Spontaneous sarcoplasmic reticulum calcium release in @entity35 and XXXX cardiac muscle: relation to transient and rested-state twitch @entity2701 .

@entity35 @entity8452 @entity95 @entity5834 @entity2701 @entity9756 @entity141 @entity3917
@entity3917 ( @entity3917 ) (which monitor spontaneous @entity141 release from the sarcoplasmic reticulum [SR]) and resting and twitch @entity2701 were measured during intervals after stimulation in @entity35 and @entity95 papillary muscles. For 1 to 5 seconds after stimulation of @entity35 muscle bathed in 1.5 mM [ @entity141 ] (Cao), twitch and resting @entity2701 are depressed and @entity3917 are transiently abolished. @entity3917 and resting @entity2701 then recover simultaneously and monotonically but lag behind the restitution of twitch @entity2701 . In the absence of further stimulation, @entity3917 persist and the rested state twitch amplitude remains potentiated. When Cao is increased above 2.5 mM, the restitution of all parameters following stimulation is accelerated and becomes oscillatory; the lag of @entity3917 and resting @entity2701 restitution behind that of the twitch increases such that twitch amplitude increases, overshoots, and decreases to a nadir as @entity3917 and resting @entity2701 reach their initial maximum. In a given muscle, the maximum twitch amplitude occurs at approximately the same level of @entity3917 ; when this level is exceeded, either transiently during monotonic or oscillatory recovery after stimulation in a given Cao or in the steady rested state by an increase in Cao, twitch @entity2701 decreases. @entity8452 (1 microM), @entity5834 (10 mM), or replacement of Cao with @entity9756 abolishes @entity3917 and causes twitch amplitude to decay with rest. In contrast to @entity35 , twitch amplitude in @entity95 muscle bathed in physiological Cao decays with rest and @entity3917 are nonmeasurable at any interval following stimulation. When Cao is increased to 20 mM during rest, @entity3917 occur and the rest decay of the twitch is abolished. We interpret the parallel behavior of @entity3917 and rest potentiation to indicate that in the presence of @entity3917 , the average SR @entity141 load within the tissue is high. Depolarization of a tissue exhibiting @entity3917 causes a large twitch but also a transient depletion of the average SR @entity141 load. That the restitution of @entity3917 lags behind recovery of twitch amplitude suggests that the onset of spontaneous SR @entity141 release requires a delay following SR @entity141 replenishment. The simultaneous occurrence of spontaneous @entity141 release in a sufficient number of cells places an upper limit on twitch amplitude either during recovery following stimulation or at rest.
