Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

11-POS Board 4 PACAP-MEDIATED REGULATION OF CHROMAFFIN CELL SECRETION

Nicole A. Bell ; Xiaohuan Chen 1 ; Arun Anantharam 1 ; David Giovannucci 1 ; 1 University of Toledo College of Medicine, Neurosciences, Toledo, OH, USA

Splanchnic nerve input to adrenomedullary chromaffin cells evokes calcium-triggered secretion of norepinephrine and epinephrine into the bloodstream to contribute to the regulation of the body’s physiological sympathetic stress response. The neurotransmitters, acetylcholine and pituitary adenylate cyclase-activating polypeptide (PACAP), are known to be critical for inducing chromaffin cell secretion. However, the mechanism by which PACAP regulates exocytotic activity is not well understood. We explored potential mechanisms by which PACAP induced the exocytotic release of catecholamine from primary cultured mouse chromaffin cells using patch-clamp methods. PACAP application was found to activate a small inward current in a rapid and a concentration-dependent manner. In 47% of chromaffin cells tested, 500 nM PACAP application evoked a current with an average peak amplitude of 21.8 pA ±5.0 pA. The observed current was dependent on extracellular calcium and diminished in the presence of 10 μM nifedipine. In other work from our group, PACAP was shown to evoke PLCε -dependent inositol 1,4,5-trisphosphate receptor-mediated calcium release from intracellular stores and this release was dependent on the presence of external calcium, reduced by nifedipine, and required to support PACAP-induced exocytotic activity. This suggested that PACAP induced increases in intracellular calcium and the concomitant activation of protein kinase C (PKC) may regulate the number of available secretory granules to facilitate exocytotic activity. Using time-resolved membrane capacitance measurements in combination with perforated patch clamp methods, we showed that PACAP treatment increased the readily releasable pool size as determined by two pulse step depolarizations or trains of step depolarizations. Ongoing studies using pharmacological and genetic approaches will elucidate the mechanism by which PACAP mediated calcium influx and intracellular calcium release effects the readily releasable pool size and provide new insights into how splanchnic signaling tunes the neuroendocrine stress response.

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