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J Physiol Volume 548, Number 1, 191-202, April 1, 2003 DOI: 10.1113/jphysiol.2002.034405
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J Physiol (2003), 548.1, pp. 191-202
© Copyright 2003 D 2003 The Physiological Society
DOI: 10.1113/jphysiol.2002.034405

Na+ channel inactivation: a comparative study between pancreatic islet beta-cells and adrenal chromaffin cells in rat

Xue-Lin Lou*†, Xiao Yu*, Xiao-Ke Chen*, Kai-Lai Duan*, Li-Ming He†, An-Lian Qu†, Tao Xu† and Zhuan Zhou*†

*Institute of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China and †Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan 430074, China

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 %).



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