Flow modulates the transport of K⁺ through the walls of single perfused mesenteric venules in anaesthetised rats

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.