Differential regulation of intracellular Ca 2+ signalling induced by high K + and endothelin-1 in single smooth muscle cells of intact canine basilar artery: Detection by means of confocal laser microscopy

Abstract

Changes in intracellular calcium concentration ([Ca 2+]i) in smooth muscle cells play the key role in regulation of vascular smooth muscle tone and pathogenesis of cerebral vasospasm. In this study, we adopted the confocal laser microscopy to detect the fluorescence signals arising from the individual smooth muscle cells of canine basilar artery. Ring preparations were made, loaded with fluo-3 and changes in fluorescence induced by high K + and endothelin-1 (ET-1) were measured by confocal laser microscopy. In some unstimulated smooth muscle cells Ca 2+ waves arising from discrete region of the cell propagated to the whole cell with a velocity of ~10 μm/s. High K + (80 mmol/L) induced a rapid rise in [Ca 2+]i, the peak level being consistently reached approximately 10 s after stimulation. In contrast, the time to peak level of [Ca 2+]i induced by ET-1 (0.3 (μmol/L) varied widely between 13 and 26 s among individual cells, an indication that the extent of nonuniform coordination of increases in [Ca 2+]i in individual cells may be partly responsible for the different time courses of tension development of vascular smooth muscle in response to the vasoactive stimulants. The increase in [Ca 2+]i induced by ET-1 was transient but a pronounced and sustained contraction developed further in response to ET-1. Thus ET-1 has a biological property as a potential candidate to elicit cerebral vasospasm. Confocal laser microscopy could be a useful tool to measure the changes in [Ca 2+]i in individual smooth muscle cells of cerebral artery.