Histamine-induced Ca2+ release in bovine adrenal chromaffin cells

The histamine-induced biphasic increase of the intracellular free [Ca2+] ([Ca2+]i) was studied in bovine adrenal chromaffin cells using fura-2 microfluorimetry and the whole-cell patch-clamp technique. Both the rapid, transient Ca2+ rise and the sustained plateau component of elevated [Ca2+]i were independent of extracellular Ca2+. Incubation with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) blocker thapsigargin diminished histamine-induced changes in [Ca2+]i. When Ca2+ release was either stimulated by IP3 or blocked with the competitive inhibitor heparin, histamine was unable to elicit the typical Ca2+ rise. Ryanodine, tetracaine and ruthenium red, all blockers of Ca2+ release from caffeine-sensitive stores, had only minor effects on the agonist-induced Ca2+ changes. The contribution of mitochondria in shaping the histamine-induced Ca2+ increase was studied using ruthenium red and the two proton ionophores carbonylcyanide m-chlorophenylhydrazone (CCCP) and carbonylcyanide p-(trifluoromethoxy)phenylhydrazone (FCCP). Both mitochondrial uncouplers reversibly increased [Ca2+]i and induced an inward current leading to cell membrane depolarisation. In summary, these results indicate that Ca2+ from IP3-sensitive stores is essential for the generation of both the transient increase and secondary elevation in [Ca2+]i.