This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.106.084608v1 91/11/4230    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lu, X. Articles by Kawai, M. Search for Related Content PubMed PubMed Citation Articles by Lu, X. Articles by Kawai, M.

Temperature-Dependence of Isometric Tension and Cross-Bridge Kinetics of Cardiac Muscle Fibers Reconstituted with a Tropomyosin Internal Deletion Mutant

Xiaoying Lu ^*, Larry S. Tobacman  and Masataka Kawai ^*

^* Department of Anatomy and Cell Biology, University of Iowa, Iowa City, Iowa; and Departments of Medicine and Physiology & Biophysics, University of Illinois at Chicago, Chicago, Illinois

Correspondence: Address reprint requests to Dr. Masataka Kawai, Tel.: 319-335-8102; E-mail: masataka-kawai{at}uiowa.edu.

The effect of temperature on isometric tension and cross-bridge kinetics was studied with a tropomyosin (Tm) internal deletion mutant AS-23Tm (Ala-Ser-Tm (47–123)) in bovine cardiac muscle fibers by using the thin filament extraction and reconstitution technique. The results are compared with those from actin reconstituted alone, cardiac muscle-derived control acetyl-Tm, and recombinant control AS-Tm. In all four reconstituted muscle groups, isometric tension and stiffness increased linearly with temperature in the range 5–40°C for fibers activated in the presence of saturating ATP and Ca²⁺. The slopes of the temperature-tension plots of the two controls were very similar, whereas the slope derived from fibers with actin alone had 40% the control value, and the slope from mutant Tm had 36% the control value. Sinusoidal analysis was performed to study the temperature dependence of cross-bridge kinetics. All three exponential processes A, B, and C were identified in the high temperature range (30–40°C); only processes B and C were identified in the mid-temperature range (15–25°C), and only process C was identified in the low temperature range (5–10°C). At a given temperature, similar apparent rate constants (2a, 2b, 2c) were observed in all four muscle groups, whereas their magnitudes were markedly less in the order of AS-23Tm < Actin < AS-Tm Acetyl-Tm groups. Our observations are consistent with the hypothesis that Tm enhances hydrophobic and stereospecific interactions (positive allosteric effect) between actin and myosin, but 23Tm decreases these interactions (negative allosteric effect). Our observations further indicate that tension/cross-bridge is increased by Tm, but is diminished by 23Tm. We conclude that Tm affects the conformation of actin so as to increase the area of hydrophobic interaction between actin and myosin molecules.

This article has been cited by other articles:

				P. P. de Tombe and G. J. M. Stienen Impact of temperature on cross-bridge cycling kinetics in rat myocardium J. Physiol., October 15, 2007; 584(2): 591 - 600. [Abstract] [Full Text] [PDF]