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Effect of stimulation and veratrine on total cellular calcium in rat and guinea-pig ventricular myocytes

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Summary

In rat cardiac myocytes, calcium efflux by Na+/Ca2+-exchange is expected only during ventricular systole following initial action potential repolarization. In contrast, in guinea-pigs, calcium influx via Na+/Ca2+-exchange is expected only during the initial portion of the action potential. Thus electrical stimulation is expected to result in reduced intracellular calcium ([Ca2+]i) in rat and an increase in guinea pig. We tested this hypothesis by measuring total cellular calcium ([Ca]tot) using45Ca following stimulation of isolated rat and guinea-pig ventricular myocytes. Many studies have also emphasized that the rate and the direction of Na+/Ca2+-exchange across the sarcolemma are in part dependent on the magnitude of the transsarcolemmal sodium gradient. Thus, increasing intracellular sodium ([Na+]i) is expected to result in an increased [Ca2+]i. This hypothesis was also tested by measuring [Ca]tot following veratrine administration. Enzymatically isolated rat and guinea-pig ventricular myocytes were divided into two groups; non-stimulated and stimulated (1 Hz). The concentration-dependent effects of veratrine (1,10,100 μg/ml) on [Ca]tot were determined in both these groups. In the absence of veratrine, non-stimulated rat myocytes had a significantly higher [Ca]tot than did stimulated ones. Non-stimulated guinea-pig myocytes had a significantly lower [Ca]tot when compared with stimulated ones Veratrine increased [Ca]tot in both species in a concentration-dependent fashion. In addition, following veratrine the difference between [Ca]tot in non-stimulated and stimulated rat myocytes was no longer significant. These results support those of others who have demonstrated that stimulation is associated with a gain of cellular calcium in both rabbit and guinea-pig ventricle and a calcium loss in rat ventricle. In addition, the increase in [Ca]tot following veratrine was similar to the results of others that have shown an increase in [Ca2+]i following exposure to veratrum alkaloids. Thus, we have demonstrated, using a technique limited to determination of [Ca]tot, that this parameter may reflect changes produced by alteration of Na+/Ca2+-exchange.

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  1. T. Henden

    Present address: Department of Medical Physiology, Institute of Medical Biology, University of Tromsø, 9037, Tromsø, Norway

Authors and Affiliations

  1. Department of Medical Physiology, Institute of Medical Biology, University of Tromsø, 9037, Tromsø, Norway

    T. S. Larsen & D. A. Lathrop

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  2. T. S. Larsen
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Henden, T., Larsen, T.S. & Lathrop, D.A. Effect of stimulation and veratrine on total cellular calcium in rat and guinea-pig ventricular myocytes. Basic Res Cardiol 88, 557–565 (1993). https://doi.org/10.1007/BF00788874

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  • DOI: https://doi.org/10.1007/BF00788874

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