Differential effects of a K + channel agonist and Ca 2+ antagonists on myosin light chain phosphorylation in relaxation of endothelin-1-contracted tracheal smooth muscle

It is generally assumed that relaxation of arteriolar vascular smooth muscle occurs through hyperpolarization of the cell membrane, reduction in intracellular Ca2+ concentration, and activation of myosin light chain phosphatase/inactivation of myosin light chain kinase. We hypothesized that vasodilation is related to depolymerization of F-actin. Cremaster muscles were dissected in rats under pentobarbital sodium anesthesia (50 mg/kg). First-order arterioles were dissected, cannulated on glass micropipettes, pressurized, and warmed to 34°C. Internal diameter was monitored with an electronic video caliper. The concentration of G-actin was determined in flash-frozen intact segments of arterioles by ultracentrifugation and Western blot analyses. Arterioles dilated by ~40% of initial diameter in response to pinacidil (1 × 10−6 mM) and sodium nitroprusside (5 × 10−5 mM). The G-actin-to-smooth muscle 22α ratio was 0.67 ± 0.09 in arterioles with myogenic tone and increased significantly to 1.32 ± 0.34 ( P < 0.01) when arterioles were dilated with pinacidil and 1.14 ± 0.18 ( P < 0.01) with sodium nitroprusside, indicating actin depolymerization. Compared with control vessels (49 ± 5%), the percentage of phosphorylated myosin light chain was significantly reduced by pinacidil (24 ± 2%, P < 0.01) but not sodium nitroprusside (42 ± 4%). These findings suggest that actin depolymerization is an important mechanism for vasodilation of resistance arterioles to external agonists. Furthermore, pinacidil produces smooth muscle relaxation via both decreases in myosin light chain phosphorylation and actin depolymerization, whereas sodium nitroprusside produces smooth muscle relaxation primarily via actin depolymerization. NEW & NOTEWORTHY This article adds to the accumulating evidence on the contribution of the actin cytoskeleton to the regulation of vascular smooth muscle tone in resistance arterioles. Actin depolymerization appears to be an important mechanism for vasodilation of resistance arterioles to pharmacological agonists. Dilation to the K+ channel opener pinacidil is produced by decreases in myosin light chain phosphorylation and actin depolymerization, whereas dilation to the nitric oxide donor sodium nitroprusside occurs primarily via actin depolymerization. Listen to this article’s corresponding podcast at https://ajpheart.podbean.com/e/vascular-smooth-muscle-actin-depolymerization/ .

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Intrinsic circadian oscillation of myosin light chain phosphorylation in vascular smooth muscle cells

The FASEB Journal ◽

10.1096/fasebj.24.1_supplement.985.14 ◽

2010 ◽

Vol 24 (S1) ◽

Author(s):

Toshiro Saito ◽

Mayumi Hirano ◽

Tomomi Ide ◽

Kenji Sunagawa ◽

Katsuya Hirano

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Light Chain ◽

Myosin Light Chain ◽

Muscle Cells ◽

Circadian Oscillation ◽

Myosin Light Chain Phosphorylation

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Mechanism of galanin-induced contraction of longitudinal smooth muscle of the rat jejunum

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1998.274.2.g306 ◽

1998 ◽

Vol 274 (2) ◽

pp. G306-G313 ◽

Cited By ~ 2

Author(s):

Simon A. Ahtaridis ◽

Surender S. Katoch ◽

Robert S. Moreland

Keyword(s):

Smooth Muscle ◽

Pertussis Toxin ◽

Light Chain ◽

Myosin Light Chain ◽

Effective Concentration ◽

Rat Jejunum ◽

Myosin Light Chain Phosphorylation ◽

Half Maximum ◽

Longitudinal Smooth Muscle ◽

Intracellular Ca

Intact and α-toxin-permeabilized longitudinal smooth muscle were mounted for measurement of force and myosin light chain phosphorylation. Galanin contracted intact jejunum with a half-maximum effective concentration of 9.2 ± 0.1 nM. Neither atropine, hexamethonium, guanethidine, nor tetrodotoxin affected the contraction. The contraction was also unaffected by depletion of intracellular Ca2+ or by addition of thapsigargin; removal of extracellular Ca2+ or addition of nifedipine abolished the contraction. Galanin increased myosin light chain phosphorylation levels concomitantly with force. During continued tissue stimulation, force fell to suprabasal values, whereas myosin light chain phosphorylation levels remained elevated. Galanin increased Ca2+ sensitivity of contraction in α-toxin-permeabilized tissues, and this was reversed by either guanosine 5′- O-(2-thiodiphosphate) or pertussis toxin. These results suggest that galanin-induced contraction of longitudinal jejunal smooth muscle is dependent on a pertussis toxin-sensitive G protein that is apparently not coupled to the release of intracellular Ca2+but to the influx of extracellular Ca2+ and involves an initial myofilament Ca2+ sensitization followed by Ca2+ desensitization.

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