muscle
• in extensor digitorum longus muscle at 10 s after a tetanic stimulation (150 Hz for 2 s) no increase in twitch tension is seen, unlike in wild-type mice where a 75% increase is seen
• in extensor digitorum longus muscle following repetitive stimulation at a constant low frequency the initial transient decrease is present but during the recovery phase the maximum tension increase is only 30% compared to 55% in wild-type
• in both cases phosphorylation of regulatory light chain myosin is decreased compared to wild-type; however phosphorylation in cardiac myocytes is normal
• no other obvious abnormalities are seen in homozygous mice
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