Uptake and loss of manganese from perfused frog ventricles.

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Abstract
The uptake and loss of Mn was studied in perfused isolated frog ventricles, at rest, during activity, in Na-free fluid and in K-rich fluid. In normal Ringer the uptake of Mn with time is composed of 2 phases which can be interpreted as an initial saturating phase and a slower non-saturating phase. The uptake in the resting heart is 1.91 .times. 10-14 M .cntdot. cm-2 .cntdot. s-1, and the extra uptake associated with the action potential is 6.90 .times. 10-13 M .cntdot. cm-2 .cntdot. beat-1, when the heart is exposed to Ringer containing 8 mM-Mn. The washout of Mn from preloaded ventricles into Mn-free Ringer is composed of at least 2 exponential phases. The slowest phase corresponding to a rate of Mn efflux of 1.72 .times. 10-14 M .cntdot. cm-2 .cntdot. s-1. Mn uptake is not increased by exposure of the muscle to Na-free fluids but is markedly increased by exposure to depolarizing fluids. The Mn accumulating in the ventricles during a 7 1/2 min exposure to 8 mM-Mn-Ringer with an elevated [K], increases with increasing [K]o [outside] to reach a peak at 75 mM-K and then falls to quite a low value in 120 mM-K. The results are discussed in the light of the action of Mn2+ on the contraction and the ionic currents of frog heart muscle.