THE EFFECTS OF FLOW ON THE TRANSPORT OF POTASSIUM-IONS THROUGH THE WALLS OF SINGLE PERFUSED FROG MESENTERIC CAPILLARIES

1. We have investigated the effects of varying flow velocity upon perm eability to potassium ions (P-K) of single perfused mesenteric microve ssels in pithed frogs. 2. P-K was estimated using a development of the single bolus microperfusion technique at chosen flow velocities (U) i n the range of 150-7000 mu m s(-1). 3. In thirty-seven out of forty-th ree vessels, there was a strong positive correlation between P-K and U . Average values (median) for P-K (mu m s(-1)) were related to U (mu m s(-1)) by the expression: P-K = 0.0043 U + 4.05 (n = 43). 4. The corr elation between P-K and U was independent of microvascular pressure (a nd hence fluid filtration) over the range of 5-70 cmH(2)O. 5. The corr elation between P-K and U was independent of the potassium concentrati on in the bolus over the range of 2-40 mmol l(-1) and of the direction of the potassium flux through the capillary walls.