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Articles in PresS, published online ahead of print December 21, 2001
J Appl Physiol, 10.1152/jap.00673.2001
Submitted on June 29, 2001
Accepted on December 18, 2001
1 Department of Human Anatomy and Physiology, University of Padova, Padova, Padova, Italy
2 Muscle Biology and Physiopathology Unit, C. N. R., Padova, Padova, Italy
* To whom correspondence should be addressed. E-mail: daniela.danieli{at}unipd.it.
Skeletal muscle type 2B fibers normally receive a moderate level of motor neuron discharge. As a consequence, we hypothesize that type 2B fiber properties should be less sensitive to the absence of the nerve. Therefore, we have investigated the response of sarcoplasmic reticulum and myofibrillar proteins of type 2B fibers isolated from rat EDL muscle after denervation (2 and 7 days). Single fibers were identified by SDS-PAGE of myosin heavy chain isoforms. Electrophysiological and isometric contractile properties of the whole muscle were also analyzed. The pCa-tension relationship of type 2B single fibers was shifted to the left at 2 days and to right at 7 days after denervation, with significant differences in the Hill coefficients and pCa threshold values in 2- versus 7-day denervated fibers. The sarcoplasmic reticulum Ca2+-uptake capacity and rate significantly decreased after 2 days of denervation, while both increased at 7 days. Caffeine sensitivity of sarcoplasmic reticulum Ca2+ release was transitory and markedly increased in 2-day-denervated fibers. Our results indicate that type 2B fibers functional properties, are highly sensitive to the interruption of nerve supply. Moreover, most of 2-day denervated changes were reverted at 7 days.
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