Sodium and potassium transport in ferret red cells.

Abstract

SUMMARY1. Potassium movements into ferret red cells were measured with the tracer 86Rb. Equilibration of 86Rb between medium and cells could be resolved into two components. 70-90 % occurred rapidly with a rate constant of between 3-5-5-5 h-1. The remaining 10-30 % occurred slowly. The slow movement was equivalent to a potassium influx of about 1P2-2-76 mmol 1-1 cell h-1.2. Potassium influx was inhibited by 8-90% byO-mM-bumetanide (a high-ceiling, loop diuretic). This suggests that the sodium-potassium co-transport system has a high capacity for carrying potassium (estimated at about 17-35 mmol 1-1 cell h-1).3. After bumetanide (0-1 mM) remaining potassium movements (approximately 05 mmol 1-1 cell h-1) are at a similar level to that found in red cells from other animals.4. The sodium pump makes a very small contribution to potassium flux into ferret red cells. Much of this pump activity may be attributed to reticulocytes present in cell samples.5. Sodium movements across the red cell membrane were measured with 22Na.

The effects of calcium on potassium transport in ferret red cells.

“…It is not possible to simplify flux measurement by using quinine to inhibit the calciumactivated system since it also inhibits co-transport (Flatman, 1983), nor is it possible to wait for the calcium-activated system to spontaneously inactivate since the effects of calcium on the co-transport system are also time dependent. Fig.…”

“…This diuretic inhibits sodium-potassium-chloride cotransport in ferret red cells (Flatman, 1983;Hall & Ellory, 1985;Mercer & Hoffman, 1985). Half-maximal inhibition of potassium fluxes through the co-transport system was achieved with 2'2 x 10-7 M-bumetanide (data not shown).…”

“…Potassium influx was measured using tracer 42K or 86Rb according to the method described by Flatman, 1983. 42K activity was corrected for decay assuming a half-life of 12*36 h. When necessary, 86Rb activity was corrected for decay assuming a half-life of 18-7 days.…”

“…All fluxes were measured at 38°C in suspensions with haematocrits between 3 and 10 %. The haematocrits of suspensions or the extent of haemolysis were measured by the cyanmethaemoglobin method (see Flatman, 1983;Flatman & Andrews, 1983).…”

“…Sodium-potassium-chloride co-transport capacity in ferret red cells is very large (Flatman, 1983;Hall & Ellory, 1985;Mercer & Hoffman, 1985) and is much greater than the capacities of other cation transporters in this cell. Ferret red cells thus provide an excellent system in which to examine factors which might control the activity of the co-transport system.…”