Hydrogen sulphide facilitates exocytosis by regulating the handling of intracellular calcium by chromaffin cells.

Abstract

Gasotransmitter hydrogen sulphide (H2S) has emerged as a regulator of multiple physiological and pathophysiological processes throughout. Here, we have investigated the effects of NaHS (fast donor of H2S) and GYY4137 (GYY, slow donor of H2S) on the exocytotic release of catecholamines from fast-perifused bovine adrenal chromaffin cells (BCCs) challenged with sequential intermittent pulses of a K+-depolarizing solution. Both donors caused a concentration-dependent facilitation of secretion. This was not due to an augmentation of Ca2+ entry through voltage-activated Ca2+ channels (VACCs) because, in fact, NaHS and GYY caused a mild inhibition of whole-cell Ca2+ currents. Rather, the facilitation of exocytosis seemed to be associated to an augmented basal [Ca2+]c and the K+-elicited [Ca2+]c transients; such effects of H2S donors are aborted by cyclopiazonic acid (CPA), that causes endoplasmic reticulum (ER) Ca2+ depletion through sarcoendoplasmic reticulum Ca2+ ATPase inhibition and by protonophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), that impedes the ability of mitochondria to sequester cytosolic Ca2+ during cell depolarization. Inasmuch as CPA and FCCP reversed the facilitation of secretion triggered by K+ in the presence of NaHS and GYY, is seems that such facilitation is tightly coupled to Ca2+ handling by the ER and mitochondria. On the basis of these results, we propose that H2S regulates catecholamine secretory responses triggered by K+ in BCCs by (i) mobilisation of ER Ca2+ and (ii) interference with mitochondrial Ca2+ circulation. In so doing, the clearance of the [Ca2+]c transient will be delayed and the Ca2+-dependent trafficking of secretory vesicles will be enhanced to overfill the secretory machinery with new vesicles to enhance exocytosis.