Effect of activation of protein kinase C on excitation-contraction coupling in frog twitch muscle fibres.
Intracellular Ca2+ transients were recorded from frog twitch muscle fibres in response to voltage-clamp depolarizing pulses, using arsenazo III as an intracellular Ca2+ indicator. The effect of the activation of protein kinase C (PKC) on the Ca2+ transients was studied. With 1 microM 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 within the following 2 h. This effect of PDBu could be alleviated significantly by PKC inhibitors, 10 microM polymyxin B (PMB) or 30 microM 1-(5-isoquinolinylsulphonyl)-2-methyl-piperazine (H-7). Moreover, PDBu caused an upward shift of the strength/duration curve. In Li(+)-loaded muscle fibres the Ca2+ transients could not fully recover after 80 mM K+ exposure for 15 min, while the post-K+ Ca2- transients could be completely restored in the fibres not loaded with Li+. In the presence of 10 microM PMB or 30 microM 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+ transients in Li(+)-loaded fibres. The role of PKC in modulating excitation-contraction coupling in frog twitch muscle fibres is clearly indicated, but the mechanism(s) and physiological significance remain to be established.
Wang
X F
XF
Department of Cellular and Molecular Neurobiology, Shanghai Institute of Physiology, Chinese Academy of Sciences.
Zhu
P H
PH
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D004594:Electrophysiology; D004789:Enzyme Activation; D008094:Lithium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011898:Ranidae
D015240:Phorbol 12,13-Dibutyrate; D008094:Lithium; D011493:Protein Kinase C; D002118:Calcium