(S)-(-)-Bay-K-8644 is an agonist of L-type Ca2+ channel. (S)-(-)-Bay-K-8644 activates Ba2+ currents (IBa) (EC50=32 nM).IC50 & Target: EC50: 32 nM (IBa)In Vitro: (±)-Bay K 8644, a conventional racemic mixture of Bay K 8644, is widely used as an L-type Ca2+ channel agonist. Each optical isomer possesses opposite effects on IBa (R(+)-Bay K 8644 as an antagonist and (S)-(-)-Bay-K-8644 as an agonist. (S)-(-)-Bay-K-8644 can prevent the inhibitory actions of two distinct cyclic nucleotide pathways on IBa in gastric myocytes of the guinea pig antrum. The Ca2+ channel activity is enhanced by 3–30 μM (S)-(-)-Bay-K-8644 an agonist of L-type Ca2+ channels[2]. The interactions of two Ca2+ channel activators (S)-(-)-Bay-K-8644 and FPL 64176 is examined on smooth muscle L-type Ca2+ channels. FPL 64176 (300 nM) causes a sustained contraction of rat tail artery strips. This contractile response is inhibited by approximately 70% by (S)-(-)-Bay-K-8644 (EC50=14 nM). (S)-(-)-Bay-K-8644 (100 nM) increases whole-cell Ca2+ currents in A7r5 smooth muscle cells but effectively blocks further stimulation by 1 μM FPL 64176.