title: An ATP-regulated and pH-sensitive inwardly rectifying K(+) channel in cultured human proximal tubule cells.
abstract: Although renal K(+) channels along the nephron have been explored in various animal species, little is known about the K(+) channels in human proximal tubule cells. Using the patch-clamp technique, we investigated the properties of an inwardly rectifying K(+) channel present in the surface membrane of cultured human proximal tubule cells of normal kidney origin. This channel was the most frequently observed K(+) channel in cell-attached patches, and cytoplasmic ATP was required to maintain channel activity in inside-out patches. Its single channel conductance was about 42 pS for inward currents and 7 pS for outward currents under the symmetrical K(+) condition. The ATP effect on channel activity was dose-dependently stimulatory within a range of 0.1 to 10 mM, and a nonhydrolyzable ATP analog, AMP-PNP (3 mM), had no effect on channel activity in either the presence or absence of ATP (1 mM). The channel activity observed in cell-attached patches was reduced to 30 to 50% of controls by a membrane-permeable nonspecific protein kinase inhibitor, K252a (1 microM), or a potent protein kinase A inhibitor, KT5720 (500 nM). In contrast, a membrane-permeable cAMP analog, 8Br-cAMP (100 microM), induced a twofold increase in channel activity. The addition of a catalytic subunit of protein kinase A (PKA-CS, 100 U/ml) to the bath in inside-out patches stimulated channel activity in the presence of 1 mM ATP. Furthermore, the channel activity maintained with 1 mM ATP in inside-out patches was suppressed by internal acidification and enhanced by alkalization. These results suggest that the activity of the inwardly rectifying K(+) channel in cultured human proximal tubule cells was ATP-dependent and regulated at least in part by cAMP/PKA-mediated phosphorylation processes and intracellular pH.
authors.affiliation: Department of Physiology II, School of Medicine, Iwate Medical University, Morioka, 020-8505, Japan. kazunaka@iwate-med.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.forename: J
authors.initials: J
authors.lastname: Hirano
authors.forename: M
authors.initials: M
authors.lastname: Kubokawa
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D046508:Culture Techniques; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*
chemical_list: D024661:Potassium Channels, Inwardly Rectifying; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases