title: Na+ channel inactivation: a comparative study between pancreatic islet beta-cells and adrenal chromaffin cells in rat.
abstract: 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 %).
authors.affiliation: Institute of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Xue-Lin
authors.initials: XL
authors.lastname: Lou
authors.forename: Xiao
authors.initials: X
authors.lastname: Yu
authors.forename: Xiao-Ke
authors.initials: XK
authors.lastname: Chen
authors.forename: Kai-Lai
authors.initials: KL
authors.lastname: Duan
authors.forename: Li-Ming
authors.initials: LM
authors.lastname: He
authors.forename: An-Lian
authors.initials: AL
authors.lastname: Qu
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
authors.forename: Zhuan
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D000311:Adrenal Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D007515:Islets of Langerhans / Q000187:drug effects*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D014044:Tolbutamide / Q000494:pharmacology
chemical_list: D026941:Sodium Channel Blockers; D014044:Tolbutamide