Ca²⁺ channel actions of the non-dihydropyridine Ca²⁺ channel antagonist Ro 40-5967 in vascular muscle cells cultured from dog coronary and saphenous arteries

Summary

We studied the membrane effects of (1S,2S)-2-(2-[[3-2(benzimidazolyl) propyllmethylamino]ethyl)-6-fluoro-1,2,3,4-tetrahydro-l-isopropyl-2-naphthyl-methoxy-acetate dihydrochloride, Ro 40-5967, a new non-dihydropyridine (DHP) Ca²⁺ channel antagonist, on dog coronary and saphenous arterial vascular muscle cells using the whole-cell patch-clamp method. Long-lasting (L-type) inward currents in 20 mM Ba²⁺ were measured over a range of test potentials (300 ms) from −50 mV to + 90 mV from a holding potential of −80 mV in the presence of 1 μM Bay k8644 (a DHP Ca²⁺ agonist). Ro 40-5967 caused a concentration-dependent suppression of Ca²⁺ channel currents in muscle cells from both arteries, with greater potency on coronary than saphenous arterial cells. The concentration of Ro 40-5967 which inhibited the magnitude of peak inward currents by 50% (IC₅₀) was estimated to be 1 μM (n = 5) in muscle cells from coronary artery and 10 μM (n = 4) in saphenous artery. Ro 40-5967 (1 μM) decreased the amplitude of the activation current-voltage relationship for coronary L-type Ca²⁺ channel currents over a wider range of membrane potentials than verapamil, diltiazem, or nifedipine. In contrast, block of Ca²⁺ channel currents in saphenous artery cells by 1 μM Ro 40-5967 was only observed at command potentials positive to 0 mV. Ro 40-5967 (1 μM) significantly shifted the voltage-inactivation curve downward by 40% in coronary (n = 4), but only by 18% in saphenous arterial muscle cells (n = 3). The non-parallel shift of the coronary artery inactivation curve suggests that pronounced resting channel block is a notable feature of Ro 40-5967. The marked inhibition of Ba²⁺ current by 1 μM Ro 40-5967 in the inactivation protocol in coronary arterial muscle cells was found over the entire range of membrane holding potentials tested, while inhibition in the saphenous artery inactivation curve occurred only from holding potentials more positive than −40 mV. Therefore, Ro 40-5967 is unique: 1) in acting over a wider range of voltages, on both instantaneous and resting Ca²⁺ currents, than other Ca²⁺ antagonists; 2) in producing more significant resting state block; and 3) in acting with selectivity for coronary over saphenous arteries.