Multiple channels mediate calcium leakage in the A7r5 smooth muscle-derived cell line.
Ca2+ entry under resting conditions may be important for contraction of vascular smooth muscle, but little is known about the mechanisms involved. Ca2+ leakage was studied in the A7r5 smooth muscle-derived cell line by patch-clamp techniques. Two channels that could mediate calcium influx at resting membrane potentials were characterized. In 110 mM Ba2+, one channel had a slope conductance of 6.0 +/- 0.6 pS and an extrapolated reversal potential of +41 +/- 13 mV (mean +/- SD, n = 8). The current rectified strongly, with no detectable outward current, even at +90 mV. Channel gating was voltage independent. A second type of channel had a linear current-voltage relationship, a slope conductance of 17.0 +/- 3.2 pS, and a reversal potential of +7 +/- 4 mV (n = 9). The open probability increased e-fold per 44 +/- 10 mV depolarization (n = 5). Both channels were also observed in 110 mM Ca2+. Noise analysis of whole-cell currents indicates that approximately 100 6-pS channels and 30 17-pS channels are open per cell. These 6-pS and 17-pS channels may contribute to resting calcium entry in vascular smooth muscle cells.
Obejero-Paz
C A
CA
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA. cao@po.cwru.edu
Jones
S W
SW
Scarpa
A
A
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000145:classification / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002460:Cell Line; D015640:Ion Channel Gating; D017136:Ion Transport; D007700:Kinetics; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats
D015220:Calcium Channels; D002413:Cations, Divalent; D002118:Calcium