Regulation of the activity of 27 pS nonselective cation channels in excised membrane patches from rat brown-fat cells.
The regulation of the activity of the approximately 30 pS nonselective cation channel (NSC channel) was studied by the patch-clamp technique in inside-out patches obtained from rat brown-fat cells. NSC channel activity was induced by excision; reduced redox state induced by dithiothreitol accelerated the kinetics in the excised state. The NSC channels were inhibited by the fenamates flufenamic acid and mefenamic acid but not by NS-1619 or SKF-96365. The channels were inhibited by purine nucleotides but not by polyamines. No evidence for protein kinase C, CaM kinase or protein kinase A activation of the NSC channel was obtained. NSC-channel activity was stimulated in a concentration-dependent manner by Ca2+ but the EC50 was very high (0.81 mM), in comparison to expected cytosolic Ca2+ levels. In the presence of ATP, even higher Ca2+ levels were necessary for comparable NSC-channel activation. The increase in Po was not associated with an increase in open-time constants. We conclude that although high Ca2+ levels can experimentally activate the NSC channel, a further mediatory step must probably be postulated in order to link alpha1-adrenergic stimulation to NSC-channel activation.
Koivisto
A
A
The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, Stockholm, Sweden. Ari-Pekka.Koivisto@utu.fi
Klinge
A
A
Nedergaard
J
J
Siemen
D
D
D002001:Adipose Tissue, Brown / Q000378:metabolism / Q000502:physiology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004229:Dithiothreitol / Q000494:pharmacology; D004594:Electrophysiology; D005439:Flufenamic Acid / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008528:Mefenamic Acid / Q000494:pharmacology; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D011494:Protein Kinases / Q000378:metabolism; D011685:Purine Nucleotides / Q000494:pharmacology; D051381:Rats
D000316:Adrenergic alpha-Agonists; D001562:Benzimidazoles; D007093:Imidazoles; D007473:Ion Channels; D011685:Purine Nucleotides; C086491:NS 1619; D008528:Mefenamic Acid; D005439:Flufenamic Acid; D011494:Protein Kinases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium; D004229:Dithiothreitol