Pressure-induced myogenic responses in isolated bovine retinal arteries

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.