CONTRIBUTION OF EXTRACELLULAR CALCIUM TO INTRACELLULAR PH-INDUCED CHANGES IN SPONTANEOUS FORCE OF RAT PORTAL-VEIN

Normal spontaneous mechanical activity of isolated rat portal vein is critically dependent on external calcium as a source of contractile activation and this force is mollified by alteration of intracellular pH. We have studied the involvement of the extracellular calcium pool in intracellular pH-induced changes in force. Intracellular pH was changed, at constant external pH, by NH4Cl application and withdrawal in bathing [CaCl2]varying between 3 and 0 mM, and manoeuvres were performed in the presence and absence of either the intracellular calcium mobilizer caffeine or the calcium channel blocker nifedipine. The results indicate that alteration of spontaneous force with intracellular pH has an absolute requirement for calcium entry from outside and calcium release from caffeine-sensitive intracellular stores.