Intracellular calcium ions activate a low-conductance chloride channel in smooth-muscle cells isolated from human mesenteric artery.
Calcium-activated chloride currents were studied by the patch-clamp technique in vascular smooth muscle cells (VSMC) isolated from human mesenteric arteries. Bath application of 20 mM caffeine caused the cell membrane to depolarize by a calcium-activated inward current that peaked to -654 +/- 230 pA (holding potential -50 mV). Cell-attached, at the same time inwardly directed single-channel currents were detected with an amplitude of -0.22 pA. In open-cell-attached patches channel activity was triggered by elevating [Ca2+]i to 10 microM. At -60 mV the mean amplitude of the current was -0.24 pA and the mean open time of the channels was 28 ms. Plotting the amplitude of the current versus the test potential yielded a single-channel conductance of 2.8 +/- 0.5 pS. The currents disappeared when [Cl-] was reduced from 150 mM to 5 mM at the cytosolic side of the inside-out patch at a holding potential of -60 mV (calculated reversal potential -58 mV) suggesting that the calcium-activated current was a chloride current. This suggests that, in human mesenteric VSMC, elevation of [Ca2+]i activates a low-conductance chloride channel, which may mediate the agonist-induced depolarization of the cell membrane.
Klöckner
U
U
Department of Physiology, University of Köln, Germany.
D000200:Action Potentials / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*
D018118:Chloride Channels; D002110:Caffeine; D002118:Calcium