Sensitivity of cultured and skinned chick myotube to calcium, strontium, and barium ions examined by recording isometric contractions

Abstract

Sensitivity of cultured chick myotubes to alkaline earth metal ions was investigated by recording contractile isometric tension through a semiconductor transducer. The myotubes were obtained by culturing myoblasts of chick embryo breast muscles, and skinned chemically before physiological experiments. Contractions developed in response to Ca2+ in a bathing medium higher than 3 x 10(-7) M and reached maximum at 1 x 10(-5) M. Sr2+ was less effective than Ca2+; the threshold concentration was 1 x 10(-5) M and the tension reached maximum at 1 x 10(-3) M. Ba2+ was the least effective among the three alkaline earth metal ions; only one fifth of the Ca(2+)-induced maximum tension was attained at 1 x 10(-3) M. The sensitivity was similar to that of the mature pectoral muscle fiber, a fast twitch muscle fiber, rather than that of the anterior latissimus dorsi, a slow tonic muscle fiber. The sensitivity was shown to be dependent on its troponin C by replacing it with troponin C from the mature pectoral or cardiac muscle. This indicates that TnC of a fast-muscle type is expressed in the cultured chick myotube as in the mature pectoral muscle. The contractile apparatus was thus shown to be well developed in the cultured myotube with characteristics similar to the mature fast twitch muscle fiber.

Dynamic laser light scattering studies of the effects of pyrophosphate on cyclic motions of cross-bridges in isolated thick myofilaments fromLimulus striated muscle

“…Activation of the contractile apparatus of striated muscle by Ba 2 + and Sr 2+has been studied to obtain more information about the mechanism of force generation22. 23. In isolated thick myofilaments from Limulus striated muscle, the effect of Sr 2+ had been tested by substituting the Ca 2+ in the activating solution by an equimolar concentration of Sr 2+ or Ba 2+ ( fig.…”