Adenosine relaxation in small retinal arterioles requires functional Na-K pumps and K(ATP) channels.
OBJECTIVE
To study the effect of Na-K pump and K(ATP) channel inhibition on the diameter and the adenosine-induced vasodilation of small retinal arterioles.


METHODS
Thirty isolated porcine arterioles with a diameter of approximately 70 microm were mounted in a double-barrelled pipette system placed in an organ bath, and diameter changes were studied under isobaric no-flow conditions. After an equilibration period, the arterioles were incubated with the Na-K pump inhibitors ouabain and low K(+) medium or the K(ATP) channel inhibitor glibenclamide, and spontaneous diameter changes were studied. Subsequently, the arterioles were precontracted and the adenosine concentration response curve was measured with and without the presence of inhibitors.


RESULTS
Inhibition of the Na-K pump elicited a significant decrease in the spontaneous diameter of the vessels (P = 0.047), whereas no change in the spontaneous diameter was induced by inhibition of the K(ATP) channels (P = 0.754). Inhibition of the Na-K pump with ouabain or with low K(+) medium, as well as inhibition of the K(ATP) channels with glibenclamide, both diminished the adenosine induced vasodilation (P = 0.003, P = 0.01, and P = 0.003, respectively).


CONCLUSIONS
The adenosine-induced vasodilation of small retinal arterioles involves the K(ATP) channels and the Na-K pump. Changes in the metabolism of adenosine as well as the activity of the K(ATP) channels or the Na-K pump can be expected to influence the retinal blood flow.
Jeppesen
Peter
P
Dept of Ophthalmology, Arhus University Hospital, Arhus, Denmark. pj@dadlnet.dk
Aalkjaer
Christian
C
Bek
Toke
T
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D012161:Retinal Artery / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000502:physiology*; D013552:Swine; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D000241:Adenosine; D011188:Potassium; D005905:Glyburide