Voltage-dependent calcium channel current in isolated gallbladder smooth muscle cells of guinea pig.
The voltage-dependent Ca2+ current was studied in enzymatically dispersed guinea pig gallbladder smooth muscle cells using the whole cell patch-clamp technique. Depolarizing voltage (V) steps induced an inward current (I) that was carried by Ca2+. The threshold potential was -40 to -30 mV, the maximal current was observed at +10 to +20 mV, and the reversal potential was around +80 mV. I-V curves obtained with holding potentials of -80 and -40 mV were not significantly different. This current had a high sensitivity to dihydropyridine drugs, and the Ba2+ or Sr2+ current was larger than the Ca2+ current. Activation was accelerated by increasing the membrane potential. In general, the time course of decay was well fitted by the sum of two exponentials, but consideration of a third (ultra-slow) decay component was also necessary when the current generated by a 2-s command pulse was analyzed. Superimposition of activation and inactivation curves showed the presence of a significant window current. Carbachol suppressed the Ca2+ current only when the pipette contained a low concentration of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. These results show that the L-type Ca2+ current is dominant in gallbladder smooth muscle cells and may contribute to excitation-contraction coupling.
Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908.
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D000818:Animals; D001464:Barium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D005704:Gallbladder / Q000166:cytology / Q000378:metabolism*; D006168:Guinea Pigs; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008954:Models, Biological; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D013324:Strontium / Q000494:pharmacology
D015220:Calcium Channels; D004095:Dihydropyridines; D001464:Barium; D002217:Carbachol; D006493:Heparin; D013324:Strontium