1. We have investigated the effects of varying flow velocity (U) upon permeability to potassium ions (P(K)) of single perfused mesenteric venules in anaesthetised rats. P(K) was estimated using a development of the single bolus microperfusion technique at chosen flow velocities in the range of 300 to 6000 μm s-1. 2. In an initial study on 12 vessels, there was a strong positive correlation between P(K) and U. This was described by the relation: P(K) = 0.0053U + 8.86, where P(K) and U are both expressed in micrometres per second (μm s-1). The addition of the nitric oxide (NO) synthase inhibitors (20 μmol l-1) N(G)-monomethyl-L-arginine (L-NMMA) and N(G)-nitro L-arginine (L-NNA) to the superfusate abolished the positive correlation between P(K) and U. The addition of D-NNA (20 μmol l-1) did not change the relation between P(K) and U where the median value for the slope of the relation was 57.7 (± 58.7 interquartile (IQR)) x 10-4 (n = 4). The addition of L-arginine (200 μmol l-1) restored the relation between P(K) and U where the slope of the relation was increased from 3.9 (± 16.3 IQR) x 10-4 to 69.2 (± 13.5 IQR) x 10-4 (n = 7). 4. The addition of the guanylate cyclase inhibitor LY83583 (10 μmol l-1) abolished the positive correlation between P(K) and U (n = 6). 5. Our data suggest that the flow modulates the potassium permeability through the walls of single perfused rat mesenteric venules via a NO-cGMP-dependent process.
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