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

• Published in: Acta physiologica (Oxford) 2007-10, Vol.191 (2), p.131-137
• Main Authors: Aydin, J, Korhonen, T, Tavi, P, Allen, D G, Westerblad, H, Bruton, J D
• Format: Article
• Language: English
• Subjects: Animals; Benzylamines - pharmacology; Calcium - metabolism; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - antagonists & inhibitors; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - metabolism; Enzyme Activation; In Vitro Techniques; Male; Medicin och hälsovetenskap; Mice; Mice, Inbred Strains; Models, Biological; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - physiology; Peptides - pharmacology; Protein Kinase Inhibitors - pharmacology; Sarcoplasmic Reticulum - secretion; Sulfonamides - pharmacology
• ISSN: 1748-1708
• DOI: 10.1111/j.1748-1716.2007.01725.x

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. 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. 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. Our results show that CaMKII is crucial for maintaining proper SR Ca(2+) release and that this is regulated in a work intensity manner.