Influence of intracellular Mn on the contractile inhibition caused by db cAMP, forskolin, and porcine relaxin in the circular muscle of the estrogen-treated rat uterus.

Whether Mn ion permeates into circular muscle cells of the estrogen-treated rat uterus and how contractile inhibitions caused by db cAMP, forskolin, and relaxin are affected by treatment with Mn were examined. By exposing the muscle strip to 0.35 mM Mn added to Mg-free Krebs solution, the magnitude of phasic contractions evoked by electrical stimulation was reduced to 21.8 +/- 14.7% (n = 22) of control. Mn influx was measured by fura-2 fluorescence quenching at the Ca isosbestic excitation wavelength (360 nm). The contractile inhibitions caused by 30 microM db cAMP and 0.2 microM forskolin were enhanced after pretreatment with 0.35 mM Mn for 10 min, whereas the inhibition caused by 100 mU relaxin underwent enhancement or attenuation. These results are discussed in relation to those reported previously for the longitudinal muscle in which the influences of treatment with Mn were somewhat different.