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Effects of Lead Ions on Events Associated with Exocytosis in Isolated Bovine Adrenal Medullary Cells
Author(s) -
Pocock G.,
Simons T. J. B.
Publication year - 1987
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1987.tb04104.x
Subject(s) - exocytosis , adrenal medulla , chromaffin cell , chemistry , medullary cavity , ion , endocrinology , medicine , microbiology and biotechnology , biology , catecholamine , secretion , organic chemistry
Lead buffers (citrate and Tiron) were used to investigate the effects of low concentrations (0.1–6 μ M ) of Pb 2+ on stimulus‐secretion coupling in isolated bovine chromaffin cells. Nicotinic agonists and high K elicit secretion by enhancing Ca 2+ influx into chromaffin cells. Pb 2+ inhibited the catecholamine secretion in response to 500 μ M carbachol and 77 m M K + depolarization but was without significant effect on basal secretion. Pb 2+ also inhibited the influx of 45 Ca occurring in response to these agents. The K 0.5 values for inhibition suggest that the carbachol‐evoked flux is more sensitive to Pb 2+ than influx in response to a direct depolarization. When extracellular calcium was lowered in the absence of Pb 2+ , both secretion and 45 Ca entry were reduced. The effects of Pb 2+ were comparable to those of lowered Ca 2+ . 22 Na influx through nicotinic receptor‐mediated channels, measured in the presence of tetrodotoxin (2 μ M ) and ouabain (50 μ M ), was inhibited by Pb 2+ . The results suggest that Pb 2+ inhibits exocytotic catecholamine secretion by inhibiting Ca 2+ influx. The differential sensitivity to Pb 2+ of K‐ and carbachol‐evoked 45 Ca flux, coupled with the 22 Na measurements, indicates that Pb 2+ inhibits the movement of ions through acetylcholine‐induced channels as well as through voltage‐sensitive calcium channels.