Abstract:
:In maximally activated skinned fibers, the rate of tension redevelopment (ktr) following a rapid release and restretch is determined by the maximal rate of cross-bridge cycling. During submaximal Ca2+ activations, however, ktr regulation varies with thin filament dynamics. Thus, decreasing the rate of Ca2+ dissociation from TnC produces a higher ktr value at a given tension level (P), especially in the [Ca2+] range that yields less than 50% of maximal tension (Po). In this study, native rabbit TnC was replaced with chicken recombinant TnC, either wild-type (rTnC) or mutant (NHdel), with decreased Ca2+ affinity and an increased Ca2+ dissociation rate (koff). Despite marked differences in Ca2+ sensitivity (>0.5 DeltapCa50), fibers reconstituted with either of the recombinant proteins exhibited similar ktr versus tension profiles, with ktr low (1-2 s-1) and constant up to approximately 50% Po, then rising sharply to a maximum (16 +/- 0.8 s-1) in fully activated fibers. This behavior is predicted by a four-state model based on coupling between cross-bridge cycling and thin filament regulation, where Ca2+ directly affects only individual thin filament regulatory units. These data and model simulations confirm that the range of ktr values obtained with varying Ca2+ can be regulated by a rate-limiting thin filament process.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Regnier M,Rivera AJ,Chase PB,Smillie LB,Sorenson MMdoi
10.1016/S0006-3495(99)77418-7subject
Has Abstractpub_date
1999-05-01 00:00:00pages
2664-72issue
5eissn
0006-3495issn
1542-0086pii
S0006-3495(99)77418-7journal_volume
76pub_type
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