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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1991 Oct 15;88(20):9307–9310. doi: 10.1073/pnas.88.20.9307

G protein-mediated inhibition of myosin light-chain phosphatase in vascular smooth muscle.

T Kitazawa 1, M Masuo 1, A P Somlyo 1
PMCID: PMC52703  PMID: 1656467

Abstract

The mechanism of G protein-mediated sensitization of the contractile apparatus of smooth muscle to Ca2+ was studied in receptor-coupled alpha-toxin-permeabilized rabbit portal vein smooth muscle. To test the hypothesis that Ca2+ sensitization is due to inhibition of myosin light-chain (MLC) phosphatase activity, we measured the effect of guanosine 5'-[gamma-thio]triphosphate and phenylephrine on the rate of MLC dephosphorylation in muscles preactivated with Ca2+ and incubated in Ca(2+)- and ATP-free solution containing 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) to block MLC kinase activity. Guanosine 5'-[gamma-thio]triphosphate alone (300 microM) or in combination (3 microM) with phenylephrine decreased the rates of relaxation and dephosphorylation of MLC to about half of control values; this inhibition is sufficient to account for maximal G protein-mediated Ca2+ sensitization of MLC phosphorylation. The rate of thiophosphorylation of MLC with adenosine 5'-[gamma-thio]-triphosphate was not affected by guanosine 5'-[gamma-thio]triphosphate. We suggest that inhibition of protein phosphatase(s) by G protein(s) may have important regulatory functions.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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