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Research Article Free access | 10.1172/JCI116890

Patch-clamp evidence for calcium channels in apical membranes of rabbit kidney connecting tubules.

S Tan and K Lau

Department of Medicine, University of Oklahoma, Oklahoma City.

Find articles by Tan, S. in: PubMed | Google Scholar

Department of Medicine, University of Oklahoma, Oklahoma City.

Find articles by Lau, K. in: PubMed | Google Scholar

Published December 1, 1993 - More info

Published in Volume 92, Issue 6 on December 1, 1993
J Clin Invest. 1993;92(6):2731–2736. https://doi.org/10.1172/JCI116890.
© 1993 The American Society for Clinical Investigation
Published December 1, 1993 - Version history
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Abstract

To test the hypothesis that Ca channel plays a role in renal epithelial Ca transport, we exposed and patched apical membranes of freshly microdissected rabbit connecting tubules (CNTs). Single channel Ca currents were recorded with Ba as the charge carrier. In the cell-attached mode, 8-Br-cAMP increased the open-state probability (Po) to 0.6%. In excised, inside-out patches, Po was low spontaneously and remained low during either bath protein kinase A catalytic subunit (PKAcs) or Bay K 8644. Exposure to both agonists, however, unmasked Ca channels previously latent with only one, raising Po by 1.05% at membrane potential of -70 mV. Mean Po for 14 seals (2.57%) peaked at -70 mV, declining with either hyperpolarization or depolarization. The slope conductance was 25 pS. The extrapolated reversal potential (138 mV) agrees with the calculated equilibrium potential for Ca (158 mV). The Ca to Na permeability ratio exceeded 2,800. In four patches stimulated by Bay K 8644 and PKAcs, bath nifedipine reduced Po from 1.03 to 0.15% at -63 mV. These patch-clamp data demonstrate a selective, 25-pS, cAMP/PKAcs-sensitive Ca channel in apical membranes of CNT. Po is stimulated by PKAcs and dihydropyridine (DHP) agonist, but inhibited by DHP antagonist and by depolarization. The data are consistent with the potential role of apical membrane Ca channel in epithelial Ca transport.

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