Xf. Wang et Ph. Zhu, EFFECT OF ACTIVATION OF PROTEIN-KINASE-C ON EXCITATION-CONTRACTION COUPLING IN FROG TWITCH MUSCLE-FIBERS, Pflugers Archiv, 428(3-4), 1994, pp. 224-231
Intracellular Ca2+ transients were recorded from frog twitch muscle fi
bres in response to voltage- clamp depolarizing pulses, using arsenate
III as an intracellular Ca2+ indicator. The effect of the activation
of protein kinase C (PKC) on the Ca2+ transients was studied. With 1 m
u M phorbol 12,13-dibutyrate (PDBu), a PKC activator, the peak of the
Ca2+ transients increased to about 120% of control during the first 0.
5 h, and then decreased gradually to a plateau of 44% of control withi
n the following 2 h. This effect of PDBu could be alleviated significa
ntly by PKC inhibitors, 10 mu M polymyxin B (PMB) or 30 mu M 1-(5-isoq
uinolinylsulphonyl)-2-methyl-piperazine (H-7). Moreover, PDBu caused a
n upward shift of the strength/duration curve. In Li+-loaded muscle fi
bres the Ca2+ transients could not fully recover after 80 mM K+ exposu
re for 15 min, while the post-K+ Ca2+ transients could be completely r
estored in the fibres not loaded with Li+. In the presence of 10 mu M
PMB or 30 mu M H-7, a full restoration of the post-K+ Ca2+ transients
was seen in Li+-loaded fibres. PMB supplemented after high-K+ exposure
also could result in a complete recovery of the post-K+ Ca2+ transien
ts in Li+-loaded fibres. The role of PKC in modulating excitation-cont
raction coupling in frog twitch muscle fibres is c clearly indicated,
but the mechanism(s) and physiological significance remain to be estab
lished.