Activation of Ca(2+)-dependent protein kinase II during repeated contractions in single muscle fibres from mouse is dependent on the frequency of sarcoplasmic reticulum Ca(2+) release.
OBJECTIVE
To investigate the importance and contribution of calmodulin-dependent protein kinase II (CaMKII) activity on sarcoplasmic reticulum (SR) Ca(2+)-release in response to different work intensities in single, intact muscle fibres.


METHODS
CaMKII activity was blocked in single muscle fibres using either the inhibitory peptide AC3-I or the pharmacological inhibitor KN-93. The effect on tetanic force production and [Ca(2+)](i) was determined during work of different intensities. The activity of CaMKII was assessed by mathematical modelling.


RESULTS
Using a standard protocol to induce fatigue (50x 70 Hz, 350 ms duration, every 2 s) the number of stimuli needed to induce fatigue was decreased from 47 +/- 3 contractions in control to 33 +/- 3 with AC3-I. KN-93 was a more potent inhibitor, decreasing the number of contractions needed to induce fatigue to 15 +/- 3. Tetanic [Ca(2+)](i) was 100 +/- 11%, 97 +/- 11% and 67 +/- 11% at the end of stimulation in control, AC3-I and KN-93 respectively. A similar inhibition was obtained using a high intensity protocol (20x 70 Hz, 200 ms duration, every 300 ms). However, using a long interval protocol (25x 70 Hz, 350 ms duration, every 5 s) no change was observed in either tetanic [Ca(2+)](i) or force when inhibiting CaMKII. A mathematical model used to investigate the activation pattern of CaMKII suggests that there is a threshold of active CaMKII that has to be surpassed in order for CaMKII to affect SR Ca(2+) release.


CONCLUSIONS
Our results show that CaMKII is crucial for maintaining proper SR Ca(2+) release and that this is regulated in a work intensity manner.
Aydin
J
J
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden. jan.aydin@ki.se
Korhonen
T
T
Tavi
P
P
Allen
D G
DG
Westerblad
H
H
Bruton
J D
JD
D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D000096926:Benzenesulfonamides
D001596:Benzylamines; D002118:Calcium; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D010455:Peptides; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C527819:AC3-I peptide; C072105:KN 93; D000096926:Benzenesulfonamides