Etude, à l’aide de microinjections de 42K, de la perméabilité au potassium des segments corticaux du néphron

Abstract

Microinjections of solutions containing both K42 and C14 Inulin were performed into proximal and distal convoluted tubules as well as in cortical peritubular capillaries in rats undergoing a saline diuresis. Excretory patterns of these substances were analyzed in successive urine samples. C14 Inulin is entirely recovered in the urine of the experimental kidney after it was injected in proximal and distal tubules, and evenly distributed in urine coming from both kidneys after its introduction into the peritubular capillaries. The excretory patterns of radiopotassium are identical after its introduction into proximal convoluted tubules as well as into peritubular capillaries: its excretion is confined to the experimental kidney, it appears prior to simultaneously injected inulin, reaches a smooth maximum and its concentration is then exponentially decreasing with time. A large fraction of K42 injected into distal tubules is excreted along with C14 Inulin. The identity of excretory patterns of K42 following its injection either in proximal tubules or in peritubular capillaries, rules out a direct recovery of K42 when injected in proximal tubules, but suggests its passage through a cellular compartment, precursor or urinary potassium. The exponential decay of K42 in successive urine samples allows an estimation of the turnover rate of this pool. The high value obtained (30% min-1) points out the very high potassium permeability of tubular cells of renal cortex, and suggests that the renal potassium flow may act as a limiting factor.