Effects of halothane and diltiazem on L-type calcium currents in single smooth muscle cells from rabbit portal veins.
We have studied the effects of halothane and diltiazem on L-type voltage-dependent calcium currents (ICa) in single smooth muscle cells from rabbit portal veins using a whole cell voltage clamp technique. The threshold of ICa was -30mV and the peak current was reached at 0mV. Halothane (0.25, 0.5, 1.0, 1.5 and 2.0%) decreased ICa in a concentration-dependent manner and shifted the ICa activation threshold to the depolarizing side. Halothane 2.0% abolished ICa. Diltiazem 10(-8)-10(-6) mol litre-1, a calcium channel antagonist, also depressed ICa in a concentration-dependent manner. Administration of both 0.5% halothane and diltiazem 10(-7) mol litre-1 (concentrations lower than the clinical therapeutic range) abolished ICa; however, halothane did not exhibit use-dependent inhibition of ICa whereas diltiazem showed partial use-dependency. We conclude that the decrease in ICa produced by halothane is associated with a direct vasodilator effect of this anaesthetic, but is not explained by block of Ca2+ channels similar to the action of diltiazem. Furthermore, administration of low concentrations of both halothane and diltiazem decreased ICa and may reduce the contractility of the vascular smooth muscle cells.
Yamazaki
M
M
Department of Anaesthesiology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan.
Kamitani
K
K
Ito
Y
Y
Momose
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006221:Halothane / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits
D015220:Calcium Channels; D004110:Diltiazem; D002118:Calcium; D006221:Halothane