Reversible blockade of gap junctional communication by 2,3-butanedione monoxime in rat cardiac myocytes

2,3-Butanedione monoxime (BDM), a nucleophilic agent endowed with a ''phosphatase-like'' activity, is often used as a tool for investigating the effects of changes in phosphorylation level of protein constituents on membrane channel function. BDM produced a rapid, dose-dependent, and reversible abolition of the cytosolic continuity existing between cells via gap junctional channels. The persistence of this effect when a nonhydrolyzable analogue of ATP [adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S)] was introduced in the cytosol suggests that the acute suppressant effect of BDM was not due to dephosphorylation. However, the higher reversibility after BDM withdrawal in presence of ATP gamma S could signify that a protein-dephosphorylating activity gradually occurred during the oxime treatment. Junctional uncoupling took place even when the moderate increase in cytosolic Ca2+ concentration induced by BDM was prevented by ryanodine. These results are consistent with the model of dual mechanism of BDM action proposed for some other membrane channels, consisting of a quick channel block and a parallel slow inhibition, plausibly through dephosphorylation.