Abstract
The mechanisms contributing to serotonin (5‐HT)‐induced vasoconstriction of cerebral arteries are poorly characterized. This is important as abnormalities in control of cerebral blood flow by 5‐HT are implicated in subarachnoid hemorrhage and may be involved in migraine. Force generation by vascular smooth muscle cells depends on the balance of myosin light chain kinase (MLCK) and phosphatase (MLCP) activities that determine the level of myosin light chain (LC20) phosphorylation. Agonists that activate Rho kinase (ROK) and protein kinase C (PKC) can inhibit MLCP by phosphorylation of myosin light chain targeting subunit 1 (MYPT1) and CPI‐17, respectively. This inhibition of MLCP leads to increased phospho‐LC20 and force generation at constant [Ca2+]i, i.e. Ca2+ sensitization. Here, we have quantified LC20, MYPT1 and CPI‐17 phosphorylation in protein samples derived from pressurized segments of rat middle cerebral arteries using a novel, highly sensitive western blotting method. 5‐HT induced constriction and increased phospho‐LC20; both were reduced by ROK (H1152, 0.3 µM) or PKC (GF109203, 3 µM) inhibition. Phospho‐MYPT1 level was increased by 5‐HT, but not phospho‐CPI‐17. Our data indicate for the first time that Ca2+ sensitization via ROK‐mediated phosphorylation of MYPT1 resulting in enhanced LC20phosphorylation and force generation may contribute to 5‐HT‐induced cerebral vasoconstriction.
Published Version
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