The effect of substances releasing intracellular calcium ions on sodium-dependent calcium efflux from guinea-pig auricles.
1. 45-Ca efflux and resting tension were measured in isolated guinea-pig auricles under conditions known to change the intracellular free Ca ion concentration. 2. In the presence of [Na]o, caffeine (2mM) increases 45-Ca efflux, but does not produce a contracture, while in the absence of [Na]o and [Ca]o caffeine causes a contracture without increasing 45-Ca efflux. Adrenaline (10-minus5-10-minus 4M) with or without theophylline (0-5-1-0mM) has no effect on either 45-Ca efflux or resting tension. 3. In the presence of caffeine the rate of net efflux of Ca depends on [Na]o-2. Caffeine contractures of muscles in Na-free solution relax upon the addition of [Na]o. Relaxation is correlated with the increase in net efflux of Ca. 4. Cyanide (2mM) produces a variable increase in 45-Ca efflux without a concomitant contracture in Na-containing solutions, but in Na, Ca-free solutions a large contracture occurs without significant increase in 45-Ca efflux. 5. A large increase in 45-Ca efflux and a contracture were observed with the 'Ca-ionophore' X 537 A. 6. Changes in membrane potential (K-depolarization) in hypertonic solutions have no significant effect on Na-dependent 45-Ca efflux, which is an agreement with an electroneutral 2:1 Na-Ca exchange. 7. Cyanide and X 537 A both cause a considerable release of Ca ions from isolated guinea-pig heart mitochondria, while caffeine has no effect. 8. The results suggest a powerful role of the Na-Ca exchange system in reducing the intracellular Ca concentration after Ca release from intracellular stores.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002132:Calcium Radioisotopes; D006168:Guinea Pigs; D006325:Heart Atria / Q000378:metabolism; D066298:In Vitro Techniques; D007832:Lasalocid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000502:physiology
D002132:Calcium Radioisotopes; D002110:Caffeine; D012964:Sodium; D011188:Potassium; D002118:Calcium; D007832:Lasalocid