Factors influencing free intracellular calcium concentration in quiescent ferret ventricular muscle.

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Abstract
The photoprotein aequorin was injected into cells of ferret papillary muscles to monitor the resting intracellular free Ca concentration ([Ca2+]i). Increasing the external Ca concentration increased both resting [Ca2+]i and tension. The tension and [Ca2+]i both rose to a peak and then declined to a steady-state level which was higher than the control. Similar, but larger, effects were observed if [Ca2+]i was first elevated with strophanthidin. The increase of [Ca2+]i was accomplished by spontaneous oscillations of [Ca2+]i. The effects of external K, D600 [methoxy verapamil], Mn, Co2-induced acidification and the mitochondrial uncoupler FCCP [carbonylcyanide-p-trifluoromethoxyphenylhydrazone] on [Ca2+]i via a Na-Ca exchange mechanism are described. Implications with respect to a metabolism-dependent [Ca2+]i maintaining mechanism are presented.