Manganese action potentials in mammalian cardiac muscle

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Abstract
The membrane potential in guinea-pig's papillary muscles from right ventricle was recorded by glass microelectrodes and stimulation was effected by current pulses applied through a sucrose-gap. Action potentials with overshoot were recorded in the solution lacking Na+ and Ca++ but containing 2–95 mM Mn++. The overshoot was inecease with the increased of [Mn++]o by about 30 mV/decade. Similar Mn++-dependent action potentials were also obtained in Na-free solution containing 0.6 mM Ca++. The results indicate that Mn inward current is sufficient to generate action potentials in cardiac muscle.