Universität zu Köln

Lopez-Davila, Alfredo Jesus, Chalovich, Joseph M., Zittrich, Stefan, Piep, Birgit, Matinmehr, Faramarz, Malnasi-Csizmadia, Andras, Rauscher, Anna A., Kraft, Theresia, Brenner, Bernhard and Stehle, Robert (2020). Cycling Cross-Bridges Contribute to Thin Filament Activation in Human Slow-Twitch Fibers. Front. Physiol., 11. LAUSANNE: FRONTIERS MEDIA SA. ISSN 1664-042X

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Abstract

It has been shown that not only calcium but also strong binding myosin heads contribute to thin filament activation in isometrically contracting animal fast-twitch and cardiac muscle preparations. This behavior has not been studied in human muscle fibers or animal slow-twitch fibers. Human slow-twitch fibers are interesting since they contain the same myosin heavy chain isoform as the human heart. To explore myosin-induced activation of the thin filament in isometrically contracting human slow-twitch fibers, the endogenous troponin complex was exchanged for a well-characterized fast-twitch skeletal troponin complex labeled with the fluorescent dye N-((2-(Iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole (fsTn-IANBD). The exchange was approximate to 70% complete (n = 8). The relative contributions of calcium and strong binding cross-bridges to thin filament activation were dissected by increasing the concentration of calcium from relaxing (pCa 7.5) to saturating levels (pCa 4.5) before and after incubating the exchanged fibers in the myosin inhibitor para-aminoblebbistatin (AmBleb). At pCa 4.5, the relative contributions of calcium and strong binding cross-bridges to thin filament activation were approximate to 69 and approximate to 31%, respectively. Additionally, switching from isometric to isotonic contraction at pCa 4.5 revealed that strong binding cross-bridges contributed approximate to 29% to thin filament activation (i.e., virtually the same magnitude obtained with AmBleb). Thus, we showed through two different approaches that lowering the number of strong binding cross-bridges, at saturating calcium, significantly reduced the activation of the thin filament in human slow-twitch fibers. The contribution of myosin to activation resembled that which was previously reported in rat cardiac and rabbit fast-twitch muscle preparations. This method could be applied to slow-twitch human fibers obtained from the soleus muscle of cardiomyopathy patients. Such studies could lead to a better understanding of the effect of point mutations of the cardiac myosin head on the regulation of muscle contraction and could lead to better management by pharmacological approaches.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Lopez-Davila, Alfredo Jesus UNSPECIFIED UNSPECIFIED UNSPECIFIED Chalovich, Joseph M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Zittrich, Stefan UNSPECIFIED UNSPECIFIED UNSPECIFIED Piep, Birgit UNSPECIFIED UNSPECIFIED UNSPECIFIED Matinmehr, Faramarz UNSPECIFIED UNSPECIFIED UNSPECIFIED Malnasi-Csizmadia, Andras UNSPECIFIED UNSPECIFIED UNSPECIFIED Rauscher, Anna A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kraft, Theresia UNSPECIFIED UNSPECIFIED UNSPECIFIED Brenner, Bernhard UNSPECIFIED UNSPECIFIED UNSPECIFIED Stehle, Robert UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-340318
DOI:	10.3389/fphys.2020.00144
Journal or Publication Title:	Front. Physiol.
Volume:	11
Date:	2020
Publisher:	FRONTIERS MEDIA SA
Place of Publication:	LAUSANNE
ISSN:	1664-042X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language CARDIAC TROPONIN-C; SKELETAL-MUSCLE; MYOSIN SUBFRAGMENT-1; STRUCTURAL-CHANGES; CALCIUM SENSITIVITY; COOPERATIVE BINDING; KINETIC MECHANISM; FORCE GENERATION; REGULATED ACTIN; ATPASE ACTIVITY Multiple languages Physiology Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/34031