Cross-bridge kinetics during shortening in early and sustained contraction of intestinal smooth muscle

Hellstrand, PerLund University,Lunds universitet,Kärlfysiologi,Forskargrupper vid Lunds universitet,Vascular Physiology,Lund University Research Groups (author)

Mechanisms responsible for the decrease in shortening velocity after prolonged contraction ("latch" state) were investigated at identical force during early (20 s, "phasic") and sustained (5 min, "tonic") phases of high-K+ (25-30 mM) contractions in smooth muscle of guinea pig taenia coli. Cytoplasmic Ca2+ concentration, myosin light-chain phosphorylation, and maximum shortening velocity all declined from 20 s to 5 min of contraction. The time course of shortening following isotonic quick release was biexponential, with a fastest rate constant of approximately 80 s-1 in both phasic and tonic contractions. Stiffness was identical in phasic and tonic contraction; however, after a release to slack length and unloaded shortening, stiffness during restretch was greater in tonic contraction (51 vs. 43% of isometric stiffness after 16 ms of unloaded shortening). Stiffness decreased after release with a rate constant of approximately 200 s-1, slightly greater in phasic than in tonic contraction. The results indicate that the number of attached cross bridges during unloaded shortening, while substantially reduced relative to the isometric value, is higher in latch than in nonlatch, consistent with a lower detachment relative to attachment rate.

Nordström, InaLund University,Lunds universitet,Kärlfysiologi,Forskargrupper vid Lunds universitet,Vascular Physiology,Lund University Research Groups(Swepub:lu)mphy-ino (author)
KärlfysiologiForskargrupper vid Lunds universitet (creator_code:org_t)

In:American Journal of Physiology: Cell Physiology265:3 Pt 1, s. 695-7031522-1563

About the subject

MEDICAL AND HEALTH SCIENCES: MEDICAL AND HEAL ...; and Basic Medicine; and Physiology

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