Comparative Study of Calcium Ion Dynamics and Contractile Response in Rat Middle Cerebral and Basilar Arteries

Abstract

The objective of this study was to compare intracellular calcium concentration ([Ca²⁺]_i) and contractile responses in isolated rat middle cerebral artery (MCA) with those in basilar artery (BA) employing real-time confocal laser microscopy. KCl elicited transient [Ca²⁺]_i elevation and sustained contraction in both arteries; moreover, nearly equal responses were evident in both arteries. Application of 5-hydroxytryptamine (5-HT), vasopressin (VP), and α,β-methylene adenosine 5'-triphosphate (α,β-me ATP) also induced elevation of [Ca²⁺]_i and contraction in both arteries. The maximum response of 5-HT and VP necessary to increase [Ca²⁺]_i and to constrict the MCA was less in comparison to the BA; however, a linear relationship emerged between the maximum response of [Ca²⁺]_i and that of contraction. Additionally, the slope of the correlation regression line of MCA was nearly identical to that of BA. On the other hand, cyclopiazonic acid (CPA)-induced Ca²⁺ release from store sites following contraction of MCA was distinct from that of BA. In MCA, velocity of [Ca²⁺]_i elevation in smooth muscle cells and Ca²⁺-wave propagation along smooth muscle cells induced by 5-HT were slower than those in BA. These observations revealed that different regions of arteries along the same cerebral tissue may display distinct [Ca²⁺]_i response; moreover, this difference may be one reason for the distinct contractile response.