Effect of angiotensin II on mechanical and electrical responses of frog, chick and rat skeletal muscle.

The effect of angiotensin II (AII) on neuromuscular transmission and muscle contraction was investigated by analyzing its effect on electrically-evoked twitch and tetanic contractions in response to motor nerve stimulation at 0.2 Hz and 20 Hz, respectively, the amplitude and duration of frog sciatic nerve compound action potential (NCAP), the uptake (and release) of 3H-methylcholine into/by the nerve-muscle preparation, and the contractures produced by depolarizing agents, e.g. acetylcholine (ACh) and tetraethylammonium (TEA) in the chick, frog and rat skeletal muscle. The results showed that AII, in low concentrations (0.1-10 nM), may facilitate neuromuscular transmission by increasing the amplitudes of indirectly-elicited twitch and tetanic contractions, by increasing the uptake of 3H-methylcholine, and by increasing the duration of the frog NCAP, by about 86%. In high concentrations (greater than 1 microM), AII had inhibitory effects on neuromuscular transmission and produced a small contracture on its own in the muscle (0.4 +/- 0.01 g of tension, n = 6).