Single proximal tubules of Necturus kidney. VII: Ion fluxes across individual faces of cell

¹ Biophysical Laboratory, Harvard Medical School, Boston, Massachusetts

A method has been devised to calculate the fluxes across the individual faces of Necturus kidney proximal tubule cells. For this purpose data obtained from experiments using the stopped-flow microperfusion technique of measuring tracer disappearance from the tubular lumen are combined with data obtained in earlier experiments in which tracer uptake in Necturus kidney was measured. The combined data have been analyzed on an analogue computer on the assumption that the system may be described with three compartment kinetics (compartment 1, lumen; 2, proximal tubular cells; 3, extratubular space). For Na, the flux from compartment 1 to 2, '₁₂, = 308 pmoles/cm² sec, and the remaining fluxes in the same units are: '₂₁, 246; '₂₃, 132; '₃₂, 89. In the case of K, the fluxes are '₁₂ = '₂₁ = 57; '₂₃ = '₃₂ = 378. It has not been possible to obtain an analogue computer solution for the Cl fluxes in all cases. The interpretation of these calculated Na and K fluxes is discussed both in terms of the assumptions involved in the calculations, and in the application of the Ussing flux ratio for ion transport.