Uptake and loss of manganese from perfused frog ventricles

Abstract

1. The uptake and loss of Mn has been studied in perfused isolated frog ventricles, at rest, during activity, in Na-free fluid and in K-rich fluid. 2. In normal Ringer the uptake of Mn with time is composed of two phases which can be interpreted as an initial saturating phase and a slower non-saturating phase. The uptake in the resting heart is estimated to be 1.91 X 10(-14) M.cm-2.sec-1, and the extra uptake associated with the action potential to be 6.90 X 10(-13) M.cm-2.beat-1, when the heart is exposed to Ringer containing 8 mM-Mn. 3. The washout of Mn from preloaded ventricles into Mn-free Ringer is composed of at least two exponential phases. The slowest phase corresponding to a rate of Mn efflux of 1.72 X 10(-14) M.cm-2.sec-1. 4. Mn uptake is not increased by exposure of the muscle to Na-free fluids but is markedly increased by exposure to depolarizing fluids. 5. 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 to reach a peak at 75 mM-K and then falls to quite a low value in 120 mM-K. 6. The results are discussed in the light of the action of Mn ions on the contraction and the ionic currents of frog heart muscle.