Abstract
Single-channel currents were recorded from the plasma membrane of white adipocytes of 6-8-week-old male Sprague-Dawley rats. In outside-out patches thigh K+, no Ca2+ in pipette), a voltage-dependent K-channel (delayed rectifier) with a single-channel conductance (gamma) of 16 pS (24 degrees C) in modified Ringer's was active at a density of 0.5/mu m(2). It was blocked by TEA (IC50 = 1.5 mM). A ...
Abstract
Single-channel currents were recorded from the plasma membrane of white adipocytes of 6-8-week-old male Sprague-Dawley rats. In outside-out patches thigh K+, no Ca2+ in pipette), a voltage-dependent K-channel (delayed rectifier) with a single-channel conductance (gamma) of 16 pS (24 degrees C) in modified Ringer's was active at a density of 0.5/mu m(2). It was blocked by TEA (IC50 = 1.5 mM). A Ca2+-activated non-selective cation channel (NSC-channel) appeared at a mean density of 1/mu m(2) in inside-out patches ([Ca2+](i) = 1.2 mM). gamma was 28 pS (24 degrees C). The NSC showed weak voltage dependence and was blocked by mefenamic acid and by internal ATP. In the cell-attached mode spontaneous activity could be blocked reversibly by 100 nM insulin. Noradrenaline (NA, 100 nM) induced a flickering activity of the NSC-channels. Isoproterenol (100 nM) caused activity of the NSC-channel as well. After 1 mu M propranolol even 1 mu M NA did not induce any activity. The alpha-antagonist phentolamine had no effect on isoproterenol- or on NA-induced currents. The beta(3)-agonists BRL 37344 and BRL 35135A induced activity of the NSC-channel at 100 nM as well. We conclude that white adipocytes express ion channels which are comparable to those in brown adipocytes and that beta-receptor activation opens NSC-channels thus allowing for Na+ entry into white adipocytes. (C) 2000 Elsevier Science B.V. All rights reserved.
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