Activation of chloride currents in murine portal vein smooth muscle cells by membrane depolarization involves intracellular calcium release.
The present study describes the first characterization of Ca(2+)-activated Cl(-) currents (I(ClCa)) in single smooth muscle cells from a murine vascular preparation (portal veins). I(ClCa) was recorded using the perforated patch version of the whole cell voltage-clamp technique and was evoked using membrane depolarization. Generation of I(ClCa) relied on Ca(2+) entry through dihydropyridine-sensitive Ca(2+) channels because I(ClCa) was abolished by 1 microM nicardipine and enhanced by raising external Ca(2+) concentration or by application of BAY K 8644. I(ClCa) was characterized by the sensitivity to Cl(-) channel blockers and the effect of altering the external anion on reversal potential. Activation of I(ClCa) after membrane depolarization was dependent on Ca(2+) release from intracellular stores. Thus the amplitude of I(ClCa) was diminished by the SR-ATPase inhibitor cyclopiazonic acid, the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenyl borate (2-APB), and the ryanodine receptor blocker tetracaine. The degree of inhibition produced by the application of 2-APB and tetracaine together was significantly greater than the effect of each agent applied alone. In current-clamp mode, injection of depolarizing current elicited a biphasic action potential, with the later depolarization being sensitive to niflumic acid (NFA; 10 microM). In isometric tension recordings, NFA inhibited spontaneous contractions. These data support a role for this conductance in portal vein excitability.
Saleh
Sohag N
SN
Department of Basic Medical Sciences, Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London, United Kingdom.
Greenwood
Iain A
IA
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D004558:Electric Stimulation; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011169:Portal Vein / Q000166:cytology / Q000502:physiology*
D002021:Buffers; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018118:Chloride Channels; D002712:Chlorides; D002118:Calcium