An L-type calcium channel in renal epithelial cells.
A voltage-activated Ca++ channel has been identified in the apical membranes of cultured rabbit proximal tubule cells using the patch-clamp technique. With 105 mm CaCl2 solution in the pipette and 180 NaAsp in the bath, the channel had a conductance of 10.4 +/- 1.0 pS (n = 8) in on-cell patches, and 9.8 +/- 1.1 pS (n = 8) in inside-out patches. In both on-cell and inside-out patches, the channel is active by membrane depolarization. For this channel, the permeation to Ba++ and Ca++ is highly selective over Na+ and K+ (PCa(Ba):PNa(K) >200:1). The sensitivity to dihydropyridines is similar to that for L-type channels where the channel was blocked by nifedipine (10 microM), and activated by Bay K 8644 (5 microM). When activated by Bay K 8644, the channel showed subconductance levels. Treatment with forskolin (12.5 microM), phorbol ester (1 microM), or stretching (40 cm water) did not activate this channel. These results indicate that this Ca++ channel is mostly regulated by membrane voltage, and appears to be an epithelial class of L-type Ca++ channel. As such, it may participate in calcium reabsorption during periods of enhanced sodium reabsorption, or calcium signaling in volume regulation, where membrane depolarization occurs for prolonged periods.
Zhang
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MI
Department of Integrative Biology, The University of Texas-Houston Health Science Center, 6431 Fannin, Houston, Texas 77030, USA.
O'Neil
R G
RG
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008564:Membrane Potentials; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D012964:Sodium; D009543:Nifedipine; D011188:Potassium; D002118:Calcium