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

Gasotransmitter hydrogen sulphide (H 2 S) has emerged as a regulator of multiple physiological and pathophysiological processes throughout. Here, we have investigated the effects of NaHS (fast donor of H 2 S) and GYY4137 (GYY, slow donor of H 2 S) 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 Ca 2+ entry through voltage-activated Ca 2+ channels (VACCs) because, in fact, NaHS and GYY caused a mild inhibition of whole-cell Ca 2+ currents. Rather, the facilitation of exocytosis seemed to be associated to an augmented basal [Ca 2+ ] c and the K + -elicited [Ca 2+ ] c transients; such effects of H 2 S donors are aborted by cyclopiazonic acid (CPA), that causes endoplasmic reticulum (ER) Ca 2+ 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 Ca 2+ 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 Ca 2+ handling by the ER and mitochondria. On the basis of these results, we propose that H 2 S regulates catecholamine secretory responses triggered by K + in BCCs by (i) mobilisation of ER Ca 2+ and (ii) interference with mitochondrial Ca 2+ circulation. In so doing, the clearance of the [Ca 2+ ] c transient will be delayed and the Ca 2+ -dependent trafficking of secretory vesicles will be enhanced to overfill the secretory machinery with new vesicles to enhance exocytosis.