A regulated calcium channel in apical membranes of renal proximal
tubule cells.
N., Zhang Min I., and Roger G. O'neil.
Department of Integrative Biology, The University of Texas-Houston
Health Science Center, 6431 Fannin, Houston, Texas 77030, Telephone:
(713)-792-5293, FAX: (713)-794-1349, E-mail:
mzhang@girch1.med.uth.tmc.edu
APStracts 3:0186C, 1996.
Using the single channel patch clamp technique we identified a Ca++
channel in the apical membranes of rabbit cultured proximal tubule
cells. The channel is permeable to both Ca++ and Ba++ 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. While addition of forskolin (12.5 :M) was
without effect, addition of phorbol 12-myristate 13-acetate (PMA, 1
:M) activated the channel. At 0 mV pipette voltage (resting state) in
the on-cell patches, PMA increased open probability (Po) from 0 to
6.9 +2.3% (n=5) within 1-3 minutes of PMA application. Likewise,
stretching the membrane patch (-10 to -30 mm Hg) activated this
channel (Po increased to 5.3 +2.1%, n=3, at 0 mV applied pipette
potential), results consistent with a mechano-sensitive channel. The
channel displayed only modest voltage-sensitivity with mild
activation upon membrane hyperpolarization, but inactivation with
strong depolarization. The addition of the L-type Ca++ channel
blocker (antagonist), nifedipine (10 :M), completely blocked this
channel in both on-cell and inside-out patches, while the agonist,
Bay K 8644 (5 :M) was without effect. It is concluded that this
channel is a nifedipine-sensitive, PKC regulated, Ca++ channel and
that it may play a role in Ca++ signaling in the proximal tubule
cells, particularly during periods of mechanical stress.
Received 8 March 1996; accepted in final form 31 May 1996.
APS Manuscript Number C133-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96