Left ventricular trabeculae from failing spontaneously hypertensive rats had significantly reduced peak stress compared to controls (8 vs 21 mN mm-2, P<=0.05) despite increased intracellular calcium.
Absolute Event Rate: 8% vs 21%
p-value: p=<=0.05
Intracellular calcium (Ca2+(i)) and isometric force were measured in left ventricular (LV) trabeculae from spontaneously hypertensive rats (SHR) with failing hearts and normotensive Wistar-Kyoto (WKY) controls. At a physiological stimulation frequency (5 Hz), and at 37 degrees C, the peak stress of SHR trabeculae was significantly (P < or = 0.05) reduced compared to WKY (8 +/- 1 mN mm(-2) (n = 8) vs. 21 +/- 5 mN mm(-2) (n = 8), respectively). No differences between strains in either the time-to-peak stress, or the time from peak to 50 % relaxation were detected. Measurements using fura-2 showed that in the SHR both the peak of the Ca2+ transient and the resting Ca2+(i) were increased compared to WKY (peak: 0.69 +/- 0.08 vs. 0.51 +/- 0.08 microM(P < or = 0.1) and resting: 0.19 +/- 0.02 vs. 0.09 +/- 0.02 microM(P < or = 0.05), SHR vs. WKY, respectively). The decay of the Ca2+ transient was prolonged in SHR, with time constants of: 0.063 +/- 0.002 vs. 0.052 +/- 0.003 s (SHR vs. WKY, respectively). Similar results were obtained at 1 Hz stimulation, and for Ca2+ (o) between 0.5 and 5 mM. The decay of the caffeine-evoked Ca2+ transient was slower in SHR (9.8 +/- 0.7 s (n = 8) vs. 7.7 +/- 0.2 s (n = 8) in WKY), but this difference was removed by use of the SL Ca2+ -ATPase inhibitor carboxyeosin. Histological examination of transverse sections showed that the fractional content of perimysial collagen was increased in SHR compared to WKY (18.0 +/- 4.6 % (n = 10) vs. 2.9 +/- 0.9 % (n = 11) SHR vs. WKY, respectively). Our results show that differences in the amplitude and the time course of the Ca2+ transient between SHR and WKY do not explain the reduced contractile performance of SHR myocardium per se. Rather, we suggest that, in this animal model of heart failure, contractile function is compromised by increased collagen, and its three-dimensional organisation, and not by reduced availability of intracellular Ca2+.
Ward et al. (Wed,) conducted a other in Heart failure. Spontaneously hypertensive rats (SHR) with failing hearts vs. Normotensive Wistar-Kyoto (WKY) controls was evaluated on Peak stress at 5 Hz and 37 degrees C (p=<=0.05). Left ventricular trabeculae from failing spontaneously hypertensive rats had significantly reduced peak stress compared to controls (8 vs 21 mN mm-2, P<=0.05) despite increased intracellular calcium.