Subcontracture depolarization alters doublet potentiation

Doublet potentiation occurs when a brief, high‐frequency burst of pulses is added to a subtetanic train of pulses. The purpose of this investigation was to determine the effect of subcontracture K + ‐induced depolarization on doublet potentiation. Sartorii muscles (60‐70 mg) from R. pipiens were excised and mounted in water‐jacketed (20°C) chambers containing oxygenated (100%) Ringer's solution (R; pH 7.2) containing 2.5 mM KCl (R+KCl 2.5 ). Muscles were exposed to an 800 ms train (20 Hz) of supramaximal square‐wave pulses (.2 ms) via field stimulation. An additional pulse was inserted between the 9 th and 10 th pulses (ISI = 10 ms). Peak tensions (PT, g) for contractions (PT A‐E ) between the eighth and twelveth pulses were determined. Tension‐time integrals (TTI, g·s) were calculated. This protocol was then repeated with the [KCl] of R increased incrementally up to 15 mM/L. Subcontracture depolarization lessens the effect of transient high‐frequency paired stimulation and may mitigate its potential as a motor control strategy.