Inactivation of calcium release from the sarcoplasmic reticulum in frog skeletal muscle.

Abstract

7. All observations could be well simulated by a two-step model for inactivation in which myoplasmic free calcium equilibrates rapidly with a high-affinity calcium Authors' names appear in alphabetical order. * Present address and address for correspondence and reprint requests. 8. An alternative model in which calcium binds to a soluble receptor (e.g. free calmodulin) and then the calcium-receptor complex binds to and directly inactivates the channel was shown to be formally identical to the preceding model. Either model could closely simulate all observations.

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

“…Because the decrease observed in Fig. 13 is qualitatively similar to that studied by Schneider and Simon (1988) and Simon et al (1991), it seems likely that it, too, was caused by Ca inactivation of Ca release, even though the A[Ca] signal had been severely attenuated by equilibration of the fiber with 20 mM EGTA.…”

“…Since the change in Ca content of the SR was ~<100 ~.M, corresponding to ~<4% of the value of [Cass], this change in slope is probably not due to SR Ca depletion. Rather, it is more likely due to Ca inactivation of Ca release (Baylor et al, 1983;Simon et al, , 1991Schneider and Simon, 1988). Unfortunately, it is difficult to tell whether a similar change in slope occurred at voltages <-63 mV because of noise in the records.…”

“…13, or 0.56, as observed in the other experiment. Schneider and Simon (1988) and Simon et al (1991) showed that the decrease observed with unmodified [Ca] transients is probably due to Ca inactivation of Ca release. Because the decrease observed in Fig.…”

“…The reason is that, after sufficient Ca has been released to saturate the myoplasmic Ca buffers, free [Ca] increases and inhibits additional release because of Ca inactivation of Ca release (Baylor et al, 1983;Simon et al, , 1991Baylor and Hollingworth, 1988;Schneider and Simon, 1988). Column 7 in Table II Table II. III, tetramethylpurpurate, and PDAA in cut fibers with only 0.1 mM EGTA in the end-pool solutions (Maylie et al, 1987a.…”

“…Under certain conditions, an increase in myoplasmic free [Ca] can acdvate the release of additional Ca from the SR, a positive feedback process known as Ca-induced Ca release (Endo, Tanaka, and Ebashi, 1968;Ford and Podolsky, 1968;Fabiato, 1984). An increase in [Ca] can also reduce the ability of the SR to release additional Ca (Baylor, Chandler, and Marshall, 1983;Simon, Schneider, and Szfics, 1985;Baylor and Hollingworth, 1988;Schneider and Simon, 1988;Simon, Klein, and Schneider, 1991). In this article, this negative feedback process is called Ca inactivation of Ca release.…”