AJP - Cell Physiology, Vol 271, Issue 5 C1757-C1764, Copyright © 1996 by American Physiological Society

ARTICLES

Regulated calcium channel in apical membranes renal proximal tubule cells

M. I. Zhang and R. G. O'Neil
Department of Integrative Biology, University of Texas-Houston Health Science Center 77030, USA.

Using the single-channel patch-clamp technique, we identified a Ca2+ channel in the apical membranes rabbit cultured proximal tubule cells. The channel is permeable to both Ca2+ and Ba2+ but not to monovalent cations. In on-cell patches, the channel opened infrequently and had a conductance of 4.6 +/- 0.9 pS (n = 5) with 105 mM CaCl2 in the pipette. Although addition of forskolin (12.5 microM) Cl2 is without effect, addition of phorbol 12-myristate 13-acetate (PMA, 1 microM) activated the channel. At 0 mV pipette voltage (resting state) in the on-cell patches, PMA increased open probability (P0) from 0 to 6.9 +/- 2.3% (n = 5) within 1-3 min of PMA application. Likewise, stretching the membrane patch (-10 to -30 mmHg) activated this channel (P0 increased to 5.3 +/- 2.1%, n = 3, at 0 mV applied pipette potential), with results consistent with a mechanosensitive channel. The channel displayed only modest voltage sensitivity, with mild activation on membrane hyperpolarization but with inactivation on strong depolarization. The addition of the L-type Ca2+ channel blocker (antagonist), nifedipine (10 microM), completely blocked this channel in both on-cell and inside-out patches, whereas the agonist, BAY K 8644 (5 microM) was without effect. It is concluded that this channel is a nifedipine-sensitive, protein kinase C-regulated Ca2+ channel and that it may play a role in Ca2+ signaling in the proximal tubule cells, particularly during periods of mechanical stress.

This article has been cited by other articles:

				Y. J. Lee and H. J. Han Role of ATP in DNA synthesis of renal proximal tubule cells: involvement of calcium, MAPKs, and CDKs Am J Physiol Renal Physiol, July 1, 2006; 291(1): F98 - F106. [Abstract] [Full Text] [PDF]

				J. A. T. DOW and S. A. DAVIES Integrative Physiology and Functional Genomics of Epithelial Function in a Genetic Model Organism Physiol Rev, July 1, 2003; 83(3): 687 - 729. [Abstract] [Full Text] [PDF]

				W. Wang, T.-H. Kwon, C. Li, A. Flyvbjerg, M. A. Knepper, J. Frokiar, and S. Nielsen Altered expression of renal aquaporins and Na+ transporters in rats treated with L-type calcium blocker Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2001; 280(6): R1632 - R1641. [Abstract] [Full Text] [PDF]

				M. R. MacPherson, V. P. Pollock, K. E. Broderick, L. Kean, F. C. O'Connell, J. A. T. Dow, and S. A. Davies Model Organisms: New Insights Into Ion Channel and Transporter Function.: L-type calcium channels regulate epithelial fluid transport in Drosophila melanogaster Am J Physiol Cell Physiol, February 1, 2001; 280(2): C394 - C407. [Abstract] [Full Text] [PDF]