Long-lasting actions of Bay K 8644 on responses of guinea pig taenia coli.

1. Bay K 8644, a dihydropyridine Ca2+ agonist, (10(-6) M), induced strong rhythmic contractions in taenia coli and induced a contracture after about 5.5 hr of the application. Increases in Bay K 8644 concentrations prolonged the period of rhythmic contractions and slowed the onset of the contracture. 2. Nifedipine, a dihydropyridine Ca2+ antagonist, inhibited the delayed contracture to Bay K 8644 more than the initial rhythmic contractions. The contracture to Bay K 8644 may be preferentially dependent on extracellular Ca2+ entry in comparison with the rhythmic contractions in taenia coli.