Endothelium‐dependent frequency modulation of Ca2+ signalling in individual vascular smooth muscle cells of the rat

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Abstract
1 We visualized intracellular Ca2+ concentration ([Ca2+]i) changes, using fluo‐3 as an indicator, of individual vascular smooth muscle cells and endothelial cells within intact rat tail arteries by confocal microscopy. 2 Using a piezo‐driven objective, we focused on endothelial and smooth muscle cell layers alternately to obtain Ca2+ images of their cells. In the presence of 1 μm acetylcholine (ACh), individual endothelial cells responded with intermittent increases in the [Ca2+]i (Ca2+ oscillations). At the same time, the frequency of Ca2+ oscillations in smooth muscle cells induced by electrical stimulation of the perivascular sympathetic nerve was greatly decreased. 3 A [Ca2+]i rise during the oscillations in the endothelial cells propagated in the form of a wave along the long axis of the cells. 4 In the presence of a NO synthase inhibitor, no significant inhibitory effect of ACh on the Ca2+ signalling in the vascular smooth muscle cells was detected, although the Ca2+ oscillations in the endothelial cells persisted. 5 The inhibitory effect of ACh on the frequency of Ca2+ oscillations in the vascular smooth muscle cells was mimicked by 1 μm sodium nitroprusside, a NO donor. 6 These results indicate that Ca2+ waves and oscillations in vascular endothelial cells regulate NO production, which modulates vascular tone by decreasing the frequency of Ca2+ oscillations in smooth muscle cells activated by sympathetic agonists.