Myogenic response in isolated porcine retinal arterioles.
OBJECTIVE
To study the myogenic response in large and small porcine retinal arterioles and the effects of blockade of L-type voltage gated calcium channels on the myogenic response.


METHODS
Eleven large (outer diameter 137.7 +/- 4.5 micro m) and fourteen small (77.3 +/- 3.7 micro m) isolated porcine retinal arterioles were studied for myogenic response while mounted between two double-barrelled pipette systems. The intraluminal pressure was varied from 0 to 140 cm H( 2)O (0-103 mmHg) and the diameter changes of the arterioles were registered. The pressure-diameter relation was determined for arterioles in calcium-containing and calcium free solutions and during inhibition of the L-type voltage gated calcium channels with nifedipine.


RESULTS
Both large and small retinal arterioles showed a decrease in diameter as the intraluminal pressure was increased, but no significant difference was found between large and small arterioles (p = 0.39). Blockade of voltage gated calcium channels significantly abolished the myogenic response (p = 0.010 and p = 0.005, large and small arterioles respectively).


CONCLUSIONS
The results indicate that myogenic responses are present throughout the retinal arteriolar system and that L-type voltage gated calcium channels are involved in transforming the stretch of retinal vascular smooth muscle cells induced by an increase in intraluminal pressure into a contraction.
Jeppesen
Peter
P
Department of Ophthalmology, Arhus University Hospital, Denmark. pj@dadlnet.dk
Aalkjaer
Christian
C
Bek
Toke
T
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D066298:In Vitro Techniques; D009543:Nifedipine / Q000494:pharmacology; D011312:Pressure; D012018:Reflex / Q000502:physiology*; D012171:Retinal Vessels / Q000187:drug effects / Q000502:physiology*; D013552:Swine; D014661:Vasoconstriction / Q000502:physiology*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D009543:Nifedipine; D002118:Calcium