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Thick-to-thin filament surface distance modulates cross-bridge kinetics in Drosophila flight muscle.

Abstract：

:The demembranated (skinned) muscle fiber preparation is widely used to investigate muscle contraction because the intracellular ionic conditions can be precisely controlled. However, plasma membrane removal results in a loss of osmotic regulation, causing abnormal hydration of the myofilament lattice and its proteins. We investigated the structural and functional consequences of varied myofilament lattice spacing and protein hydration on cross-bridge rates of force development and detachment in Drosophila melanogaster indirect flight muscle, using x-ray diffraction to compare the lattice spacing of dissected, osmotically compressed skinned fibers to native muscle fibers in living flies. Osmolytes of different sizes and exclusion properties (Dextran T-500 and T-10) were used to differentially alter lattice spacing and protein hydration. At in vivo lattice spacing, cross-bridge attachment time (t(on)) increased with higher osmotic pressures, consistent with a reduced cross-bridge detachment rate as myofilament protein hydration decreased. In contrast, in the swollen lattice, t(on) decreased with higher osmotic pressures. These divergent responses were reconciled using a structural model that predicts t(on) varies inversely with thick-to-thin filament surface distance, suggesting that cross-bridge rates of force development and detachment are modulated more by myofilament lattice geometry than protein hydration. Generalizing these findings, our results suggest that cross-bridge cycling rates slow as thick-to-thin filament surface distance decreases with sarcomere lengthening, and likewise, cross-bridge cycling rates increase during sarcomere shortening. Together, these structural changes may provide a mechanism for altering cross-bridge performance throughout a contraction-relaxation cycle.

journal_name

Biophys J

journal_title

Biophysical journal

authors

Tanner BC,Farman GP,Irving TC,Maughan DW,Palmer BM,Miller MS

doi

10.1016/j.bpj.2012.08.014

subject

Has Abstract

pub_date

2012-09-19 00:00:00

pages

1275-84

issue

eissn

0006-3495

issn

1542-0086

pii

S0006-3495(12)00875-2

journal_volume

103

pub_type

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Thick-to-thin filament surface distance modulates cross-bridge kinetics in Drosophila flight muscle.