Beta(3)-adrenergic stimulation and insulin inhibition of non-selective cation channels in white adipocytes of the rat.
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 (high K(+), no Ca(2+) 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/microm(2). It was blocked by TEA (IC(50)=1.5 mM). A Ca(2+)-activated non-selective cation channel (NSC-channel) appeared at a mean density of 1/microm(2) in inside-out patches ([Ca(2+)](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 microM propranolol even 1 microM 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.
Ringer
E
E
Department of Zoology, University of Regensburg, D-93040 Regensburg, Germany.
Russ
U
U
Siemen
D
D
D000255:Adenosine Triphosphate / Q000494:pharmacology; D017667:Adipocytes / Q000502:physiology*; D000273:Adipose Tissue / Q000166:cytology / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D051668:Delayed Rectifier Potassium Channels; D007444:Inulin / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology; D019789:Tetraethylammonium / Q000494:pharmacology*
D000318:Adrenergic beta-Agonists; D051668:Delayed Rectifier Potassium Channels; D007473:Ion Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011943:Receptors, Adrenergic, beta; D022702:Receptors, Adrenergic, beta-3; D018047:Receptors, Purinergic P1; D019789:Tetraethylammonium; D000255:Adenosine Triphosphate; D007444:Inulin; D007545:Isoproterenol; D002118:Calcium; D009638:Norepinephrine