V. Bonnet et al., POTENTIATION OF THE TWITCH RESPONSES BY INHIBITORS OF SARCOPLASMIC-RETICULUM CA2-ATPASE IN FROG ATRIAL FIBERS(), European journal of pharmacology, 264(1), 1994, pp. 69-76
In frog atrial fibres, cyclopiazonic acid as well as thapsigargin, whi
ch are inhibitors of sarcoplasmic reticulum Ca2+-ATPase, induced a sig
nificant increase in the twitch amplitude without detectable changes i
n its kinetics. The measurements performed on chemically skinned fibre
s show that cyclopiazonic acid has no effect on the properties of cont
ractile proteins. In the presence of a T-type Ca2+ channel blocker or
L-type Ca2+ channel blocker, cyclopiazonic acid still induced a potent
iation of the twitch while no effect was found in the presence of a Na
+-Ca2+ exchange blocker. The effect of cyclopiazonic acid was not rela
ted to any modification in myofibrillar Ca2+ sensitivity or in Ca2+ in
flux through Ca2+ channels. It is proposed that the inhibition of the
sarcoplasmic reticulum Ca2+-ATPase resulted in a potentiation of the e
ffect of the Ca2+ influx and that the major role of the sarcoplasmic r
eticulum was to limit the intracellular Ca2+ concentration.