were isolated from venoms of the Egyptian snake Naja haje haje (cobra BPP) and the scorpions Buthus occitanus (BPP(B)) and Leirus quenquestriatus (BPP(L)). The pharmacological effects of these peptides were bioassayed and showed bradykinin potentiating activities. Amino acid analysis revealed that 14 amino acids contribute to the structure of BPP(B) and 16 for BPP(L), while cobra BPP was composed of 15 amino acids. Treatment of rat atrial preparations with 50 microg/ml of cobra BPP caused a significant reduction (P<0.001) in myocardial force. Elevation of extracellular calcium concentration from 1.25 to 5 mM antagonized the effect of cobra BPP in a way that restored the atrial force development. Na(+)-channel blockers did not change the force development at 5 mM Ca(2+). Experiments with (45)Ca revealed that Ca(2+) uptake of cobra BPP treated atria was 0.52+/-0.07 microM/g wet mass and the force at the end of the uptake period was 55.0+/-2.0%. The corresponding values for non-treated preparations were 0.56+/-0.04 microM/g and 92.0%+/-3.0%, respectively. Our results revealed that cobra BPP did not exhibit any effect on Ca(2+) uptake by rat atrial preparations, but strongly affected cellular Ca(2+) regulation.

The instability of a thin sheet of dielectric liquid moving in the same direction as an air stream in the presence of a uniform horizontal electric field is studied theoretically. It is found that aerodynamic-enhanced instability occurs if the Weber number is much less than a critical value related to the ratio of the air and liquid stream velocities, the electric field, and the dielectric constant values. The electric field is found to have a stabilizing effect, and there exists a critical Weber number above which instability is suppressed by the surface tension effect. The condition for disintegrating the sheet is obtained in terms of the electric field values, and some limiting cases are recovered.

The role played by the sarcoplasmic reticulum in force development and in cellular Ca2+ balance and its dependence on extracellular K+ were examined in heart ventricular tissue of rainbow trout and plaice. Compared with the steady-state twitch at a stimulation rate of 0.2 Hz, a 30-s rest led to a similar increase in twitch force in trout heart, regardless of whether [K+] was 2.5 or 5 mM. At 5 mM (but not at 2.5 mM) post-rest potentiation increased with increasing rest periods (from 30 to 900 s). These post-rest potentiations were removed or transformed into a loss of force by 10 microM ryanodine or 8 mM caffeine. In the plaice heart, where the sarcoplasmic reticulum is claimed to be sparse, the post-rest potentiation and the influence of ryanodine were small. The Ca2+ uptake measured during 5 min with 45Ca in the trout heart was higher in 5 than in 2.5 mM K+, regardless of the concomitant stimulation rate. This effect of K+ was removed by 10 microM ryanodine. The twitch force after 5 min of rest correlated significantly with the Ca2+ uptake, whereas the twitch force developed at a rate of 0.2 or 1.0 Hz did not. In conclusion, an elevation of K+ appears to stimulate the Ca2+ uptake of the sarcoplasmic reticulum. The twitch force after prolonged rest seems to relate to the Ca2+ contained in this organelle, whereas this does not apply to the twitch force developed at more physiological rates (0.2 or 1 Hz).