Some effects of the calcium promotor BAY K 8644 on feline cerebral arteries

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Abstract
The proposed Ca promotor BAY K 8644 [methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate] contracted feline basilar arteries partially depolarized by 10 mmol .cntdot. l-1 K in a concentration-dependent manner (EC50 [drug concentration for half-maximum response] value: (2.1 .+-. 1.2) .times. 10-9 mol .cntdot. l-1). The concentration-responses curve for prostaglandin (PG) F2.alpha. was displaced to the left after pretreatment with BAY K 8644. PGF2.alpha. induced a biphasic contraction in Ca-free medium as was described previously. The 2nd PGF2.alpha.-induced contraction phase in Ca-free medium was abolished by pretreatment with nifedipine or diltiazem. BAY K 8644 restored the 2nd phase in arteries pretreated with nifedipine, but not in vessels pretreated with diltiazem. BAY K 8644 may act as a promotor of Ca-influx, probably by interaction with the dihydropyridine receptor in the cell membrane, and also provide support for the view that PGF2.alpha. releases membrane-bound Ca.