Effects of manganese on 45Ca mobilization and contractile responses in rabbit aortic smooth muscle

In rabbit aortic smooth muscle, 1.5 mM Mn2+ inhibits contractile responses to norepinephrine more than those to high K+. Other associated effects include decreases in the La3+-resistant high affinity Ca2+ fraction, the high affinity Ca2+ uptake component in the Scatchard-coordinate plot, and high affinity Ca2+ uptake and binding in canine aortic microsomes. Higher (15 mM) concentrations of Mn2+ are less selective. Thus, those Ca2+ mobilization components and contractile responses associated with high affinity bound Ca2+ are more sensitive to inhibition by Mn2+.