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Ca(2+) signaling, particularly the mechanism via store-operated Ca(2+) entry (SOCE) and receptor-operated Ca(2+) entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca(2+)] ([Ca(2+)](cyt)) and the stored [Ca(2+)] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca(2+) oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na(+)/Ca(2+) exchanger-mediated increases in [Ca(2+)](cyt) did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O(2) for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca(2+)](cyt) only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca(2+) channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

Ghrelin and its synthetic analogue hexarelin are specific ligands of GH secretagogue receptor (GHS-R) and induce a variety of cardiovascular protective and cardiac positive inotropic effects. The signaling system underlying immediate effects of both GHSs in cardiomyocytes remains undefined. In the present study, we investigated the immediate effects of GHSs on isolated ventricular myocyte shortening, intracellular Ca(2+) ([Ca(2+)](i)) transients, and the L-type Ca(2+) current (I(Ca,L)). Putative intracellular signalling cascades were studied with specific receptor and signalling blockers. In fresh isolated adult Wistar rat ventricular myocytes, GHSs produced a positive inotropic effect in a concentration-dependent manner and increased the amplitude of [Ca(2+)](i) transients and the I(Ca,L). The positive inotropic response was abolished by the GHS-R1a antagonist [D-Lys(3)]-GH-releasing peptide-6 (10 microm). GHS-induced increase in the I(Ca,L) was abolished by [D-Lys(3)]-GH-releasing peptide-6 and protein kinase C inhibitor, chelerythrine chloride (5 microm), but not by protein kinase A inhibitor, KT 5720 (10 microm). We conclude that hexarelin and ghrelin increase the I(Ca,L), through GHS-R1a receptor and protein kinase C signalling cascade, which contribute to its direct positive inotropic effect on cardiomyocytes.

Intracellular free Ca2+ (Ca(i)2+) is an important regulator of many cellular activities; however, Ca2+ signaling is not well studied in human preadipocytes. The purpose of the present study was to characterize Ca2+ signal pathways using a confocal scanning technique and RT-PCR. It was found that spontaneous Ca(i)2+ oscillations were observed in 12.1% preadipocytes, and number of cells with Ca2+ oscillations was increased to 47.9% by 1% fetal bovine serum. Ca(i)2+ oscillations were dependent on Ca2+ entry mainly via stored-operated Ca2+ (SOC) entry. They were suppressed by the SOC entry channel blocker La3+, the phospholipase C (PLC) inhibitor U73122, the inositol trisphosphate receptor (IP3R) blocker 2-amino-ethoxydiphenyl borate, or the sarcoplasmic/endoplasmic reticulum Ca2+ pump (SERCA) inhibitors thapsigargin and cyclopiazonic acid, but not by ryanodine. The IP3R activator thimerosal increased Ca(i)2+ oscillations. In addition, the plasma membrane Ca2+ pump (PMCA) inhibitor carboxyeosin and Na+--Ca2+ exchanger (NCX) inhibitor Ni2+ both suppressed Ca2+ oscillations. RT-PCR revealed that the mRNAs for IP3R1-3, SERCA1,2, NCX3 and PMCA1,3,4, Ca(V)1.2, and TRPC1,4,6, STIM1 and Orai1 (for SOC entry channels) were significant in human preadipocytes. The present study demonstrates that multiple Ca2+ signal pathways are present in human preadipocytes, and provides a basis for investigating how Ca2+ signals regulate biological and physiological activities of human preadipocytes.

The present study was designed to investigate the relaxant effect of isopropyl 3-(3, 4-dihydroxyphenyl)-2-hydroxypropanoate (IDHP), a new metabolite from Salvia miltiorrhiza, on rat mesenteric artery. Isolated mesenteric arterial rings were mounted in organ baths and the isometric tension changes were measured continuously by a sensitive myograph system. The results showed that IDHP at concentrations greater than 0.1 nM produced a concentration-dependent relaxation of artery contracted by norepinephrine with pEC(50) of 7.41+/-0.08. Removal of the endothelium did not affect this relaxation, suggesting that IDHP exerted a direct effect on vascular smooth muscle cells. Meanwhile, the vasorelaxant effect of IDHP was unaffected by pre-treatment with ATP-sensitive K(+) channel inhibitor glibenclamide, delayed rectifier K(+) channel inhibitor 4-aminopyridine, inwardly rectifying K(+) channel inhibitor barium chloride and beta-adrenoceptor antagonist propranolol. However, the non-specific K(+) channel inhibitor tetraethylammonium (TEA, 3 mM) produced a rightward shift of 1.8 fold on the concentration-response curve of IDHP. Moreover, IDHP shifted the concentration-response curve of CaCl(2) as well as two receptor-mediated constrictors, phenylephrine and 5-hydroxytryptamine, to the right in a non-parallel manner. In the absence of extracellular Ca(2+), IDHP depressed the contractions induced by norepinephrine and CaCl(2), and the maximal inhibitions were 48.3+/-18.9% and 58.4+/-10.9%, respectively. These results suggest that IDHP exerts a vasorelaxant effect by inhibiting both Ca(2+) release from intracellular stores and Ca(2+) influx through voltage-dependent calcium channels, and receptor-operated calcium channels in vascular smooth muscle cells. In addition, activation of vascular TEA-sensitive K(+) channels may be partially involved in the relaxant effect of IDHP.

Heart and blood vessels are the pivotal organs that make up of the important system, cardiovascular system, of the body. They are associated functionally and both have the contractility. The pressure of the ventricles can elevate to a high level in a short time when heart contracts, so the cardiomyocytes should contract rapidly and powerfully. The contractile structure and the process of the calcium-modulation are required to meet the demand. The contractility of blood vessels is of slow and per durable characters which are compatible to the related function. This article describes the contractive structure and mechanism, and the related calcium-modulation mechanism cytologically, furthermore, introduces their differences and similarities, respectively.

The purpose of this study was to investigate the different effects of ACh on the action potential and force contraction in guinea pig atrial and ventricular myocardium by using standard microelectrodes and force transducer. The results showed that the duration of the action potential (APD) of atrial myocardium was shortened from 208.57+/-36.05 to 101.78+/-14.41 ms (n=6, P0.01), and the APD of the ventricular myocardium was shortened from 286.73+/-36.11 to 265.16+/-30.06 ms (n=6, P0.01).The amplitude of the action potential (APA) of the atrial myocardium was decreased from 88.00+/-9.35 to 62.62+/-20.50 mV (n=6, P0.01), while the APA of the ventricular myocardium did not change significantly.The force contraction of atrial myocardium was inhibited completely (n=6, P0.01), while the force contraction of ventricular myocardium was inhibited by 37.57+/-2.58% (n=6, P0.01). The ACh effects correlated with its concentration. The K(D) of the APD shortening effects in the atrial and ventricular myocardium were 0.275 and 0.575 micromol/L. The K(D) of the negative inotropic in the atrial and ventricular myocardium were 0.135 and 0.676 micromol/L, respectively. The corresponding data points were compared using t test between the atrial and ventricular myocardium, and the differences were significant when the ACh concentration was above 10 nmol/L. Furthermore, atropine (10 micromol/L) and CsCl (20 mmol/L) blocked the effects of 10 micromol/L ACh on the APD of ventricular myocardium, while CdCl2 (0.1 mmol/L) had no influence on these effects. In conclusion, ACh could shorten the action potential duration and inhibit the force contraction of atrial and ventricular myocardium in a concentration-dependent manner. There are differences in the effects of ACh on the atrial and ventricular myocardium. The atrial myocardium is more sensitive to ACh than the ventricular myocardium. It is probable that the muscarinic receptor and the potassium channel, but not the calcium channel, are involved in the ACh-induced shortening of the ventricular APD.

The whole-cell patch clamp technique was used to investigate the effect of different charge carriers upon ultra-slow voltage-dependent inactivation of L-type Ca2+ channel current in ferret ventricular myocytes at 37 degrees C. Intracellular Ca2+ was buffered with 10 mM EGTA and the membrane potential held at -40 mV. With Ba2+ as the charge carrier, the L-type current decayed throughout 20 s pulses to 0 mV as a result of ultra-slow voltage-dependent inactivation. In contrast, with Ca2+ as the charge carrier, there was no such slow decay of the current as the current decayed almost completely in the first approximately 100 ms as a result of Ca(2+)-dependent inactivation. However, with Ca2+ as the charge carrier it is still possible that ultra-slow voltage-dependent inactivation occurs. A conditioning-test pulse protocol and a second protocol were used to test for the development of ultra-slow inactivation during 20 or 30 s pulses to 0 mV with Ca2+ as the charge carrier. Ultra-slow inactivation did occur and it was qualitatively similar to that with Ba2+ as the charge carrier. The onset of ultra-slow inactivation with Ca2+ as the charge carrier could be described by the sum of two exponentials with time constants of 0.3 and 6.7 s. Recovery from ultra-slow inactivation with Ca2+ as the charge carrier was also measured with a conditioning-test pulse protocol and was best described by the sum of two exponentials with time constants of 0.5 and 6.2 s. We conclude that ultra-slow inactivation of the L-type current does occur with the physiological charge carrier, Ca2+, but it is normally masked by Ca(2+)-dependent inactivation.

L-type Ca2+ current, iCa, has been recorded in guinea-pig ventricular myocytes at 36 degrees C using the whole cell patch clamp technique. Intracellular Ca2+ was buffered with ethylenebis(oxonitrilo)tetraacetate (EGTA). An increase in the rate of stimulation from 0.5 to 3 Hz resulted in an abrupt decrease in iCa in the first beat at the high rate, followed by a progressive decrease (tau approx. 7 s) over the next 30 s. The changes were not the result of Ca(2+)-dependent inactivation, because similar changes occurred with either Ba2+ or Na+ as the charge carrier. During 20-s voltage clamp pulses there was an ultra-slow phase of inactivation of Ba2+ or Na+ current through the Ca2+ channel (tau approx. 6 s at 0 mV). This was confirmed by applying test pulses after conditioning pulses of different duration: the Ba2+ current during the test pulse decreased progressively when the duration of the conditioning pulse was increased progressively to 20 s. Ultra-slow inactivation of Ba2+ current was voltage dependent and increased monotonically at more positive potentials. Recovery of Ba2+ current from ultra-slow inactivation occurred with a time constant of 3.7 s at -40 mV and 0.7 s at -80 mV. The gradual decrease in iCa on increasing the rate to 3 Hz may have been the result of the development of ultra-slow voltage-dependent inactivation.