MEASUREMENT OF HYDRAULIC CONDUCTIVITY IN ISOLATED ARTERIOLES OF RAT-BRAIN CORTEX

We have developed a new method for quantification of arteriolar hydrau lic conductivity (L(p)) from isolated rat brain vessels. The volume fl ux of water per unit surface area across the arteriole wall (J(v)/S) w as assessed from measurements of silicon oil drop movement within an o ccluded 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 an d applied pressure. L(p) was measured in isolated cerebral arterioles 1) at room temperature (22-degrees-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-degrees-C with vessels dilated submaximally wit h 10(-4) M adenosine (n = 6). L(p) at 22-degrees-C without adenosine w as 13.2 +/- 4.2 x 10(-9) (+/-SE) cm.s-1.cmH2O-1 for all vessels studie d. 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 sign ificantly (on average, 2.6-fold) with adenosine at 37-degrees-C but no t with adenosine at 22-degrees-C. Control L(p) bore no relationship to either the development of spontaneous tone or the diameter response t o pH change, two recognized indicators of vessel viability.