What Limits the Velocity of Fast-skeletal Muscle Contraction in Mammals?

Nyitrai, Miklos and Rossi, Rosetta and Adamek, Nancy and Pellegrino, Maria Antonietta and Bottinelli, Roberto and Geeves, Michael A. (2006) What Limits the Velocity of Fast-skeletal Muscle Contraction in Mammals? Journal of Molecular Biology, 355 (3). pp. 432-42. ISSN 00222836. (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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In rat skeletal muscle the unloaded shortening velocity (V(o)) is defined by the myosin isoform expressed in the muscle fibre. In 2001 we suggested that ADP release from actomyosin in solution (controlled by k(-AD)) was of the right size to limit V(o). However, to compare mechanical and solution kinetic data required a series of corrections to compensate for the differences in experimental conditions (0.5M KCl, 22 degrees C for kinetic assays of myosin, 200mM ionic strength, 12 degrees C to measure V(o)). Here, a method was developed to prepare heavy meromyosin (HMM) from pure myosin isoforms isolated from single muscle fibres and to study k(-AD) (determined from the affinity of the acto-myosin complex for ADP, K(AD)) and the rate of ATP-induced acto-HMM dissociation (controlled by K(1)k(+2)) under the same experimental condition used to measure V(o). In fast-muscle myosin isolated from a wide range of mammalian muscles, k(-AD) was found to be too fast to limit V(o), whereas K(1)k(+2) was of the right magnitude for ATP-induced dissociation of the cross-bridge to limit shortening velocity. The result was unexpected and prompted further experiments using the stopped-flow approach on myosin subfragment-1 (S1) and HMM obtained from bulk preparations of rabbit and rat muscle. These confirmed that the rate of cross-bridge dissociation by ATP limits the velocity of contraction for fast myosin II isoforms at 12 degrees C, while k(-AD) limits the velocity of slow myosin II isoforms. Extrapolating our data to 37 degrees C suggests that at physiological temperature the rate of ADP dissociation may limit V(o) for both isoforms.

Item Type: Article
Additional information: 0022-2836 (Print) Journal Article
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: Michael Geeves
Date Deposited: 16 Mar 2009 16:38
Last Modified: 28 Apr 2014 15:38
Resource URI: https://kar.kent.ac.uk/id/eprint/13214 (The current URI for this page, for reference purposes)
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