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

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Abstract
1 We have investigated the effects of varying flow velocity (U) upon permeability to potassium ions (PK) of single perfused mesenteric venules in anaesthetised rats. PK 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 PK and U.This was described by the relation: PK= 0·0053U+ 8·86, where PK and Uare both expressed in micrometres per second (μm s−1). 3 The addition of the nitric oxide (NO) synthase inhibitors (20 μmol l−1) NG-monomethyl-L-arginine (L-NMMA) and NG-nitro L-arginine (L-NNA) to the superfusate abolished the positive correlation between PK and U.The addition of D-NNA (20 μmol l−1) did not change the relation between PK and Uwhere the median value for the slope of the relation was 57·7 (± 58·7 interquartile (IQR)) × 10−4 (n= 4). The addition of L-arginine (200 μmol l−1) restored the relation between PK and Uwhere the slope of the relation was increased from 3·9 (± 16·3 IQR) × 10−4 to 69·2 (± 13·5 IQR) × 10−4 (n= 7). 4 The addition of the guanylate cyclase inhibitor LY83583 (10 μmol l−1) abolished the positive correlation between PK 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.