Novel PKC pathway provides insight into the regulation of tone in vascular smooth muscle (865.13)

Vascular smooth muscle (VSM) tone is the phenomenon of intrinsic force developed in the absence of a stimulus. Although the primary site of VSM regulation is on the thick filament, our research has focused on the potential role of thin filament proteins in signaling events contributing to vascular tone. We hypothesized that protein kinase C (PKC)‐dependent phosphorylation of mitogen‐activated protein kinase phosphatase‐1 (MKP‐1), an upstream mitogen activated protein kinase (MAPK) regulatory protein, would increase MKP‐1 activity and decrease MAPK activity. We used the MKP‐1 inhibitor, sanguinarine, to investigate the effect of PKC on p42/p44 MAPK in swine arterial smooth muscle. Smooth muscle strips were mounted for isometric force measurement and incubated with 3 µM Bis (PKC inhibitor), 10 µM histamine, or both, in the presence or absence of 30 µM sanguinarine. Histamine significantly increased p42/p44 MAPK activity; the p42 isoform was further enhanced by inhibition of PKC. Sanguinarine reversed the histamine and Bis‐dependent increases in p42 MAPK. MKP‐1 phosphorylation was increased by histamine and Bis, and surprisingly was further amplified in the presence of sanguinarine. These findings suggest a novel PKC pathway, which indirectly modulates MAPK activity through phosphorylation of MKP‐1. Our current studies are examining potential regulatory proteins as downstream sites of action by MAPK. Grant Funding Source : NIH DK 85734