Pressure-induced myogenic responses in isolated bovine retinal arteries.
OBJECTIVE
To investigate whether a pressure-induced myogenic vasoconstriction can be demonstrated in isolated bovine retinal arteries and to determine the cellular mechanisms involved.


METHODS
Isolated bovine retinal arteries were mounted on a pressure myograph without flow and exposed to stepwise increases in intraluminal pressure. Changes in internal diameter were monitored continuously using an inverted microscope video system.


RESULTS
Bovine retinal arteries showed myogenic tone at pressures higher than 10 mm Hg. This pressure-induced contraction was absent in calcium-free Krebs-Ringer bicarbonate solution. Inhibition of L-type voltage-operated calcium channels with nifedipine (1 microM) suppressed the myogenic contraction. After depolarization of the vascular smooth muscle cells with a K+ 120 mM solution, a pressure-induced contraction was still observed, indicating that besides stimulation of voltage-operated calcium channels, depolarization-independent mechanisms contribute to the pressure-induced myogenic vasoconstriction.


CONCLUSIONS
Isolated bovine retinal arteries spontaneously contract when exposed to raised intraluminal pressure. This response depends on extracellular calcium and is blocked by nifedipine. In addition, depolarization-independent mechanisms seem to be involved.
Delaey
C
C
Department of Physiology and Pathophysiology, Ghent University, Belgium.
Van de Voorde
J
J
D000818:Animals; D001794:Blood Pressure; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002417:Cattle; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009213:Myography; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012161:Retinal Artery / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D015220:Calcium Channels; D014665:Vasodilator Agents; D009543:Nifedipine; D011188:Potassium; D002118:Calcium