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 approximate to 30 pS nonselectiv e cation channel (NSC channel) was studied by the patch-clamp techniqu e in inside-out patches obtained from rat brown-fat cells. NSC channel activity was induced by excision; reduced redox state induced by dith iothreitol accelerated the kinetics in the excised state. The NSC chan nels were inhibited by the fenamates flufenamic acid and mefenamic aci d but not by NS-1619 or SKF-96365, The channels were inhibited by puri ne nucleotides but not by polyamines, No evidence for protein kinase C , CaM kinase or protein kinase A activation of the NSC channel was obt ained. NSC-channel activity was stimulated in a concentration-dependen t manner by Ca2+ but the EC50 was very high (0.81 mM), in comparison t o expected cytosolic Ca2+ levels, In the presence of ATP, even higher Ca2+ levels were necessary for comparable NSC-channel activation. The increase in P-o was not associated with an increase in open-time const ants, We conclude that although high Ca2+ levels can experimentally ac tivate the NSC channel, a further mediatory step must probably be post ulated in order to link alpha(1)-adrenergic stimulation to NSC-channel activation.