Mechanical restitution and recirculation fraction in cardiac myocytes and left ventricular muscle of adult rats

Abstract

Unloaded cell shortening was measured in electrically stimulated myocytes from adult rat hearts to compare the contractile response to stimulation with that in isometrically contracting left ventricular papillary muscles under similar experimental conditions, but preloaded to produce maximum twitch tension. Mechanical restitution in cells followed a biexponential function with time constants of 0.19 +/- 0.03 s and 36.4 +/- 10.2 s (7 cells from 5 hearts, n = 7/5). The time constants for papillary muscles were 0.58 +/- 0.05 s and 14.6 +/- 1.0 s (n = 6/6). In myocytes, maximum post-rest potentiation occurred after 30 to 60 s of rest. The potentiation after 60 s of rest was 2.48 +/- 0.31 times the steadystate in cells and 2.63 +/- 0.16 in papillary muscles. Recirculation fraction of C2+ as calculated from the decay of post-rest potentiation was 0.84 +/- 0.04 in single cells and 0.59 +/- 0.02 in papillary muscles (p < 0.005). Caffeine (3mM) abolished post-rest potentiation in both types of preparations. The numerical values for the time constants of mechanical restitution, potentiation factor and recirculation fraction in papillary muscles did not depend on preload. It is concluded that interval-dependent changes of contractility are preserved in single cardiac cells but the kinetics of decay of potentiation appear to have changed quantitatively.

Exponential Fitting of Postextrasystolic Potentiation May Underestimate the Cardiac Ca2+ Recirculation Fraction: A Theoretical Analysis

“…The predecessors of RF calculation and their successors have limited their use of the conventional methods to only the monotonic or exponential PESP decay [6,13,14,16,[19][20][21]. Efforts have been made to produce monotonic or exponential PESP decays by choosing beat intervals during PESP long enough so as to avoid any alternans PESP [5, 13-15, 19-21, 26-28].…”

Changes in the Rhythmoinotropic Dependence of the Myocardium in Rats with Postinfarction Cardiosclerosis after β1-Adrenoreceptor Blocking

“…Extrasystolic exposure was realized by a single extra electrical pulse 0.2, 0.225, and 0.25 sec after the beginning of the regular cycle. Exposure to periods of rest was carried out during regular contractions: electrical stimulation of the muscles was ceased for 4-60 sec (periods of rest), after which regular stimulation was renewed [7]. The results were analyzed by comparing the parameters of the postextrasystolic contraction and first contraction after a period of rest with the regular contraction.…”

“…The curves of papillary muscle isometric contractions were recorded. The functional activity of SR was evaluated by the inotropic reaction of papillary muscles to extrasystolic exposure and to periods of rest [7,13]. Extrasystolic exposure was realized by a single extra electrical pulse 0.2, 0.225, and 0.25 sec after the beginning of the regular cycle.…”

Acute effects of taurine on intracellular calcium in normal and diabetic cardiac myocytes

“…During the decay of post-rest potentiation the relationship between the amplitude of post-rest contraction n, and the immediately preceding contraction n-1, is linear, and the slope of the relationship reflects the recirculation fraction [24]. This is shown in Fig.…”

“…The fraction of Ca 2+ recirculated within the cell (recirculation fraction), was estimated as described by Ravens et al [24]. Cells were stimulated at 1.0 Hz until the Ca 2+ transient amplitude had attained a steady state.…”