Ca2+ activity during ATP‐induced tone changes in porcine retinal arterioles in vitro spreads along the processes of perivascular cells

PurposeRecently, 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 tone changes of retinal arterioles and have processes extending into the retina. This data suggests that PVCs could play a role in the neurovascular coupling in the retina. The aim of the study was to investigate Ca2+ signals in PVCs and their processes during successive contraction and relaxation of retinal arterioles induced by ATP.MethodsFirst order 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 5*10‐8 – 10‐6 M U46619 and after the addition of ATP (10‐4 M) intracellular fluorescence from the PVC layer was recorded by a confocal microscope simultaneously with the vascular tone.ResultsATP induced a biphasic tone response in 19% (5 out of 26) of the studies arterioles. The tone response consisted of 15 ± 4% initial contraction followed by 30 ± 20% relaxation. ATP induced Ca2+ waves in 49 ± 16% PVCs and 46 ± 14% processes during the contraction and in 46 ± 16% PVCs and 46 ± 14% processes during the relaxation. 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.ConclusionsPVC Ca2+ waves associated with contraction and relaxation of porcine retinal arterioles spread along cellular processes. The amplitude of Ca2+ waves in PVCs and their processes can be used to differentiate contracting and relaxing responses of retinal arterioles.