Reduced contraction strength with increased intracellular [Ca2+] in left ventricular trabeculae from failing rat hearts.
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
Marie-Louise
ML
Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. m.ward@auckland.ac.nz
Pope
Adèle J
AJ
Loiselle
Denis S
DS
Cannell
Mark B
MB
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002303:Cardiac Output, Low / Q000503:physiopathology*; D003094:Collagen / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006352:Heart Ventricles; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012508:Sarcolemma / Q000378:metabolism; D014018:Tissue Distribution
D003094:Collagen; D002118:Calcium