NDLI: Activation of skinned trabeculae of the guinea pig induced by laser photolysis of caged ATP.

Content Provider	PubMed Central
Author	Martin, H. Barsotti, R. J.
Abstract	The kinetics of force production in chemically skinned trabeculae from the guinea pig were studied by laser photolysis of caged ATP in the presence of Ca2+. Preincubation of the tissue during rigor with the enzyme apyrase was used to reduce the population of MgADP-bound cross-bridges (Martin and Barsotti, 1994). In untreated tissue, tension remained constant or dipped slightly below the rigor level immediately after ATP release, before increasing to the maximum measured in pCa 4.5 and 5 mM MgATP. The in-phase component stiffness, which is a measure of cross-bridge attachment, exhibited a large decrease before increasing to 55% of that measured in rigor. Neither the rate of the decline nor of the rise in tension was sensitive to the concentration of photolytically released ATP. The rate of the decline in stiffness was found to be dependent on [ATP]: 1.8 x 10(4) M-1/s-1, a value more than four times higher than that previously measured in similar experiments in the absence of Ca2+. The rate of tension development averaged 14.9 +/- 2.5 s-1. Preincubation with apyrase altered the mechanical characteristics of the early phase of the contraction. The rate and amplitude of the initial drop in both tension and stiffness after caged ATP photolysis increased and became dependent on [ATP]. The second-order rate constants measured for the initial drop in tension and stiffness were 8.4 x 10(4) M-1 s-1 and 1.5 x 10(5) M-1 s-1. These rates are more than two times faster than those previously measured in the absence of Ca2+. The effects of apyrase incubation on the time course of tension and stiffness were consistent with the hypothesis that during rigor, skinned trabeculae retain a significant population of MgADP-bound cross-bridges. These in turn act to attenuate the initial drop in tension after caged ATP photolysis and slow the apparent rate of rigor cross-bridge detachment. The results also show that Ca2+ increases the rate of cross-bridge detachment in both untreated and apyrase-treated tissue, but the effect is larger in untreated tissue. This suggests that in cardiac muscle Ca2+ modulates the rate of cross-bridge detachment.
Related Links	http://dx.doi.org/10.1016/s0006-3495(94)80676-9
Ending Page	1941
Page Count	9
Starting Page	1933
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	5
Volume Number	67
Language	English
Publisher Date	1994-11-01
Access Restriction	Open
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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