Myosin Light Chain Phosphorylation and Contractile Proteins in a Canine Two-Hemorrhage Model of Subarachnoid Hemorrhage

Abstract

Background and Purpose —Subarachnoid hemorrhage (SAH) impairs both contraction and relaxation response in cerebral arteries. We tested the hypothesis that cerebral vasospasm might be ATP-independent contraction, such as latch state, and protein synthesis might be substantially downregulated due to ATP consumption after long-lasting contraction. Methods —Chronic cerebral vasospasm was induced in the canine 2-hemorrhage model of SAH. The normal and spastic basilar arteries were stabilized in Krebs-Henseleit solution, and contraction was induced by 30 μmol/L prostaglandin F 2α (PGF 2α ) in vitro and in vivo. Before and at 15 minutes and 1 hour after the treatment with PGF 2α , the levels of phosphorylated 20-kDa myosin light chain (MLC 20 ) were measured. The time course of expression of contraction proteins actin and MLC 20 , and contraction-inhibiting proteins h -caldesmon and calponin was determined by immunoblotting techniques. Results —A significant vasospasm occurred in the basilar artery during days 4 to 21, most prominently on days 7 and 14. There were no significant differences in the baseline levels of phosphorylated MLC 20 between normal and spastic basilar arteries. The increase in MLC 20 phosphorylation by PGF 2α was significantly attenuated in the spastic basilar artery in vitro and in vivo ( P <0.05). The immunoreactivity for actin, h -caldesmon, and calponin in the spastic basilar arteries was progressively decreased until day 14 and returned to the normal level on day 21. In contrast, protein levels of MLC 20 did not significantly change during days 0 to 21. Conclusions —Chronic cerebral vasospasm closely resembles the latch state, and temporary deficiencies of contractile proteins may result from increased destruction and inhibition of protein synthesis.