Effects of external calcium reduction on biphasic potassium contractures and action of divalent cations on the calcium reduction in frog single twitch muscle fibers.

Abstract

The effects of external Ca2+ reduction on the biphasic potassium (K) contractures and the action of divalent cations under conditions of the Ca2+ reduction were examined in detail, using frog single twitch muscle fibers. The peak tension of the initial component of 80 mM K+ contractures was greatly potentiated by exposing the fiber to low Ca2+ solution for 30 sec, and the degree of this potentiation was decreased with increasing the exposing time. In contrast, the peak tension of the secondary component was rapidly inhibited by Ca2+ reduction. The potentiation of the initial component was removed by 3 mM Mg2+ or 0.5 mM Ni2+. The inhibition of the secondary component, especially the shortening of its time course, was reversed partially by 3 mM Mg2 + and almost completely by 0.5 mM Ni2 + . The difference between the inhibitory effect of 10 mM Mg2+ or 1-3 mM Ni2+ on the initial component and that on the secondary component was also demonstrated. The tension development of the secondary component was completely inhibited by external Ca2+ reduction for 20 min, but it was observed in the presence of 3 mM Mg2+, although its time course was shorter. These results indicate that the actions of Mg2+ and Ni2+ on the initial component differ from those on the secondary component and suggest the possible mechanisms of the actions of these divalent cations on the biphasic K contractures.Key Words: frog single twitch muscle fiber, biphasic K contractures, external Ca2+ reduction, direct effect of Cat +, Mg2+ and Ni2+ effects. LUTTGAU and SPIECKER (1979) have recently reported that by external Ca2+ reduction in the presence of Mg2+, the peak tension of the maximum contractures is slightly affected, while the time course of the contractures is shortened. STEFANI (1981, 1982) reported that under the same conditions the peak con-

Effects of divalent cations on biphasic potassium contractures and on contractile inactivation in low calcium solutions in frog single twitch muscle fibers.

“…6b). This effect of reduction in concentration of external Ca2+ is similar to that reported in our previous paper (TsUTSU-URA et al, 1984b). These changes were not observed in a solution containing Mn2+ (Fig, lc, d).…”

“…The preparation of single fibers from semitendinosus muscle of the frog (Rana japonica), the method of measurement of mechanical responses, the preparation of the solutions, and chemicals used were described previously (NAGAI et al, 1979;TAKAUJI et al, 1980TAKAUJI et al, , 1982bTsUTSU-URA et al, 1984b). Figure 1 shows the effect of Mn2 + on biphasic K contractures of a single twitch muscle fiber of a frog in a low Ca2+ solution.…”

“…The previous paper (TsUTSU-URA et al, 1984b) reported that Mg2+ and Ni2+ act on the initial component of biphasic potassium (K) contractures in a low Cat + solution differently from on their secondary component, as well as suggesting possible mechanisms of the actions of Mg2+ and Ni2+ on the biphasic K contractures from the data obtained.…”

Tension development in frog skeletal muscle induced by silver ions.

“…1 -iv in OBA and HOTTA, 1984). Since the work of FRANK (1962) appeared, it has been known that several divalent cations, including Co2+ and Nit +, could substitute for extracellular Ca2+ in the maintenance of potassium contracture with different degrees of effectiveness, in frog muscles (LoRKovIC, 1967;CAPUTO, 1981;LoRKovIc and RUDEL, 1983;TsUTSU-URA et al, 1984). Thus, we assessed the relative effectiveness of divalent cations on the maximum tension induced by 5µM Ag+.…”

Effects of conditioning depolarization, repriming, and external calcium reduction on the potassium contractures in frog single twitch muscle fibers.

“…l-9), therefore, it can be concluded that the inhibitory and potentiating changes of peak tension produced in parallel with the shortening of the time course of K contractures, which were induced by prolonged conditioning depolarization and during repriming or by reduction in external Ca2+ concentration, are generally determined by a balance between the activation and the inactivation processes of the secondary component. In our series of works concerning the biphasic K contractures (TAKAUJI et al, 1980(TAKAUJI et al, , 1982TsUTSU-URA et al, 1984), the question has been raised whether the contractile inactivation is involved in the initial component. The present result shown in Fig.…”