Potentiation of sarcoplasmic reticulum Ca2+ release by 2,3-butanedione monoxime in crustacean muscle.

The effect of the chemical phosphatase 2,3-butanedione monoxime (BDM) on various aspects of excitation/contraction coupling in crustacean muscle was investigated. Despite having a depressant effect on vertebrate skeletal and cardiac muscle, BDM was a potentiator of contraction in crustacean muscle. At concentrations of 1-3 mM BDM caused an increase of potassium contractures in bundles of fibers isolated from crayfish muscle. At higher concentrations BDM caused oscillatory contractions by itself. In single voltage-clamped cut muscle fibers loaded with rhod-2, BDM (0.5-2 mM) potentiated the magnitude and duration of intracellular Ca2+ transients elicited by depolarization. At the same time BDM did not affect the rate of Ca2+ removal from the myoplasm under conditions where Ca2+ release was blocked by tetracaine. Nor did BDM increase Ca2+ entry; in fact it caused a decrease in the amplitude of the inward Ca2+ current (ICa). In microsomes isolated from lobster muscle, BDM also potentiated Ca2+ release induced by caffeine and at higher concentrations (above 3 mM) induced release by itself. At the same time it had little effect on Ca2+ uptake. These results indicate that BDM potentiates Ca2+ release in crustacean muscle possibly by dephosphorylation of the Ca(2+)-release channel.