Gap junctions mediate electrical signaling and ensuing cytosolic Ca2+ increases between chromaffin cells in adrenal slices: A role in catecholamine release

Abstract

In adrenal chromaffin cells, a rise in cytosolic calcium concentration ([Ca2+]i) is a key event in the triggering of catecholamine exocytosis after splanchnic nerve activation. Action potential- or nicotine-induced [Ca2+]i transients are well described in individual chromaffin cells, but whether they remain spatially confined to the stimulated cell or propagate to adjacent cells is not yet known. To address this issue, the spatiotemporal organization of electrical and associated Ca2+ events between chromaffin cells was investigated using the patch-clamp technique and real-time confocal imaging in rat acute adrenal slices. Spontaneous or electrically evoked action potential-driven [Ca2+]i transients were simultaneously detected in neighboring cells. This was likely attributable to gap junction-mediated electrotonic communication, as shown by (1) the bidirectional reflection of voltage changes monitored between cell pairs, (2) Lucifer yellow (LY) diffusion between cells exhibiting spontaneous synchronized [Ca2+]i transients, and (3) the reduction of LY diffusion using the uncoupling agent carbenoxolone. Furthermore, transcripts encoding two connexins (Cx36 and Cx43) were found in single chromaffin cells. This gap junctional coupling was activated after a synaptic-like application of nicotine that mediated synchronous multicellular [Ca2+]i increases. In addition, nicotinic stimulation of a single cell triggered catecholamine release in coupled cells, as shown by amperometric detection of secretory events. Functional coupling between chromaffin cells in situ may represent an efficient complement to synaptic transmission to amplify catecholamine release after synaptic stimulation of a single excited chromaffin cell.