The Japanese Journal of Physiology
Print ISSN : 0021-521X
Synthetic Peptides of Actin-Tropomyosin Binding Region of Troponin I and Heat Shock Protein 20 Modulate the Relaxation Process of Skinned Preparations of Taenia Caeci from Guinea Pig
Yasumasa YoshinoWataru SakuraiSachio MorimotoMasaru Watanabe
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JOURNAL FREE ACCESS Advance online publication

Article ID: 0601180023


To explore the possible role of thin filament–linked regulation of cross-bridge cycling in living smooth muscle contraction, we studied the effects of TnIp and HSP20p, a synthetic peptide originating from an actin tropomyosin binding region of rabbit cardiac troponin I (residues 136–147; GKFKRPTLRRVR), and that of human heat shock protein 20 (residues 110–121; GFVAREFHRRYR) respectively, on relaxation of skinned (cell membrane permeabilised) preparations from guinea pig taenia caeci. Active stress of the skinned preparations, resulting from actin–myosin interaction, rapidly decayed following Ca2+ removal (relaxation). TnIp accelerated the initial rapid phase and slowed the following slow phase of the relaxation. On the other hand, HSP20p only slowed the whole process of the relaxation. The relaxation time courses were well fitted in a double exponential manner, and the double exponential decay of the stress could be explained as a portion of fast detaching cross-bridges not to dissociate rapidly by Ca2+ removal, but to transfer to latch-bridges dissociating very slowly. Our present results suggested that, (i) TnIp and HSP20p accelerated transferring from fast-detaching cross-bridges to slow-detaching (latch) bridges, and (ii) TnIp accelerated dissociation of the fast-detaching cross-bridges and the latch-bridges, while HSP20p slowed the fast detaching cross-bridges. Since TnIp and HSP20p are thought to bind to actin, and tropomyosin, but not to myosin, we concluded that, through thin-filament–dependent mechanisms, these peptides regulated the formation and/or deformation of latch bridges in smooth muscle. The thin-filament–dependent regulation might physiologically control the stress maintenance and relaxation in smooth muscle cells.

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