Abstract
A synthetic peptide of the inhibitory region of cardiac troponin I [136 - 147] (troponin I inhibitory peptide; TnIp) suppresses Ca ion induced contraction of smooth muscle preparations skinned with beta-escin via direct interference with actin-myosin interaction (Watanabe et al., BBRC 307, 236-40, 2003). To analyse TnIp action on the cross-bridge cycling in detail, we studied TnIp effects on the relaxation of skinned taenia caeci smooth muscle induced by the Ca ion removal with EGTA. In the presence of TnIp at more than 100 micro molar, the tension did not fall to the resting level completely, but instead reached a sustained force maintaining level. Data analysis of the time course of the relaxation indicated TnIp accelerating transformation of rapid- to slow-cross-bridge cycling. These results suggest that thin-filament-liked regulatory systems in smooth muscle may contribute "latch" cross-bridge formation. [Jpn J Physiol 54 Suppl:S125 (2004)]
