Experimental Study on Cerebral Vasospasm : Contractile Proteins in Smooth Muscle of Bovine Carotid Artery

Abstract

In order to understand the mechanism of the cerebral vasospasm that often follows rupture of an intracranial aneurysm, an experimental study on contractile and regulatory proteins in arterial smooth muscle was performed. Ca²⁺ sensitive myosin B was extracted from a bovine carotid artery and was separated into its components: myosin A, actin, tropomyosin and troponin. Electronmicrograph of the components revealed that: 1) Myosin A had a rod-like structure; its diameter and length were 150 and 3, 000 Å, respectively. 2) F-actin showed a helical structure with a pitch of about 390 Å. 3) Myosin B in low ionic strength, showed an arrowhead structure. 4) In a clearing response, thick and thin filaments (diameter: 150 Å and 80 Å, respectively) of myosin B were separated. 5) In a state of superpercipitaion, large aggregates of thick and thin filaments were observed. 6) Tropomyosin paracrystals showed a typical band structure; its periodicity was 390 Å. 7) Fresh myosin B exhibited Ca²⁺ sensitive superpercipitation. 8) In the desensitized myosin B, however, no superpercipitation was observed neither in the presence nor absence of Ca²⁺. 9) Addition of native tropomyosin and Ca²⁺ to this system caused definite superpercipitation. It is clear that the existence of native tropomyosin and Ca²⁺ are indispensable for the contraction of vascular smooth muscle.