Measurement of hydraulic conductivity in isolated arterioles of rat brain cortex

We have developed a new method for quantification of arteriolar hydraulic conductivity (L(p)) from isolated rat brain vessels. The volume flux of water per unit surface area across the arteriole wall (J(v)/S) was assessed from measurements of silicon oil drop movement within an occluded vessel at two to three pressures (between 20 and 70 mmHg); the L(p) was derived from the slope of the relationship between J(v)/S and applied pressure. L(p) was measured in isolated cerebral arterioles 1) at room temperature (22°C) without spontaneous vessel tone (control L(p); n = 11), 2) at room temperature with 10^-4 M adenosine (n = 5), and 3) at 37°C with vessels dilated submaximally with 10^-4 M adenosine (n = 6). L(p) at 22°C without adenosine was 13.2 ± 4.2 x 10^-9 (±SE) cm · s^-1 · cmH₂O^-1 for all vessels studied. L(p) values ranged from 1.2 to 44.1 x 10^-9 cm · s^-1 · cmH₂O^-1 with a median value that was 5.9 x 10^-9 cm · s^-1 · cmH₂O^-1. L(p) increased significantly (on average, 2.6-fold) with adenosine at 37°C but not with adenosine at 22°C. Control L(p) bore no relationship to either the development of spontaneous tone or the diameter response to pH change, two recognized indicators of vessel viability.