Different inhibitions of the voltage-dependent K+ current by Ca2+ antagonists in the smooth muscle cell membrane of rabbit small intestine.
Actions of Ca2+ antagonists (verapamil, nicardipine and diltiazem) on the voltage-dependent K+ current, obtained from the fragmented smooth muscle cell membrane (smooth muscle ball; SMB) of the rabbit small intestine, were investigated using voltage clamp techniques. To eliminate the influence of the Ca2+-dependent K+ current, the voltage-dependent K+ current was recorded in 2.5 mM Mn2+ (Ca2+ omitted) solution. These three Ca2+ antagonists inhibited the peak amplitude of the K+ current, in a dose-dependent manner. During application of a long command pulse (duration, 3 s), the amplitude of the voltage-dependent K+ current decreased slowly with time. Diltiazem inhibited the K+ current with a slight prolongation of the 20% decay time, while TEA (tetraethyl-ammonium), a K+ channel blocker, inhibited the current, without affecting the decay. By contrast, verapamil and nicardipine accelerated inactivation. In the control, the voltage-dependent inactivation was also seen in the K+ current. This inactivation curve below 0 mV was not modified by 10 microM diltiazem, 5 microM verapamil nor 3 microM nicardipine. These results indicate that inhibition of the voltage-dependent K+ current by verapamil or nicardipine differed from that by diltiazem.
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology; D004553:Electric Conductivity; D007421:Intestine, Small / Q000166:cytology* / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D013757:Tetraethylammonium Compounds; D014700:Verapamil; D004110:Diltiazem; D011188:Potassium