Modulation of the calcium release channel of sarcoplasmic reticulum by adriamycin and other drugs

Abstract

The calcium release channel of sarcoplasmic reticulum mediates Ca 2+ release which triggers muscle contraction in excitation-contraction coupling. The channels have been identified morphologically with the feet structures, which are involved in junctional association of terminal cisternae of sarcoplasmic reticulum with the transverse tubules to form the triad junction. In this study, we further characterize the action of drugs on the calcium release channel from sarcoplasmic reticulum fused into planar bilayers. Adriamycin is an effective cancer chemotherapeutic drug, which is limited by its cardiotoxicity. The drug, when added to the myoplasmic side ( cis side), activates channel opening at μM concentrations in a dose dependent manner. Adriamycin together with ATP (mM) gives optimal activation, with an open probability ( P 0) of ≈1.0. Ruthenlum red added to the cis side, equivalent to the cytoplasmic (myoplasmic) domain, completely blocks channel opening. Qualitatively similar results are obtained with adriamycinol, the major metabollte of adriamycin. The inhibition by adriamycin is not reversed by reperfusion to wash out the drug. Silver ions are also found to activate the channel. The conductance of the channel activated by adriamycin, adriamycinol or Ag + is ≈100 ps, similar to that previously reported for activation of the channel with Ca 2+ and ATP. Ruthenium red has previously been observed to block channel activation from the cytoplasmic side. We now find that ruthenium red is also effective in blocking channel activity when added to the luminal ( trans) side. The block from the luminal side is different in that: (1) subconductance levels can prominantly be observed; and (2) the block of ryanodine activation is complete.