PURPOSE. To investigate whether a pressure-induced myogenic vasoconstrictio
n 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 myogra
ph 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 t
han 10 mm Hg. This pressure-induced contraction was absent in calcium-free
Krebs-Ringer bicarbonate solution. Ambition of L-type voltage-operated calc
ium channels with nifedipine (1 mu M) suppressed the myogenic contraction.
After depolarization of the vascular smooth muscle cells with a K+ 120 mM s
olution, a pressure-induced contraction was still observed, indicating that
besides stimulation of voltage-operated calcium channels, depolarization-i
ndependent mechanisms contribute to the pressure-induced myogenic vasoconst
riction.
CONCLUSIONS. Isolated bovine retinal arteries spontaneously contract when e
xposed to raised intraluminal pressure. This response depends on extracellu
lar calcium and is blocked by nifedipine. In addition, depolarization-indep
endent mechanisms seem to be involved.