Neuromuscular transmission and excitation-contraction coupling in fish red muscle.

TAKEUCHI (1959) has studied on red and white muscle fibres of fresh water fish teleost (snake fish) and observed that (1) there was no difference between the membrane potential of the red muscle and that of white one (60-70mV) , (2) the red muscle did not generate the spike but did only junction potential, (3) the white muscle generated the spike but usually did not overshoot the resting potential. Furthermore, he observed that junction potentials could be recorded from any point on the surfaces of both muscle fibres , and his results indicated that both muscles have polyaxonal innervation . Different results were observed from the sea water fish (hagfish) by ANDERSEN, JANSEN and LOYNING (1963). The membrane potential of the fast fibre was 74.6mV and that of the slow fibre was 46mV. The fast fibre gave rapid twitch contraction, while that of the slow fibre last more than 500msec . The fast muscle fibre appeared to be innervated with only one motor axon but the slow muscle fibre was usually innervated with more than two motor axons reaching the fibre. Furthermore, they reported that the red muscle could generate the spike. The different results observed from the muscles of fresh water fish and sea water fish are partly due to the phylogenitic difference. Red (fin) muscle of sea water fish, namely puffer fish, showed about 70mV of resting potential and generated overshoot potential by nerve stimulation and the spike was sodium dependent, although tetrodotoxin (10-5g/ml) had no effect on the spike generation. Furthermore, the muscle fibres were innervated multi-diffusely. (T. HIDAKA, H. KURIYAMA, T. OSA and N. TOIDA, unpublished observation). However, the red muscle in the fresh water fish, namely silver carp did not generate a spike by nerve stimulation but did an excitatory junction potential, and the membrane capacitance measured in the red muscle was much higher than that observed in the white muscle. These relations agreed nicely with those observed in the tonic and twitch fibre of frog (ADRIAN and PEACHEY 1965, HIDAKA and TOIDA 1969).