title: Nisoldipine-induced relaxation in intact and skinned smooth muscles of rabbit coronary arteries.
abstract: In smooth muscles of the rabbit coronary artery, nisoldipine inhibited the phasic and tonic responses of the contraction induced by 128 mM K (the IC50 values were 4 X 10(-8) M and 1 X 10(-13) M, respectively). This agent also inhibited the tonic response of the acetylcholine (ACh) (10(-5) M)-induced contraction (the IC50 value was 3 X 10(-10) M), but only slightly inhibited the phasic response (in 10(-7) M, 0.86 times the control). Nisoldipine (less than 10(-7) M) had no effect on the K-induced depolarization of the membrane at any given concentration. This drug (5 X 10(-8) M) did inhibit the oscillatory potential changes and spike potential evoked on the ACh-induced slow depolarization. After depletion of stored Ca from the polarized muscles (5.9 mM K), muscle cells accumulated Ca by application of 2.6 mM Ca without generation of contraction, i.e. a subsequently applied 20 mM caffeine produced the contraction in Ca-free solution. Nisoldipine (less than 10(-7) M) had little effect on this accumulation of Ca. The rate of rise and time to reach the maximum amplitude of the 128 mM K- or ACh-induced contraction (in 2.6 mM Ca) depended on the amount of stored Ca in cells. Nisoldipine (10(-8) M) consistently inhibited the Ca-induced contraction evoked in depolarized muscles (128 mM K), regardless of the amount of stored Ca. However, this agent (10(-8) M) did not inhibit the Ca release from storage sites evoked by activation of the muscarinic receptor. After prolonged superfusion (over 120 min) with Na- and Ca-free solution (guanethidine and atropine were present), application of 2.6 mM Ca produced contraction which was inhibited by 10(-8) M nisoldipine, while the depolarization induced by application of these solutions was not inhibited by nisoldipine. In saponin-skinned muscles, nisoldipine had no effect on the contractile proteins, as estimated from the pCa-tension relationship, or on the Ca accumulation into the Ca release from the Ca storage sites, as estimated from the caffeine-induced contraction. It is concluded that nisoldipine possesses a selective inhibitory action on voltage-dependent Ca influx, when the Ca channel is activated by depolarization.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003285:Contractile Proteins / Q000378:metabolism; D003331:Coronary Vessels / Q000187:drug effects*; D004347:Drug Interactions; D004594:Electrophysiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015737:Nisoldipine; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D013779:Tetrodotoxin / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D003285:Contractile Proteins; D014665:Vasodilator Agents; D002110:Caffeine; D013779:Tetrodotoxin; D015737:Nisoldipine; D009543:Nifedipine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium