Effects of 2,3-butanedione 2-monoxime on Ca2+ release channels (ryanodine receptors) of cardiac and skeletal muscle

Single channel and [H-3]ryanodine binding measurements were performed to test for a direct functional interaction between 2,3-butanedione 2-monoxime (BDM) and the skeletal and cardiac muscle sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors). Single channel measurements were carried out in symmetric 0.25 M KCl media using the planar lipid bilayer method. BDM (1-10 mM) activated suboptimally Ca2+ activated (0.5-1 mu M free Ca2+) single, purified and native cardiac and skeletal release channels in a concentration-dependent manner by increasing the number of channel events without a change of single channel conductances. BDM activated the two channel isoforms when added to either side of the bilayer. At a maximally activating cytosolic Ca2+ concentration of 20 mu M, BDM was without effect on the cardiac channel, whereas it inhibited skeletal channel activities with IC50 approximate to 2.5 mM. In agreement with single channel measurements, high-affinity [H-3]ryanodine binding to the two channel isoforms was increased in a concentration-dependent manner at less than or equal to 1 mu M Ca2+. BDM was without a noticeable effect at low (less than or equal to 0.01 mu M) Ca2+ concentrations. At 20 mu M Ca2+, BDM inhibited the skeletal but not cardiac channel. These results suggest that BDM regulates the Ca2+ release channels from the sarcoplasmic reticulum of skeletal and cardiac muscle in a concentration, Ca2+ and tissue-dependent manner.