Nystatin perforated-patch clamp and single-channel recording methods were used to characterize macroscopic and single-channel K+ currents and the effects of angiotensin II (AngII) in cultured rat adrenal glomerulosa cells. Two basic patterns of macroscopic current-voltage relationships were observed: type 1 exhibited a rapidly activating, noninactivating, voltage-dependent outward current and type 2 exhibited an inactivating voltage-dependent outward current attributed to charybdotoxin sensitive Ca++-dependent K+ channels. Most cells exhibited the type 1 pattern and experiments focused on this cell type. Cell-attached and inside-out patches were dominated by a single K+ channel class which exhibited an outward conductance of 12 pS (20 mm K+ pipette in cell-attached and inside-out configurations, 145 mm K+ in), a mean open time of 2 msec, and a weakly voltage-dependent low open probability that increased with depolarization. Channel open probability was reversibly inhibited by bath stimulation with AngII. At the macroscopic level, type 1 cell macroscopic K+ currents appeared comprised of two components: a weakly voltage-dependent current controlling the resting membrane potential (−85 mV) which appeared mediated by the 12 pS K+ channel and a rapidly activating, noninactivating voltage-dependent current activated above −50 mV. The presence of the second voltage-dependent K+ channel class was suggested by the effects of AngII, the blocking effects of quinidine and Cs+, and the properties of the weakly voltage-dependent K+ channel described. The K+ selectivity of the macroscopic current was demonstrated by the dependence of current reversal potentials on the K+ equilibrium potential and by the effects of K+ channel blockers, Cs+ and quinidine. AngII (10 pm to 1 nm) reversibly inhibited macroscopic K+ currents and this effect was blocked by the AT1 receptor antagonist losartin.
The Journal of Membrane Biology – Springer Journals
Published: Apr 1, 1997
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