The effect of low concentrations of sodium dodecyl-sulfate on 45Ca release in frog skeletal muscle

The release of radioactive 45Ca was studied in toe muscles of frog previously soaked in Ringer containing 0.1--0.2 mc 45Ca/ml. Sodium dodecyl-sulfate (SDS) added in concentration of 0.05 mM during the washout of the muscle in nonradioactive solution caused a moderate increase in 45Ca efflux that developed gradually to a maximum in about 30 min, then slowly declined. This increase was significantly reduced in muscles with disrupted T tubules. The transient release of 45Ca induced by EDTA (lmM) was markedly increased and prolonged by simultaneous application of the detergent. This effect had a rapid onset, a pronounced increase in 45Ca efflux being observed from the 1st min. The Ca released by the detergent was different from the self-exchangeable Ca fraction. After soaking the muscles in EDTA solution to remove superficial Ca, the addition of SDS was still able to produce a small increase in 45Ca efflux. It is concluded that SDS in low concentrations acts to reduce the binding capacity for Ca of sites located at the level of both superficial portion of the membrane and T tubular membrane. In addition, it also favours the release of Ca from sarcoplasmic reticulum sites. Thus an important effect of SDS appears to be the labilization of specific Ca sites at the level of triadic junction. This effect may account for the facilitation of excitation-contraction coupling observed with SDS in contracture studies.