Abstract
TnIp, a synthetic peptide originating from an actin tropomyosin binding region of rabbit cardiac troponin I [residues 136-147; GKFKRPTLRRVR], had biphasic effects on the relaxation of skinned smooth muscle, as accelerating the initial phase and slowing the following latter phase of the relaxation, resulted from accelerating fast cross-bridge dissociation and also transformation from fast to slow (latch) cross-bridges (Watanabe et al., 2004). To evaluate the contribution of each amino acid residue of TnIp to its biphasic effects on the relaxation, we compared the effects of 11 TnIp analogues, which consisted of single glycine replacement, on the relaxation time course by lowering Ca2+ concentration in contracting skinned taenia caeci from guinea pig. Replacing K137, F138, K139, R140, T142, L143, R144, or R145 for glycine resulted in loss of the accelerating effect of TnIp on the fast cross-bridge dissociation, seeming that the entire residues of TnIp might be necessary for acceleration of the cross-bridge dissociation by TnIp. On the other hand, the enhancing effect of TnIp on the translation from fast cross-bridges to latch bridges was kept except only when R147 was substituted for glycine. R147 seems to be a key residue for regulation of latch bridge formation by TnIp. [J Physiol Sci. 2006;56 Suppl:S144]
