title: Non-steady-state calcium handling in failing hearts from the spontaneously hypertensive rat.
abstract: It is generally agreed that changes in Ca(2+) cycling are often associated with heart failure, yet the impact of these changes on a beat-to-beat basis remains unclear. Measurements of isometric force and [Ca(2+)](i) were made at 37°C in left ventricular trabeculae from failing spontaneously hypertensive rat (SHR) hearts, and their normotensive Wistar-Kyoto (WKY) controls. At 1 Hz, peak stress was reduced in SHR (14.5 ± 2.4 mN mm(-2) versus 22.5 ± 6.7 mN mm⁻² for WKY), although the Ca(2+) transients were bigger (peak [Ca(2+)](i) 0.60 ± 0.08 μM versus 0.38 ± 0.03 μM for WKY) with a slower decay of fluorescence (time constant 0.105 ± 0.005 s versus 0.093 ± 0.002 s for WKY). To probe dynamic Ca(2+) cycling, two experimental protocols were used to potentiate force: (1) an interval of 30 s rest, and (2) a 30-s train of paired-pulses, and the recirculation fraction (RF) calculated for recovery to steady-state. No difference was found between rat strains for RF calculated from either peak force or Ca(2+), although the RF was dependent on potentiation protocol. Since SR uptake is slower in SHR, the lack of change in RF must be due to a parallel decrease in trans-sarcolemmal Ca(2+) extrusion. This view was supported by a slower decay of caffeine-induced Ca(2+) transients in SHR trabeculae. Confocal analysis of LV free wall showed t-tubules were distorted in SHR myocytes, with reduced intensity of NCX and SERCA2a labelling in comparison to WKY.
authors.affiliation: Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland 1023, New Zealand. m.ward@auckland.ac.nz
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Ward
authors.forename: David J
authors.initials: DJ
authors.lastname: Crossman
authors.forename: Denis S
authors.initials: DS
authors.lastname: Loiselle
authors.forename: Mark B
authors.initials: MB
authors.lastname: Cannell
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006333:Heart Failure / Q000473:pathology / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D066298:In Vitro Techniques; D009200:Myocardial Contraction; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012508:Sarcolemma / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: C506948:Atp2a2 protein, rat; D019831:Sodium-Calcium Exchanger; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium