1. We have investigated the effects of various potential inhibitors on flow-dependent K+ permeability (P(K)) of single perfused mesenteric microvessels in pithed frogs. 2. Neither superfusion with a nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (10 or 100 μmol l-1), nor the addition of indomethacin (30 μmol l-1) to both perfusate and superfusate reduced the positive correlation between P(K) and flow velocity (U). 3. In the presence of agents known to raise intracellular levels of adenosine 3',5'-cyclic monophosphate (noradrenaline, 8-bromo-cAMP and a combination of forskolin and rolipram) the slope of the relation between P(K) and U was no longer significant, so that P(K) was no longer flow dependent. 4. These results confirm that the flow dependence of P(K) is a biological process and not an artefact of measurement and suggest a role for intracellular cAMP rather than nitric oxide or prostacyclin in the flow-dependent modulation of P(K) in frog mesenteric microvessels.
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