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Energetic cost of activation processes during contraction of swine arterial smooth muscle
Author(s) -
Wingard Christopher J.,
Paul Richard J.,
Murphy Richard A.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.213bo.x
Subject(s) - phosphorylation , dephosphorylation , contraction (grammar) , isometric exercise , stimulation , chemistry , myosin , biophysics , myosin light chain kinase , biology , medicine , endocrinology , biochemistry , phosphatase
1 The objective of this study was to partition the increase in ATP consumption during contraction of swine carotid arterial smooth muscle estimated from suprabasal oxygen consumption (suprabasal J O 2 ) and lactate release ( J lactate ) into a component associated with cross‐bridge cycling ( J x ) and one reflecting activation ( J A ). 2 Two experimental approaches – varying length under constant activation, and varying activation at a long length (1.8 times the optimal length for force development (L 0 )) where force generation is minimal – revealed a linear dependence of J 0 and activation energy ( J A ) on cross‐bridge phosphorylation. Protocols inducing a large increase in myosin regulatory light chain (MRLC) phosphorylation at 1.8 L 0 resulted in significant elevations of J O 2 and marked reductions in the economy of force maintenance. Our evidence suggests that this is primarily due to the increased cost of cross‐bridge phosphorylation. 3 The extrapolated estimate of J A during maximal K + ‐induced depolarization made by varying length was 16%, while at 1.8 L O it was 33% of the suprabasal J O 2 at L 0 . Calculated activation energies ranged from 17 to 45% of the suprabasal J O 2 at L 0 and from 72 to 87% of the suprabasal J O 2 at 1.8 L 0 under stimulation conditions that varied steady‐state MRLC phosphorylation from 15 to 50%. 4 The results suggest that the kinetics of cross‐bridge phosphorylation‐dephosphorylation can rival those of cross‐bridge cycling during isometric contractions in swine arterial smooth muscle.