Actions of Mn2+ in the presence of ionophore A23187 in taenia coli of guinea-pig

In this work, we have investigated whether Mn2+ enters the cytoplasm in the presence of ionophore for divalent cations? A23187 and induces contraction of taenia coli. In Ca2+-free, 60 mM K+ medium, the application of 5 mM Mn2 + evoked contraction and a concomitant increase in Mn2+ influx into the cyt oplasm. However, in Ca2+-free medium, the application of 5 mM Mn2+ in the p resence of 1 x 10(-5) M A23187 did not evoke both contraction and Mn2+ infl ux. These results suggest that Mn2+ penetrates through Ca2+ channels in a s tate of membrane depolarization with K+ and activates the contractile prote ins in taenia coli. However, Mn2+ does not enter the cytoplasm in the prese nce of ionophore A23187 and then does not induce contraction. (C) 2000 Acad emic Press.