Chromaffin cell action potentials and their possible role in adrenaline secretion from rat adrenal medulla.

Abstract

SUMMARY1. The role of action potentials in adrenaline secretion was investigated in the rat adrenal medulla. The effects of various treatments on adrenaline secretion from the perfused adrenal medulla were compared with the effects of similar treatments on spike frequency in dissociated adrenal chromaffin cells.2. KCl concentrations between 10 and 20 mm increased the extracellularly recorded spike frequency of dissociated adrenal chromaffin cells. Upon perfusion by a KCl concentration of 30 mM there was an initial brief burst of spikes followed by a period of inactivity in the continued presence of 30 mM-KCl. Tetrodotoxin (TTX, 6/M) decreased the amplitude and frequency of the KCl evoked spikes.3. The rate of adrenaline secretion from the isolated perfused rat adrenal gland increased as the KCl concentration was raised to 10 and up to 120 mm. Secretion which was evoked by KCl concentrations between 10 and 20 mm was partially inhibited by TTX. At KCl concentrations of 30 mm or greater evoked secretion was no longer affected by TTX.4. CoCl2 (5 mM) blocked KCl increase of spike frequency and also blocked stimulation of adrenaline secretion by all concentrations of KCl tested.5. Tetraethylammonium chloride (10 mM), which decreased spike frequency but greatly prolonged the spike duration, enhanced secretion induced by 15 mM-KCl.6. The results are consistent with the following interpretation. The TTX insensitive portion of the KCl stimulated adrenaline secretion is due to Ca influx through voltage dependent Ca channels which are open as a consequence of the steady-state level of KCl depolarization. The TTX sensitive portion of secretion is indicative of an extra increment of Ca influx during spike activity enhanced by KCl. This increment of Ca influx may occur through voltage dependent Ca channels whose activation is facilitated by the voltage changes caused during the TTX sensitive Na component of the spike and possibly through the Na channel itself.7. Stimulation of secretion by acetylcholine (ACh) in the perfused adrenal medulla was half maximal at 15 /LM and began to saturate around

Dynamin I plays dual roles in the activity-dependent shift in exocytic mode in mouse adrenal chromaffin cells

“…Under low frequency APe stimulation matching splanchnic firing under basal sympathetic tone (0.5 Hz) [39][40][41], we show that transfection with a peptide fragment of the Dynamin I prolinerich domain (PRD) that competitively competes for binding to amphiphysin [17] has the result of blocking granule endocytosis. Consistent with previous work [4,19,25], disrupting clathrinmediated endocytosis by blocking synaptojanin/endophilin binding has no effect on membrane retrieval in these conditions.…”

Pharmacological evidence for the possible involvement of repetitive action potentials in facilitation by GABA of catecholamine secretion in bovine adrenal chromaffin cells

“…An electrophysiological study demonstrated the presence of several types of K+ channels in chromaffin cells and its inhibition by TEA (Marty & Neher, 1985). Further, Kidokoro & Ritchie (1980) explained the stimulatory action of TEA on KCI-induced CA secretion with regard to the action potential, and suggested that TEA is only effective on the portion of CA secretion which is mediated by spike activity. The present study demonstrated that the enhancement by TEA of GABA-evoked CA secretion was inhibited by TTX and removal of extracellular Na+.…”

Myosin II Activation and Actin Reorganization Regulate the Mode of Quantal Exocytosis in Mouse Adrenal Chromaffin Cells

“…We used amperometry to quantify the kinetics of catecholamine release from cells stimulated with APe voltage templates delivered at 0.5 or 15 Hz in perforated-patch voltage clamp. These conditions mimic splanchnic input under sympathetic tone or acute stress, respectively (Kidokoro and Ritchie, 1980;Chan and Smith, 2001;Wilson et al, 2002).…”

“…This exocytic mode is characterized by transient fusion of the granule with the cell membrane, maintenance of basic granule morphology, and retention of the dense proteinaceous granule core (Fulop et al, 2005). In contrast, under acute stress, increased splanchnic firing and subsequent acetylcholine release drive chromaffin cells to increase their activity level (Brandt et al, 1976;Kidokoro and Ritchie, 1980), resulting in elevated catecholamine output. Under these conditions, the restricted fusion pore dilates, leading to a full granule collapse and expulsion of both catecholamine and the neuropeptide-containing proteinaceous core (Rahamimoff and Fernandez, 1997;Fulop et al, 2005).…”