The positive inotropic dihydropyridine Bay K 8644 does not affect calcium sensitivity or calcium release of skinned cardiac fibres.

BAY K 8644 is a positive inotropic dihydropyridine which concentration-dependently increased contractile force in guinea-pig atria at 10 to 1000 nmol/l. In chemically skinned cardiac fibres from guinea-pig hearts the substance did not change the tension induced by calcium. Also BAY K 8644 did not release calcium from intracellular myocardial stores like caffeine since it failed to evoke a contractile response in saponin-treated, calcium-loaded cardiac muscle. Thus, the drug exerts its effects neither by sensitizing the contractile apparatus to calcium nor by a caffeine-like action.