Stretch-induced triphosphorylation of myosin light chain and myogenic tone in canine basilar artery

Abstract

The relationship between phosphorylation of 20,000 Da myosin light chain (MLC 20) and contraction in response to mechanical stretch was investigated in the canine basilar artery. A slow stretch (at a rate of 1 mm/s and a stimulus period for 15 min) increased triphosphorylated MLC 20 despite lowered intracellular calcium concentration and mechanical activities, such as myogenic tone, shortening velocity and stiffness of the artery. Nicardipine, a Ca 2+ channel blocker, and ML-9, a myosin light chain kinase (MLCK) inhibitor, partially inhibited the stretch-induced MLC 20 phosphorylation. The remained phosphorylation was further reduced by calphostin C, a protein kinase C (PKC) inhibitor. Y-27632, a Rho-kinase inhibitor, inhibited phosphorylation of myosin light chain phosphatase and attenuated MLC 20 phosphorylation. These results suggest that slow stretch induces triphosphorylation of MLC 20, which is mediated by MLCK, PKC, and Rho-kinase, and that the triphosphorylation of MLC 20 does not result in myogenic contraction, rather seems to counteract it.