A muscarinic receptor agonist mobilizes Ca2+ from caffeine and inositol-1,4,5-trisphosphate-sensitive Ca2+ stores in cat adrenal chromaffin cells.

To gain some understanding of the characteristics of intracellular Ca2+ stores of cat adrenal chromaffin cells, we investigated the effects of ryanodine, a blocker of Ca(2+)-induced Ca2+ release channels in muscle, on both cytosolic Ca2+ concentration and catecholamine secretion induced by caffeine or methacholine. The results suggest that Ca2+ stores consist of at least two compartments, one which is sensitive to both caffeine and inositol-1,4,5-trisphosphate (IP3), and the other which is sensitive to IP3 alone.