Basic study on cerebral vasospasm: Ca2+ movement during contraction-relaxation of isolated basilar arteries.

Abstract

To establish a definitive therapy for cerebral vasospasm, a basic study on the contractile mechanism of vascular smooth muscles of the cerebral artery was performed. Ultrastructural examination of smooth muscle cells in bovine basilar arteries revealed the existence of two types of myofilaments which correspond to thick and thin filaments. Also, the existence of an internal membrane system just inside of the surface membrane was confirmed. Experiments on the mechanical activity of basilar arterial strips showed that a K+ induced contraction was associated with a large increase of Ca2+ influx from outside of the muscle cell. On the other hand, 5HT induced tension without Ca2+ influx. A Ca antagonist (cinnarizine or verapamil) inhibited high K+ induced contractions, whereas its inhibitory effect on 5HT induced contraction was small. These facts suggest that 5HT can release Ca from intracellular store sites. The results shown here indicate that there are several kinds of bound Ca in the muscle cell, i.e.: 1) loosely; and 2) tightly bound Ca on the external surface of the cell membrane; 3) Ca bound in the internal surface of the cell membrane; and 4) Ca stored in the intracellular store sites, such as sarcoplasmic reticulum or mitochondria. It is suggested that such intracellularly immobilized Ca may play an important role in the regulation of mechanical activity of cerebral arterial muscle.