E. Ringer et al., beta(3)-adrenergic stimulation and insulin inhibition of non-selective cation channels in white adipocytes of the rat, BBA-BIOMEMB, 1463(2), 2000, pp. 241-253
Single-channel currents were recorded from the plasma membrane of white adi
pocytes of 6-8-week-old male Sprague-Dawley rats. In outside-out patches th
igh K+, no Ca2+ in pipette), a voltage-dependent K-channel (delayed rectifi
er) with a single-channel conductance (gamma) of 16 pS (24 degrees C) in mo
dified Ringer's was active at a density of 0.5/mu m(2). It was blocked by T
EA (IC50 = 1.5 mM). A Ca2+-activated non-selective cation channel (NSC-chan
nel) 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 d
ependence and was blocked by mefenamic acid and by internal ATP. In the cel
l-attached mode spontaneous activity could be blocked reversibly by 100 nM
insulin. Noradrenaline (NA, 100 nM) induced a flickering activity of the NS
C-channels. Isoproterenol (100 nM) caused activity of the NSC-channel as we
ll. After 1 mu M propranolol even 1 mu M NA did not induce any activity. Th
e alpha-antagonist phentolamine had no effect on isoproterenol- or on NA-in
duced currents. The beta(3)-agonists BRL 37344 and BRL 35135A induced activ
ity 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+ ent
ry into white adipocytes. (C) 2000 Elsevier Science B.V. All rights reserve
d.