Modification of cardiac Ca2+ release channel gating by DIDS.

The effects of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) on individual cardiac sarcoplasmic reticulum Ca2+ release channels have been examined in planar lipid bilayers. A sudden step-like increase in open probability (Po) induced by DIDS was observed. At zero holding potential it proceeded with an apparent time constant of 84 s and Po was increased 15 times in the steady state. Independent of membrane voltage, DIDS induced a long-lived open state with tau o = 15 ms at 0 mV and tau o = 5 ms at -50 mV (cis (cytoplasmic) side negative). While at 0 mV the modified channel spent most of the time in this long-lived state, at -50 mV the occupancy of the long-lived state was very low and most openings occurred to the short and medium open state, leading to deactivation of the channel to only 2-3 times of control. Voltage-induced changes in the activity of modified channels were reversible and proceeded with time constants of 14 s for deactivation and 12 s for activation, that is, faster than onset of activation by DIDS. As no changes in single channel conductance of the channel were observed in the presence of DIDS and its abrupt activating action could not be removed, a covalent modification of an amino group residing in the gating structure of the channel by DIDS can be considered.