Ca²⁺ activity during ATP-induced relaxation of porcine retinal arterioles in vitro spreads along the processes of the perivascular cells

Abstract

Purpose : Recently, a novel population of perivascular cells (PVC) located immediately external to the vascular smooth muscle cells of retinal arterioles has been identified. These cells display Ca²⁺ activity simultaneously with relaxation of retinal arterioles and are connected to cellular processes extending into the retinal tissue. It has also been shown that retinal arterioles with intermediate contraction have a biphasic response to ATP with an initial contraction followed by a relaxation. The aim of this study was to investigate Ca²⁺ signals in PVCs and their process during successive contraction and relaxation of retinal arterioles induced by ATP.

Methods : Porcine retinal arterioles with preserved perivascular retinal tissue were mounted in a confocal myograph and loaded with the Ca²⁺-sensitive fluorophore Oregon Green. The arterioles were preconstricted with 10^-7 – 10^-6 M U46619, and after the addition of ATP (10^-4 M) vascular tone was recorded in a wire myograph and intracellular fluorescence in a laser scanning confocal microscope.

Results : The addition of ATP induced Ca²⁺ waves in PVCs (n=32) and their processes (n=7) both during contraction and relaxation of retinal arterioles. There was no significant difference between the frequency of Ca²⁺ waves in PVCs and their processes during contraction and relaxation (p>0.05), but the amplitude of Ca²⁺ waves was significantly higher (p<0.01) during contraction than during relaxation in the two structures.

Conclusions : The amplitude of Ca²⁺ waves in perivascular cells and their processes might potentially be used to differentiate contracting and relaxing responses of retinal arterioles.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.