Contractile Deactivation and Uncoupling of Crossbridges Effects of 2 , 3 - Butanedione Monoxime on Mammalian

We investigated the effects of 1 and 3 mM 2,3-butanedione monoxime (BDM, diacetyl monoxime) on excitation and contraction of cardiac muscle in several types of preparations at various levels of organization. We selected a concentration of BDM that was not expected to affect sarcolemmal calcium flux and action potential duration in cardiac tissue. Two indicators were used to record intracellular calcium. Aequorin, a bioluminescent calcium indicator, was used in studies with ferret papillary muscle preparations, and fura-2, a fluorescent calcium indicator, was used in studies with guinea pig cardiac myocytes. In both cases, addition ofBDM resulted in a reduction of peak intracellular calcium released from the sarcoplasmic reticulum and a reduction of peak twitch force. The duration of the action potential of isolated myocytes