Novel cellular bouton structure activated by ATP in the vascular wall of porcine retinal arterioles.
OBJECTIVE
The retinal blood flow is regulated by the tone of resistance arterioles, which is influenced by purinergic compounds such as adenosine and adenosine 5'-triphosphate (ATP) released from the retinal tissue. However, it is unknown what cellular elements in the perivascular retina are responsible for the effect of purines on the tone of retinal arterioles.


METHODS
Porcine retinal arterioles were loaded with the calcium-sensitive fluorophore Oregon green. The vessels were mounted in a confocal myograph for simultaneous recordings of tone and calcium activity in cells of the vascular wall during stimulation with ATP and adenosine, with and without modifiers of these compounds. Additionally, immunohistochemistry was used to localize elements with calcium activity in the vascular wall.


RESULTS
Hyperfluorescence indicating calcium activity was recorded in a population of abundant round boutons interspersed in a network of vimentin-positive processes located immediately external to the smooth muscle cell layer but internal to the perivascular glial cells. These structures showed calcium activity when the vessel was relaxed with ATP but not when it was relaxed with adenosine. Ryanodine reduced calcium activity in the boutons, whereas the ATP antagonist adenosine-5'-O-(α, β- methylene diphosphate) reduced calcium activity in both the boutons and vascular tone.


CONCLUSIONS
The vasodilating effect of purines in porcine retinal tissue involves ATP-dependent calcium activity in a layer of cellular boutons located external to the vascular smooth muscle cells and internal to the perivascular glial cells.
Misfeldt
Mikkel Wölck
MW
Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. mikkel.misfeldt@ki.au.dk
Aalkjaer
Christian
C
Simonsen
Ulf
U
Bek
Toke
T
D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D022082:Cellular Structures / Q000166:cytology* / Q000378:metabolism; D024141:Collagen Type IV / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009213:Myography; D012161:Retinal Artery / Q000187:drug effects*; D009418:S100 Proteins / Q000378:metabolism; D013552:Swine; D016708:Synaptophysin / Q000378:metabolism; D014746:Vimentin / Q000378:metabolism
D000199:Actins; D024141:Collagen Type IV; D005904:Glial Fibrillary Acidic Protein; D009418:S100 Proteins; D016708:Synaptophysin; D014746:Vimentin; D000255:Adenosine Triphosphate; D002118:Calcium