A novel antagonist, No. 7943, of the Na+/Ca2+ exchange current in guinea-pig cardiac ventricular cells.
1. The effects of No. 7943 on the Na+/Ca2+ exchange current and on other membrane currents were investigated in single cardiac ventricular cells of guinea-pig with the whole-cell voltage-clamp technique. 2. No. 7943 at 0.1-10 microM suppressed the outward Na+/Ca2+ exchange current in a concentration-dependent manner. The suppression was reversible and the IC50 value was approximately 0.32 microM. 3. No. 7943 at 5-50 microM suppressed also the inward Na+/Ca2+ exchange current in a concentration-dependent manner but with a higher IC50 value of approximately 17 microM. 4. In a concentration-response curve, No. 7943 raised the K(m)Ca2+ value, but did not affect the Imax value, indicating that No. 7943 is a competitive antagonist with external Ca2+ for the outward Na+/ Ca2+ exchange current. 5. The voltage-gated Na+ current, Ca2+ current and the inward rectifier K+ current were also inhibited by No. 7943 with IC50S of approximately 14, 8 and 7 microM, respectively. 6. In contrast to No. 7943, 3', 4'-dichlorobenzamil (DCB) at 3-30 microM suppressed the inward Na+/Ca2+ exchange current with IC50 of 17 microM, but did not affect the outward exchange current at these concentrations. 7. We conclude that No. 7943 inhibits the outward Na+/Ca2+ exchange current more potently than any other currents as a competitive inhibitor with external Ca2+. This effect is in contrast to DCB which preferentially inhibits the inward rather than the outward Na+/Ca2+ exchange current.
Watano
T
T
Department of Biology, Kanebo Co. Ltd., Osaka, Japan.
Kimura
J
J
Morita
T
T
Nakanishi
H
H
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D004594:Electrophysiology; D006168:Guinea Pigs; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D015220:Calcium Channels; D002413:Cations, Divalent; D015222:Sodium Channels; D013890:Thiourea