Calmodulin kinase modulates Ca2+ release in mouse skeletal muscle.
Activation of the contractile machinery in skeletal muscle is initiated by the action-potential-induced release of Ca2+ from the sarcoplasmic reticulum (SR). Several proteins involved in SR Ca2+ release are affected by calmodulin kinase II (CaMKII)-induced phosphorylation in vitro, but the effect in the intact cell remains uncertain and is the focus of the present study. CaMKII inhibitory peptide or inactive control peptide was injected into single isolated fast-twitch fibres of mouse flexor digitorum brevis muscles, and the effect on free myoplasmic [Ca2+] ([Ca2+]i) and force during different patterns of stimulation was measured. Injection of the inactive control peptide had no effect on any of the parameters measured. Conversely, injection of CaMKII inhibitory peptide decreased tetanic [Ca2+]i by ~25 %, but had no significant effect on the rate of SR Ca2+ uptake or the force-[Ca2+]i relationship. Repeated tetanic stimulation resulted in increased tetanic [Ca2+]i, and this increase was smaller after CaMKII inhibition. In conclusion, CaMKII-induced phosphorylation facilitates SR Ca2+ release in the basal state and during repeated contractions, providing a positive feedback between [Ca2+]i and SR Ca2+ release.
Tavi
Pasi
P
Department of Physiology and Pharmacology, Karolinska Institutet, 171 77 Stockholm, Sweden.
Allen
David G
DG
Niemelä
Perttu
P
Vuolteenaho
Olli
O
Weckström
Matti
M
Westerblad
Håkan
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology; D004558:Electric Stimulation; D004789:Enzyme Activation / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D009994:Osmolar Concentration; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
C114422:CAMK2N2 protein, human; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000252:Calcium-Transporting ATPases; D002118:Calcium