Frequency, amplitude, and propagation velocity of spontaneous Ca++-dependent contractile waves in intact adult rat cardiac muscle and isolated myocytes.

Abstract

SUMMARY. Spontaneous contractile waves due to spontaneous calcium cycling by the sarcoplasmic reticulum occur in unstimulated bulk rat papillary muscle and single rat cardiac myocytes with intact sarcolemmal function. We used video analytic techniques to quantify the wave characteristics in both bulk muscle and myocytes; laser-light scattering techniques were also employed in muscle. In muscle bathed in physiological concentrations of calcium, the true periodicity of these waves was a fraction of 1 Hz and increased up to several hertz with increases in cell calcium. This was paralleled by an increase in the frequency of scattered laser light intensity fluctuations. In myocytes, a range of spontaneous contractile wave frequencies similar to that which occurred in the muscle was observed; it could be demonstrated that an increase in superfusate calcium concentrations (2-15 mM at 23°Q increases the oscillation frequency but not amplitude. In both myocytes and muscle, low concentrations of caffeine (0.5 DIM) and higher temperature increased the oscillation frequency but diminished their amplitude. However, the scattered light fluctuations did not change with temperature and decreased with caffeine. These results demonstrate that (1) the true frequency of spontaneous sarcoplasmic reticulum oscillations in the unstimulated rat muscle and single myocytes with intact sarcolemmal function is low, i.e., a fraction of a hertz; (2) with cell calcium loading, the oscillation frequency accelerates to those frequencies measured previously in the 'calcium overload" state; (3) while scattered light fluctuations which sample myonlament motion are a sensitive, noninvasive method of detecting the oscillations in bulk muscle, they can be insensitive to the divergent changes in oscillation amplitude and frequency. (Circ Res 57: 844-855, 1985)

The Emergence of a General Theory of the Initiation and Strength of the Heartbeat

“…Factors that determine periodicity and extent of synchronization of spontaneous Ca 2+ releases: LCR's generated by "free running" SR are roughly periodic (49,54), and since they are thought to occur when luminal SR Ca 2+ reaches a threshold level (36,59,60), the period of time required for a subsequent spontaneous SR Ca 2+ release to occur following a given release is determined, in part, by the speed at which the SR becomes filled with Ca 2+ to reach the threshold level (36,37). A key principle in this regard is that like the synchronized SR Ca 2+ release triggered by an AP, the restitution time for successive spontaneous LCR's is not fixed; rather, it varies with the Ca 2+ available for SR to pump, the speed at which it pumps, and the activation status of RyR's.…”

“…There is a general misconception within the cardiac research field that a free running SR is synonymous with "Ca 2+ overload". , for example, rat and dog atria, ventricle, and Purkinje fibers and guineapig atria, Ca 2+ overload is manifested by an excessive increase in the frequency of resting LCR's (54). This perspective on the true nature of "Ca 2+ overload" is most often not understood even by "experts" within the realm of Ca 2+ dynamics, and the term "Ca 2+ overload" is often misapplied to a physiologically fast ticking SR clock, mismatched to the rate at which external AP's are delivered by the experimenter.…”

An integrated formulation of anisotropic force–calcium relations driving spatio-temporal contractions of cardiac myocytes

“…Rhythmic cardiac myocyte contractions are controlled by intracellular Ca 2+ oscillations, which are triggered by membrane depolarization under normal conditions (Kort et al 1985;Stern et al 1988;Viatchenko-Karpinski et al 1999;Vinogradova et al 2005). This depolarization induces trans-sarcolemmal Ca 2+ influx that generates synchronous Ca 2+ release from the sarcoplasmic reticulum (SR) to bring about a uniform rise in cytosolic Ca 2+ (calcium-induced calcium release (CICR) mechanism ;Fabiato 1983).…”

Nonlinear Model of Calcium Excitations in Biomembranes

“…Hence, in this case, there exists a positive feedback. We should also take into account that the considered process is non-local owing to the calcium diffusion in the outer space [4][5][6][7][8][9].…”