Role of myosin light-chain phosphorylation in guinea pig gallbladder smooth muscle contraction

R. J. Washabau, M. B. Wang, C. Dorst, J. P. Ryan

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10-8 M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K+- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32% of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist. Because myosin is stably phosphorylated during the period of steady-state isometric stress, these data also suggest that cross-bridge dephosphorylation is not necessary for the slowing of cross-bridge cycling rates in gallbladder smooth muscle. Thus, although myosin light-chain phosphorylation is essential in the initiation of contraction of gallbladder smooth muscle, factors other than myosin light-chain phosphorylation are involved in the regulation of cross- bridge cycling rates at steady state.

Original languageEnglish (US)
JournalAM.J.PHYSIOL.
Volume266
Issue number3 29-3
StatePublished - 1994

Fingerprint

Myosin Light Chains
Muscle Contraction
Gallbladder
Smooth Muscle
Guinea Pigs
Phosphorylation
Myosins
Acetylcholine
Sincalide
Cholecystokinin
Maintenance

Keywords

  • acetylcholine
  • calcium
  • cholecystokinin
  • cross-bridge cycling
  • latch bridges
  • muscle contraction
  • potassium

Cite this

Role of myosin light-chain phosphorylation in guinea pig gallbladder smooth muscle contraction. / Washabau, R. J.; Wang, M. B.; Dorst, C.; Ryan, J. P.

In: AM.J.PHYSIOL., Vol. 266, No. 3 29-3, 1994.

Research output: Contribution to journalArticle

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abstract = "In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10-8 M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K+- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32{\%} of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist. Because myosin is stably phosphorylated during the period of steady-state isometric stress, these data also suggest that cross-bridge dephosphorylation is not necessary for the slowing of cross-bridge cycling rates in gallbladder smooth muscle. Thus, although myosin light-chain phosphorylation is essential in the initiation of contraction of gallbladder smooth muscle, factors other than myosin light-chain phosphorylation are involved in the regulation of cross- bridge cycling rates at steady state.",
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N2 - In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10-8 M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K+- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32% of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist. Because myosin is stably phosphorylated during the period of steady-state isometric stress, these data also suggest that cross-bridge dephosphorylation is not necessary for the slowing of cross-bridge cycling rates in gallbladder smooth muscle. Thus, although myosin light-chain phosphorylation is essential in the initiation of contraction of gallbladder smooth muscle, factors other than myosin light-chain phosphorylation are involved in the regulation of cross- bridge cycling rates at steady state.

AB - In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10-8 M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K+- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32% of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist. Because myosin is stably phosphorylated during the period of steady-state isometric stress, these data also suggest that cross-bridge dephosphorylation is not necessary for the slowing of cross-bridge cycling rates in gallbladder smooth muscle. Thus, although myosin light-chain phosphorylation is essential in the initiation of contraction of gallbladder smooth muscle, factors other than myosin light-chain phosphorylation are involved in the regulation of cross- bridge cycling rates at steady state.

KW - acetylcholine

KW - calcium

KW - cholecystokinin

KW - cross-bridge cycling

KW - latch bridges

KW - muscle contraction

KW - potassium

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