(S)-(-)-BAY-K-8644

EC50: 32 nM (I _Ba )

(±)-Bay K 8644, a conventional racemic mixture of Bay K 8644, is widely used as an L-type Ca ²⁺ 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 I _Ba in gastric myocytes of the guinea pig antrum. The Ca ²⁺ channel activity is enhanced by 3–30 μM (S)-(-)-Bay-K-8644 an agonist of L-type Ca ²⁺ channels. The interactions of two Ca ²⁺ channel activators (S)-(-)-Bay-K-8644 and FPL 64176 is examined on smooth muscle L-type Ca ²⁺ 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 (EC ₅₀ =14 nM). (S)-(-)-Bay-K-8644 (100 nM) increases whole-cell Ca ²⁺ currents in A7r5 smooth muscle cells but effectively blocks further stimulation by 1 μM FPL 64176.