NDLI: The endothermic ATP hydrolysis and crossbridge attachment steps drive the increase of force with temperature in isometric and shortening muscle

Content Provider	PubMed Central
Author	Offer, Gerald Ranatunga, K. W.
Copyright Year	2015
Abstract	The isometric tetanic tension of skeletal muscle increases with temperature because attached crossbridge states bearing a relatively low force convert to those bearing a higher force. It was previously proposed that the tension-generating step(s) in the crossbridge cycle was highly endothermic and was therefore itself directly targeted by changes in temperature. However, this did not explain why a rapid rise in temperature (a temperature jump) caused a much slower rate of rise of tension than a rapid length step. This led to suggestions that the step targeted by a temperature rise is not the tension-generating step but is an extra step in the attached pathway of the crossbridge cycle, perhaps located on a parallel pathway. This enigma has been a major obstacle to a full understanding of the operation of the crossbridge cycle. We have now used a previously developed mechano-kinetic model of the crossbridge cycle in frog muscle to simulate the temperature dependence of isometric tension and shortening velocity. We allowed all five steps in the cycle to be temperature-sensitive. Models with different starting combinations of enthalpy changes and activation enthalpies for the five steps were refined by downhill simplex runs and scored by their ability to fit experimental data on the temperature dependence of isometric tension and the relationship between force and shortening velocity in frog muscle. We conclude that the first tension-generating step may be weakly endothermic and that the rise of tension with temperature is largely driven by the preceding two strongly endothermic steps of ATP hydrolysis and attachment of M.ADP.Pi to actin. The refined model gave a reasonable fit to the available experimental data and after a temperature jump the overall rate of tension rise was much slower than after a length step as observed experimentally. The findings aid our understanding of the crossbridge cycle by showing that it may not be necessary to include an additional temperature-sensitive step.
Related Links	http://dx.doi.org/10.1113/jphysiol.2014.284992
Ending Page	2016
Page Count	20
Starting Page	1997
File Format	PDF
ISSN	00223751
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 8
Volume Number	593
Language	English
Publisher	BlackWell Publishing Ltd
Publisher Date	2015-04-15
Access Restriction	Open
Rights Holder	BlackWell Publishing Ltd
Subject Keyword	Physiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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