MODAL GATING IN NEURONAL AND SKELETAL-MUSCLE RYANODINE-SENSITIVE CA2+RELEASE CHANNELS

The bursting behavior of ryanodine-sensitive single Ca2+ release chann els present in chicken cerebellum endoplasmic reticulum (ER), rat hipp ocampus ER, and frog and rabbit skeletal muscle sarcoplasmic reticulum was established. Unconditional dwell time distributions fitted by the maximum likelihood method reveal at least three open and closed expon ential components. Trains of low open probability (P-0,) bursts were i nterspersed with trains of high P-0 bursts (greater than or equal to 0 .8) in all the ryanodine receptor isotypes tested. The gating kinetics of the Ca2+ release channels were defined in long recordings by analy zing burst sequences and gamma distributions of average intraburst ope n (T-0) and closed times (T-c). The gamma distributions of T-0 had two gamma components, suggesting the existence of two distinct burst type s. In contrast, the gamma distributions of T-c had only one component. The correlation between consecutive burst pairs was defined in terms of T-0 and then statistically tested by 2 x 2 matrix contingency analy sis. The probability that the ubiquitous sequential burst pattern was generated by random occurrence was <0.01 (two-tailed Fisher's exact te st). Temporal correlations were observed in all ryanodine receptor iso types under a variety of experimental conditions. These data strongly suggest that single Ca2+ release channels switch slowly between modes of gating. We propose that the effects of agonists of Ca2+ release cha nnels such as Ca2+ itself can be explained as concentration-dependent changes in the availability of each mode.