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Autonomic regulation plays a central role in cardiac contractility and excitability in numerous vertebrate species. However, the role of autonomic regulation is less understood in fish physiology. Here, we used Goldfish as a model to explore the role of autonomic regulation. A transmural electrocardiogram recording showed perfusion of the Goldfish heart with isoproterenol increased the spontaneous heart rate, while perfusion with carbamylcholine decreased the spontaneous heart rate. Cardiac action potentials obtained via sharp microelectrodes exhibited the same modifications of the spontaneous heart rate in response to isoproterenol and carbamylcholine. Interestingly, the duration of the cardiac action potentials lengthened in the presence of both isoproterenol and carbamylcholine. To evaluate cardiac contractility, the Goldfish heart was perfused with the Ca2+ indicator Rhod-2 and ventricular epicardial Ca2+ transients were measured using Pulsed Local Field Fluorescence Microscopy. Following isoproterenol perfusion, the amplitude of the Ca2+ transient significantly increased, the half duration of the Ca2+ transient shortened, and there was an observable increase in the velocity of the rise time and fall time of the Ca2+ transient, all of which are compatible with the shortening of the action potential induced by isoproterenol perfusion. On the other hand, carbamylcholine perfusion significantly reduced the amplitude of the Ca2+ transient and increased the half duration of the Ca2+ transient. These results are interesting because the effect of carbamylcholine is opposite to what happens in classically used models, such as mouse hearts, and the autonomic regulation of the Goldfish heart is strikingly similar to what has been observed in larger mammalian models resembling humans. [ABSTRACT FROM AUTHOR]

Autonomic regulation plays a central role in cardiac contractility and excitability in numerous vertebrate species. However, the role of autonomic regulation is less understood in fish physiology. Here, we used Goldfish as a model to explore the role of autonomic regulation. A transmural electrocardiogram recording showed perfusion of the Goldfish heart with isoproterenol increased the spontaneous heart rate, while perfusion with carbamylcholine decreased the spontaneous heart rate. Cardiac action potentials obtained via sharp microelectrodes exhibited the same modifications of the spontaneous heart rate in response to isoproterenol and carbamylcholine. Interestingly, the duration of the cardiac action potentials lengthened in the presence of both isoproterenol and carbamylcholine. To evaluate cardiac contractility, the Goldfish heart was perfused with the Ca2+ indicator Rhod-2 and ventricular epicardial Ca2+ transients were measured using Pulsed Local Field Fluorescence Microscopy. Following isoproterenol perfusion, the amplitude of the Ca2+ transient significantly increased, the half duration of the Ca2+ transient shortened, and there was an observable increase in the velocity of the rise time and fall time of the Ca2+ transient, all of which are compatible with the shortening of the action potential induced by isoproterenol perfusion. On the other hand, carbamylcholine perfusion significantly reduced the amplitude of the Ca2+ transient and increased the half duration of the Ca2+ transient. These results are interesting because the effect of carbamylcholine is opposite to what happens in classically used models, such as mouse hearts, and the autonomic regulation of the Goldfish heart is strikingly similar to what has been observed in larger mammalian models resembling humans.

Abstract: On May 10th 2010 Platon Grigorevitch Kostyuk sadly left us at the age of 85. He was a talented scientist, a brilliant experimenter, an outstanding organizer of science and an excellent teacher. Platon Kostyuk was born in 1924 in Kiev, Ukraine. He obtained a double education: a graduate of the Kiev University Department of Biology in 1946 and the Kiev Medical Institute in 1949, he became a pioneer in neuroscience, the first in the Soviet Union to use microelectrodes for intracellular recording of electrical signals in neurons. Despite the difficulties for international travel for those living behind the Iron Curtain, he was able to present his work at the International Congress of Physiology in Buenos Aires in 1959 and here met Prof. John Eccles who invited him to work at the University of Canberra in Australia in 1960–1961. This was the start of an outstanding international career, complementing his creative achievements in the Soviet Union. In 1966 P.G. Kostyuk became director of the Bogomoletz Institute of Physiology in Kiev, which he headed for nearly 45years. Under his direction this Institute became a leading centre for neuroscience, renowned not only in the Soviet Union but also internationally. New directions of research were developed in cell physiology, molecular biophysics and neurophysiology. Several important discoveries were made including the development of a method for intracellular perfusion, evidence for a calcium-dependent conductance in nerve cells and the discovery of new types of ion channels. Elected to the Ukraine Academy of Science in 1969 and Grand Academician of the Soviet Academy of Science in 1974, Kostyuk has also been honoured by many international societies. He is the author of more than 650 articles, 17 monographs and 7 discoveries and was the creator and editor of two scientific journals: “Neurophysiology” and “Neuroscience”. The outstanding career and multifaceted activities of Academician Platon Kostyuk form a pyramid of achievement, at the top of which ride his research in cognition and his enthusiasm for the discovery of the secrets of Nature. [Copyright &y& Elsevier]

Microelectrodes and electron microprobe analysis were employed to study the effect of novobiocin on membrane potential and intracellular electrolyte concentrations in the frog skin epithelium. In both species investigated ( Rana esculenta and Rana temporaria), novobiocin (1 mM, outer bath) caused a stimulation of transepithelial Na transport, a depolarization of apical membrane potential, a fall in the apical fractional resistance, and an increase in the intracellular Na concentration. The rise in the Na concentration was accompanied by an equivalent fall in the K concentration. All effects of novobiocin were fully reversible by subsequent application of amiloride. The depolarization as well as the Na increase suggests that the natriferic effect of novobiocin is due to a stimulation of the apical Na influx. Combining both measurements it was possible to calculate the effect of novobiocin on the Na permeability of the apical membrane directly. In Rana esculenta novobiocin increased the permeability from 4.5 to 23.2 nm/s. In Rana temporaria the increase was significantly smaller, from 8.7 to 16.9 nm/s. The transport rate as measured by the short-circuit current showed a non-linear dependence on the apical Na permeability. In the range of transport rates normally encountered, however, the current was a linear function of the Na permeability consistent with the view that the apical membrane is rate-limiting in transepithelial Na transport. [ABSTRACT FROM AUTHOR]

The present study has been performed to test for the influence of serotonin on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK)-cells. Under control conditions PD averages −48.6±0.6 mV ( n=98). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +6.3±0.6 mV ( n=6) and +14.1±1.0 mV ( n=12), respectively. The cell membrane is transiently hyperpolarized to −67.8±0.8 mV ( n=63) by 1 μmol/l serotonin. In the presence of serotonin, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +26.4±1.0 mV ( n=11). 1 mmol/l barium depolarizes the cell membrane by +15.7±1.3 mV ( n=17) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, serotonin leads to a transient hyperpolarization by −26.3±1.0 mV ( n=16). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. 10 μmol/l methysergide hyperpolarize the cell membrane by −7.2±2.0 mV ( n=6). In the presence of 10μmol/l methysergide, the effect of serotonin is virtually abolished (+0.4±0.9 mV, n=6). 1 μmol/l ketanserin, a 5-HT receptor blocking agent, ICS 205-930, a 5-HT receptor blocking agent, and phentolamine, an unspecific α-receptor blocking agent, do not significantly modify the effect of serotonin. In the nominal absence of extracellular calcium, the effect of serotonin is markedly reduced. In conclusion, serotonin hyperpolarizes MDCK-cells by increasing apparent potassium conductance. This effect is transmitted by 5-HT receptors and depends on extracellular calcium. [ABSTRACT FROM AUTHOR]

In the present study we have investigated the influence of bradykinin on the potential difference across the cell membrane (PD) of Madin Darby Canine Kidney (MDCK)-cells. In the absence of bradykinin PD averages −52.6±0.9 mV ( n=52). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +5.2±0.3 mV ( n=8) and +14.9±1.0 mV ( n=9), respectively. The application of 0.1 μmol/l bradykinin leads to a transient hyperpolarization of the cell membrane to −70.3±0.6 mV ( n=30). During this transient hyperpolarization increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +10.4±0.7 mV ( n=10) and +29.2±0.8 mV ( n=8) respectively. Application of fragments of bradykinin (0.1 μmol/l) are without significant effect on the potential difference across the cell membrane. 1 mmol/l barium depolarizes the cell membrane by +15.8±1.2 mV ( n=9) and abolishes the effect of step increase of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, bradykinin leads to a transient hyperpolarization by −24.7±1.3 mV ( n=7). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. In the nominal absence of extracellular calcium, bradykinin leads to a transient hyperpolarization, which can be elicited only once. The transient hyperpolarization is not affected by the presence of verapamil or indomethacin. In conclusion, bradykinin hyperpolarizes MDCK-cells by increasing the apparent potassium conductance. This effect is probably mediated by increase of intracellular calcium activity. [ABSTRACT FROM AUTHOR]

The present study has been performed, to test for the influence of epinephrine on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK) cells. Under control conditions, mimicking the in vivo situation, PD averages −53.3±0.9 mV ( n=37). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +4.3±0.4 mV ( n=5) and +15.8±1.2 mV ( n=5), respectively. The application of 1 μmol/l epinephrine leads to sustained hyperpolarization of the cell membrane to −71.5±0.7 mV ( n=37). In the presence of epinephrine, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +30.6 ±0.2 mV ( n=5); 1 mmol/l barium depolarizes the cell membrane by +14.8±0.7 mV ( n=20) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, epinephrine leads to a transient hyperpolarization by −31.2 ±1.2 mV ( n=18). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium; 10 μmol/l verapamil depolarizes the cell membrane to −41.0±2.6 mV ( n=11). In the presence of verapamil, the hyperpolarizing effect of epinephrine is only transient; 10 μmol/l phentolamine depolarizes the cell membrane by +3.0±0.6 mV ( n=8). In the presence of phentolamine, the effect of epinephrine is virtually abolished (+0.4±0.6 mV, n=8); 1 μmol/l isoproterenol depolarizes the cell membrane by +2.8±0.8 mV ( n=8). In the norminal absence of extracellular calcium, epinephrine leads to a transient hyperpolarization, which can only be elicited once. In conclusion, cpinephrine hyperpolarizes MDCK cells by increasing the apparent potassium conductance. This effect is transmitted by α-receptors and may be mediated by increases of intracellular calcium activity. [ABSTRACT FROM AUTHOR]

To gain some insight into electrogenic transport processes across the plasma membrane of Madin-Darby canine kidney (MDCK)-cells, continuous measurements of the potential difference across the plasma membrane (PD) were made during step changes of extracellular ion composition as well as application of barium or valinomycin. During control conditions mimicking in vivo extracellular fluid, PD approaches −51.5±0.8 mV ( n=62). Step increase of extracellular potassium concentration from 5.4 to 10, to 20 or to 35 mmol/l, depolarizes PD by +5.5±0.8 mV ( n=7), by +15.8±0.5 mV ( n=64) and by +23.8±1.2 mV ( n=12), respectively. 1 mmol/l barium depolarizes PD by +19.8±0.6 mV ( n=38) and abolishes the effect of increasing extracellular potassium from 5.4 to 10 mmol/l but not to 35 mmol/l. Ten μmol/l valinomycin hyperpolarizes PD to −69.3±2.9 mV ( n=7). In the presence of valinomycin, increase of extracellular potassium from 5.4 to 20 mmol/l depolarizes PD by +31.0±1.0 mV ( n=7). Ouabain depolarizes PD and reduces the sensitivity of PD to extracellular potassium concentration. Omission of extracellular bicarbonate and carbondioxide as well as increase of extracellular bicarbonate at constant carbondioxide lead to a hyperpolarization and enhanced sensitivity of PD to extracellular potassium. In the presence of barium, the effects of omitted bicarbonate and carbondioxide are only transient. In conclusion, the plasma membrane of MDCK-cells is highly conductive to potassium. At low but not at high extracellular potassium concentrations the potassium conductance can be blocked by barium. The potassium conductance can further be reduced by ouabain as well as acidosis and enhanced by alkalosis as well as omission of extracellular carbondioxide and bicarbonate. [ABSTRACT FROM AUTHOR]