Temperature affects post‐tetanic potentiation in frog skeletal muscle

Abstract

Brief tetanic contractions cause increases in twitch tension, i.e. post‐tetanic potentiation (PTP). Reducing incubation temperature produces a similar effect. The purpose of this investigation was to determine what interaction might exist between these two, powerful potentiating influences. Sartorii muscles (60‐70 mg) from male R. pipiens were dissected‐free and vertically‐mounted in water‐jacketed chambers containing oxygenated (100%), Ringer solution (pH 7.2). To determine peak twitch tension (PT, g) at different temperatures (10°‐30°C), muscles were stimulated via supramaximal square wave pulses (0.2 ms) every 10 s for 2 min before and after a 2.5 s tetanic contraction (80 Hz). Averaged PT immediately preceding tetanic stimulation was 25.2 ± 2.7, 18.1 ± 2.2 and 14.1 ± 0.9 at 10°C, 20°C and 30°C, respectively. Corresponding thermal ratios (R10) were 0.72 (10°‐20°C) and 0.78 (20°‐30°C). Peak tetanic tensions (PTT, g) and tension‐time integrals (TTI, g·s) were 47.3 ± 4.7, 60.1 ± 6.5, and 49.4 ± 5.8, and 100.9 ± 6.8, 140.4 ± 17.0 and 107.4 ±16.1 at 10°C, 20°C and 30°C, respectively. Averaged PT immediately following tetanic stimulation was 27.2 ± 2.1, 25.1 ± 0.7, and 15.4 ± 0.6 at 10°C, 20°C and 30°C, respectively. R10 values were 0.92 (10°‐20°C) and 0.61 (20°‐30°C). Results suggest that variations in temperature may affect the neural regulation of force output in poikilothermic animals.