Abstract
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+KCl2.5). 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 9th and 10th pulses (ISI = 10 ms). Peak tensions (PT, g) for contractions (PTA‐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.
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