The effects of flow on the transport of potassium ions through the walls of single perfused frog mesenteric capillaries

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Abstract
We have investigated the effects of varying flow velocity upon permeability to potassium ions (PK) of single perfused mesenteric microvessels in pithed frogs. P K was estimated using a development of the single bolus microperfusion technique at chosen flow velocities (U) in the range of 150–7000 μm s−1. In thirty‐seven out of forty‐three vessels, there was a strong positive correlation between PK and U. Average values (median) for PK (μm s−1) were related to U (μm s−1) by the expression: PK= 0.0043U+ 4.05 (n= 43). The correlation between PK and U was independent of microvascular pressure (and hence fluid filtration) over the range of 5–70 cmH2O. The correlation between PK and U was independent of the potassium concentration in the bolus over the range of 2–40 mmol l−1 and of the direction of the potassium flux through the capillary walls.