Zhang M I, O'Neil R G
Department of Integrative Biology, The University of Texas-Houston Health Science Center, 6431 Fannin, Houston, Texas 77030, USA.
J Membr Biol. 1996 Dec;154(3):259-66. doi: 10.1007/s002329900150.
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.
运用膜片钳技术，在培养的兔近端小管细胞顶端膜中鉴定出一种电压激活的Ca++通道。当移液管内溶液为105 mM CaCl2且浴槽内溶液为180 mM NaAsp时，该通道在细胞贴附式膜片中的电导为10.4±1.0 pS（n = 8），在外翻式膜片中的电导为9.8±1.1 pS（n = 8）。在细胞贴附式和外翻式膜片中，该通道均通过膜去极化激活。对于此通道，Ba++和Ca++的通透对Na+和K+具有高度选择性（PCa(Ba):PNa(K)>200:1）。其对二氢吡啶的敏感性与L型通道相似，该通道可被硝苯地平（10 μM）阻断，被Bay K 8644（5 μM）激活。当被Bay K 8644激活时，该通道呈现亚电导水平。用福司可林（12.5 μM）、佛波酯（1 μM）处理或拉伸（40 cm水柱）均不能激活此通道。这些结果表明，该Ca++通道主要受膜电压调节，似乎是上皮类L型Ca++通道。因此，它可能在钠重吸收增强期间参与钙重吸收，或在容量调节中的钙信号传导过程中发挥作用，此时膜去极化会持续较长时间。
