Effect of SCN on Potassium Contracture in Twitch Muscle Fibers of the Frog

Abstract

The

Effect of SCN on Twin Single Twitch Muscle Fibers of the Frog

“…Therefore, it seems likely that the sites of action of SCN are more deeply located structures in the fibers than the T-membrane and/or triadic junction. In our previous papers, we reported that the potentiating effect of SCN on caffeine contracture tension and the retarding effect of SCN on spontaneous relaxation of potassium contracture reached their respective maxima 10 min or more after exposure of the fibers to SCN-Ringer solution (NAGAI et al, 1978(NAGAI et al, , 1979. On the basis of these results, we considered that these effects of SCN could be caused by the direct action of SCN on sarcoplasmic reticulum (SR).…”

“…These facts do not exclude entirely the possibility that SCN acts on the T-membrane and/or triadic junction. NAGAI et al (1979) proposed the possibility that the influx and efflux of SCN are promoted by membrane depolarization. Thus, it may be considered that the rapid onset of twitch potentiation and the initial rapid phase of recovery of the potentiated twitch could be ascribed to the promotion of fluxes of SCN caused by membrane depolarization during action potential.…”

“…However, no adequate explanation of how the lengthening of the duration of negative afterpotential or mechanically effective period causes the prolongation of the duration of active state has been advanced. In previous papers, we proposed that the potentiation of potassium-and caffeine- NAGAI et al, 1978NAGAI et al, , 1979 Figure 1 is a representative result showing the effect of SCN on twitch responses in a single fiber of the frog. When a single fiber was exposed to 117.5 SCN-Ringer solution containing 117.5 mM SCN instead of an equivalent amount of Cl in normal Ringer solution, SCN potentiated the twitch tension and prolonged the duration of twitch.…”

“…Since SANDOW (1950, 1955) reported that anomalous anions such as nitrate (NO3) and thiocyanate (SCN) induced the twitch potentiation of frog skeletal muscles, many investigators have confirmed these findings and added that these anions potentiated potassium-and caffeine-contractures as well as twitch (HODGKIN and HOROWICZ, 1960;MATSUSHIMA et al, 1962;MASHIMA and MATSUMURA, 1962;SANDOW, 1965;NAGAI et al, 1978NAGAI et al, , 1979. It is generally accepted that the lengthening of the duration of negative afterpotential or mechanically effective period caused by these anions leads to a prolongation of the duration of the active state during a single twitch and then to the potentiation of twitch tension (e.g.…”