K. Davia et al., EFFECTS OF INHIBITION OF SARCOPLASMIC-RETICULUM CALCIUM-UPTAKE ON CONTRACTION IN MYOCYTES ISOLATED FROM FAILING HUMAN VENTRICLE, Cardiovascular Research, 33(1), 1997, pp. 88-97
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 thapsigargin to investigate the functional co
ntribution of this uptake system to contraction and relaxation in myoc
ytes from failing and non-failing human ventricle. Methods: Myocytes w
ere isolated from 28 failing and 18 non-failing ventricles and stimula
ted at 0.2 Hz, 32 degrees C in Krebs-Henseleit solution. Contraction a
mplitude and speed were compared before and after treatment with 1 mu
mol/l thapsigargin for 20 min to deplete SR Ca2+ stores. Results: init
ial beat duration was longer in myocytes from failing hearts. Addition
of thapsigargin significantly prolonged the kat in myocytes from both
groups, but the increase was greater in non-failing hearts (beat dura
tion increased by 0.79+/-0.12 s in myocytes from non-failing hearts co
mpared with 0.37+/-0.12 a in those from failing, P <0.02). The contrac
tion amplitude increased at high stimulation frequencies in myocytes f
rom 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 dep
ressed relative to steady-state levels in myocytes from the non-failin
g 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-
hiring 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 funct
ion. These results are consistent with the hypothesis that the: initia
l differences had been due to decreased SR Ca2+ uptake.