Procaine effects on single sarcoplasmic reticulum Ca2+ release channels.

The effects of the Ca(2+)-induced Ca2+ release blocker procaine on individual sarcoplasmic reticulum Ca2+ release channels have been examined in planar lipid bilayers. Procaine did not reduce the single channel conductance nor appreciably shorten the mean open times of the channel; rather, it increased the longest closed time. These results indicated that procaine interacted selectively with a closed state of the channel rather than with an open state. Gating of the sarcoplasmic reticulum Ca2+ release channel was described by a modified scheme of Ashley and Williams (1990. J. Gen. Physiol. 95:981-1005), including an additional long-lived closed state. Computer simulations determined that procaine was more likely to interact with this long-lived Ca(2+)-bound closed state of the channel rather than with other states of the channel. Simulations with the same model were also able to reproduce a prominent Ca(2+)-sensitive transition between "random" and "bursting" forms of gating of the channel, variations of which may account for "gearshift" behavior reported in studies with this and other single channels.