Effects of inhibition of sarcoplasmic reticulum calcium uptake on contraction in myocytes isolated from failing human ventricle

Abstract

Objectives: There has been debate regarding the level of sarcoplasmic reticulum (SR) Ca2+ATPase protein in heart failure. We have used the SR Ca2+ATPase inhibitor thapsigarginto investigatethe functionalcontributionof this uptake system to contractionand relaxation in myocytes from failing and non-failinghuman ventricle. Methods: Myocytes were isolated from 28 failing and 18 non-failingventriclesand stimulatedat 0.2 Hz, 32°Cin Krebs-Henseleit solution.Contractionamplitudeand speed were compared before and after treatment with 1 Kmol/1 thapsigargin for 20 min to deplete SR Ca2+ stores. Results: Initial beat duration was longer in myocytesfrom failing hearts. Additionof thapsigarginsignificantlyprolongedthe beat in myocytesfrom both groups,but the increase was greater in non-failing hearts (beat duration increased by 0.79+ 0.12 s in myocytes from non-failing hearts compared with 0.37+ 0.12 s in those from failing, P < 0.02). The contractionamplitudeincreasedat high stimulationfrequenciesin myocytesfrom non-failinghearts(from2.6?Z0shortening at 0.1 Hz to 4.6% at 1 Hz, F'<0.001, n = 9), but not in those from failing hearts (1.8% at 0.1 Hz compared with 1.7% at 1 Hz, n = 5). Thapsigargin abolished the positive staircase in the non-failing, but had no effect in the failing group. Contraction amplitude following a rest interval was significantly depressed relative to steady-state levels in myocytes from the non-failing hearts (44.8~10.39'oat 3 rein), but not in failing (102 f 18%, F'<0.01 compared to non-failing at 3 rein). Following thapsigargin treatment, there were no longer significant differences between failing and non-failing myocytes in the time course of the beat, frequency response or post-rest behaviour. Conclusion: The differences between myocytes from failing and non-failing hearts were reduced by inhibition of SR function. These results are consistent with the hypothesis that the initial differences had been due to decreased SR Ca2+ uptake.

Oxidized LDL induces ventricular myocyte damage and abnormal electrical activity?role of lipid hydroperoxides

“…This data suggest a slowing of Ca 2+ -removal from the cytoplasm, whereby an impairment of the sarcoplasmic reticulum calcium ATPase (SERCA) [29], as reported for oxidative stress [31], is the most likely explanation. Such a SERCA impairment would subsequently lead to a decrease of calcium release which may account for the slowing in contraction onset, whereas a possible dysfunction of Ca 2+ release [28] may also play a role.…”

Ca2+ signalling in cardiovascular disease: the role of the plasma membrane calcium pumps

“…Cardiac excitation-contraction (E-C) coupling involves a tightly regulated sequential series of events which results in the cyclical increase in free intracellular [4][5][6], and numerous genes involved in calcium homeostasis have been reported to be altered in heart failure. For example, many studies show the downregulation of SERCA in both animal models [7] and human tissue samples from failing heart [8]. Borlak and Thum [9] have shown that in human end stage heart failure, left ventricular expression of PMCA1, PMCA4, and SERCA2 is reduced to 30%, 50%, and 30%, respectively, compared with the controls.…”

Sarcoplasmic reticulum Ca2+-ATPase overexpression by adenovirus mediated gene transfer and in transgenic mice

“…Again, observations were subject to controversy; some indicating depressed SERCA2a protein w x w x levels 7,14 and others showing no changes 8,9,15 . Additionally, some alternative functional approaches to investigate SERCA2a involvement in altered contractile function have shown that the calcium sequestering function of the sarcoplasmic reticulum is affected in human w x heart failure 8,11,12,[16][17][18][19][20][21] . A chronological summary of the findings related to alterations of SERCA2a in human heart failure is given in Table 1.…”