Endotoxemia Enhances Catecholamine Secretion From Male Mouse Adrenal Chromaffin Cells Through an Increase In Ca2+ Release From the Endoplasmic Reticulum

Abstract

Enhanced epinephrine secretion from adrenal chromaffin cells (ACCs) is an important homeostatic response to severe systemic inflammation during sepsis. Evidence suggests that increased activation of ACCs by preganglionic sympathetic neurons and direct alterations in ACC function contribute to this response. However, the direct effects of sepsis on ACC function have yet to be characterized. We hypothesized that sepsis enhances epinephrine secretion from ACCs by increasing intracellular Ca2+ signaling. Plasma epinephrine concentration was increased 5-fold in the lipopolysaccharide-induced endotoxemia model of sepsis compared with saline-treated control mice. Endotoxemia significantly enhanced stimulus-evoked epinephrine secretion from isolated ACCs in vitro. Carbon fiber amperometry revealed an increase in the number of secretory events during endotoxemia, without significant changes in spike amplitude, half-width, or quantal content. ACCs isolated up to 12 hours after the induction of endotoxemia exhibited larger stimulus-evoked Ca2+ transients compared with controls. Similarly, ACCs from cecal ligation and puncture mice also exhibited enhanced Ca2+ signaling. Although sepsis did not significantly affect ACC excitability or voltage-gated Ca2+ currents, a 2-fold increase in caffeine (10 mM)-stimulated Ca2+ transients was observed during endotoxemia. Depletion of endoplasmic reticulum Ca2+ stores using cyclopiazonic acid (10 μM) abolished the effects of endotoxemia on catecholamine secretion from ACCs. These findings suggest that sepsis directly enhances catecholamine secretion from ACCs through an increase in Ca2+ release from the endoplasmic reticulum. These alterations in ACC function are likely to amplify the effects of increased preganglionic sympathetic neuron activity to further enhance epinephrine levels during sepsis.