Open AccessNa+ channel inactivation: a comparative study between pancreatic islet -cells and adrenal chromaffin cells in rat
Author(s) -
Xuelin Lou,
Xiao Yu,
X.-K. Chen,
Kailai Duan,
Dong He,
Ang Qu,
Tao Xu,
Zhuan Zhou
Publication year - 2003
Publication title -
journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.034405
Subject(s) - hyperpolarization (physics) , chromaffin cell , membrane potential , endocrinology , enteroendocrine cell , medicine , patch clamp , chemistry , biophysics , electrophysiology , biology , microbiology and biotechnology , adrenal medulla , endocrine system , catecholamine , hormone , organic chemistry , nuclear magnetic resonance spectroscopy
A comparative study was carried out on the inactivation of Na+ channels in two types of endocrine cells in rats, beta-cells and adrenal chromaffin cells (ACCs), using patch-clamp techniques. The beta-cells were very sensitive to hyperpolarization; the Na+ currents increased ninefold when the holding potential was shifted from -70 mV to -120 mV. ACCs were not sensitive to hyperpolarization. The half-inactivation voltages were -90 mV (rat beta-cells) and -62 mV (ACCs). The time constant for recovery from inactivation at -70 mV was 10.5 times slower in beta-cells (60 ms) than in ACCs (5.7 ms). The rate of Na+-channel inactivation at physiological resting potential was more than three times slower in beta-cells than in ACCs. Na+ influx through Na+ channels had no effect on the secretory machinery in rat beta-cells. However, these 'silent Na+ channels' could contribute to the generation of action potentials in some conditions, such as when the cell is hyperpolarized. It is concluded that the fractional availability of Na+ channels in beta-cells at a holding potential of -70 mV is about 15 % of that in ACCs. This value in rat beta-cells is larger than that observed in mouse (0 %), but is smaller than those observed in human or dog (90 %).