Effects of inhibition of sarcoplasmic reticulum calcium uptake on contraction in myocytes isolated from failing human ventricle.
OBJECTIVE
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 thapsigargin to investigate the functional contribution of this uptake system to contraction and relaxation in myocytes from failing and non-failing human ventricle.


METHODS
Myocytes were isolated from 28 failing and 18 non-failing ventricles and stimulated at 0.2 Hz, 32 degrees C in Krebs-Henseleit solution. Contraction amplitude and speed were compared before and after treatment with 1 mumol/l thapsigargin for 20 min to deplete SR Ca2+ stores.


RESULTS
Initial beat duration was longer in myocytes from failing hearts. Addition of thapsigargin significantly prolonged the beat in myocytes from 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 contraction amplitude increased at high stimulation frequencies in myocytes from non-failing hearts (from 2.6% shortening at 0.1 Hz to 4.6% at 1 Hz, P < 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 +/- 10.3% at 3 min), but not in failing (102 +/- 18%, P < 0.01 compared to non-failing at 3 min). 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.


CONCLUSIONS
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.
Davia
K
K
National Heart and Lung Institute, Imperial College, London, UK.
Davies
C H
CH
Harding
S E
SE
D000368:Aged; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D004558:Electric Stimulation; D005260:Female; D006333:Heart Failure / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology*
D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium