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

• Published in: Basic research in cardiology Vol. 88; no. 6; pp. 557 - 565
• Main Authors: HENDEN, T, LARSEN, T. S, LATHROP, D. A
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-11-1993
• Subjects: Animals; Biological and medical sciences; Calcium - metabolism; Electric Stimulation; Female; Fundamental and applied biological sciences. Psychology; Guinea Pigs - metabolism; Heart; Heart Ventricles; Male; Myocardium - cytology; Myocardium - metabolism; Osmolar Concentration; Rats; Rats, Sprague-Dawley; Veratrine - pharmacology; Vertebrates: cardiovascular system; Heart; Calcium; Rat; Rodentia; Heart ventricle; Myocyte; Vertebrata; Mammalia; Guinea pig; Sodium; Animal; Circulatory system; Biological effect; Ion exchange
• ISSN: 0300-8428; 1435-1803
• DOI: 10.1007/BF00788874

In rat cardiac myocytes, calcium efflux by Na+/Ca(2+)-exchange is expected only during ventricular systole following initial action potential repolarization. In contrast, in guinea-pigs, calcium influx via Na+/Ca(2+)-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) using 45Ca following stimulation of isolated rat and guinea-pig ventricular myocytes. Many studies have also emphasized that the rate and the direction of Na+/Ca(2+)-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 micrograms/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.