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Am J Physiol Cell Physiol 280: C199-C215, 2001;
0363-6143/01 $5.00
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Vol. 280, Issue 1, C199-C215, January 2001

Properties of ATP-dependent K+ channels in adrenocortical cells

Lin Xu and John J. Enyeart

Department of Neuroscience, Ohio State University, College of Medicine, Columbus, Ohio 43210-1239

Bovine adrenocortical zona fasciculata (AZF) cells express a novel ATP-dependent K+-permeable channel (IAC). Whole cell and single-channel recordings were used to characterize IAC channels with respect to ionic selectivity, conductance, and modulation by nucleotides, inorganic phosphates, and angiotensin II (ANG II). In outside-out patch recordings, the activity of unitary IAC channels is enhanced by ATP in the patch pipette. These channels were K+ selective with no measurable Na+ or Ca2+ conductance. In symmetrical K+ solutions with physiological concentrations of divalent cations (M2+), IAC channels were outwardly rectifying with outward and inward chord conductances of 94.5 and 27.0 pS, respectively. In the absence of M2+, conductance was nearly ohmic. Hydrolysis-resistant nucleotides including AMP-PNP and NaUTP were more potent than MgATP as activators of whole cell IAC currents. Inorganic polytriphosphate (PPPi) dramatically enhanced IAC activity. In current-clamp recordings, nucleotides and PPPi produced resting potentials in AZF cells that correlated with their effectiveness in activating IAC. ANG II (10 nM) inhibited whole cell IAC currents when patch pipettes contained 5 mM MgATP but was ineffective in the presence of 5 mM NaUTP and 1 mM MgATP. Inhibition by ANG II was not reduced by selective kinase antagonists. These results demonstrate that IAC is a distinctive K+-selective channel whose activity is increased by nucleotide triphosphates and PPPi. Furthermore, they suggest a model for IAC gating that is controlled through a cycle of ATP binding and hydrolysis.

potassium channel; adenosine 5'-triphosphate; nucleotide; angiotensin II


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