ISSN:
1432-2013
Keywords:
Key words Protein kinase C
;
Phorbol ester
;
Vascular smooth muscle
;
Myosin light chain kinase
;
Myosin light chain phosphorylation
;
Phosphatase
;
Arachidonic acid
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract We investigated the role of 20 kDa myosin light chain (MLC20) phosphorylation in contractions following protein kinase C (PKC) activation by 12-deoxyphorbol-13-isobutyrate (DPB) in rabbit aortae. DPB induced a sustained contraction and phosphorylation of MLC20 independent of a change in cytosolic Ca2+ ([Ca2+]i). Phosphorylation on Ser19 of MLC20, which is a target site of MLC kinase (MLCK), was 9.2 ± 5.1% and 22.3 ± 4.9% of the phosphorylation caused by KCl, at 5 and 30 min of application of DPB, respectively. When KCl-precontracted muscles were rinsed with Ca2+-free, EGTA solution, [Ca2+]i rapidly declined, MLC20 was dephosphorylated and the tension decreased. If DPB was present in the Ca2+-free solution, the relaxation and the dephosphorylation of either total MLC20 or Ser19 were inhibited. The phospholipase A2 inhibitor ONO-RS-082 partially antagonized the effects of DPB on the tension and the MLC20 dephosphorylation. In Ca2+-free solution, DPB induced a contraction smaller than that in normal solution without an increase in MLC20 phosphorylation, and the contraction was also sensitive to ONO-RS-082. These results suggest that a part of MLC20 phosphorylation following PKC activation is due to inhibition of MLC20 phosphatase and the phosphorylation is responsible for the contraction. Furthermore, a mechanism independent of [Ca2+]i and phosphorylation may play a significant role in the PKC-dependent contraction. The involvement arachidonic acid is suggested, not only in the inhibition of dephosphorylation but also in the Ca2+-independent regulation of contractile proteins.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004240050452
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