GFR regulation and flow-dependent electrophysiology of early distal tubule in Amphiuma

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Abstract
Tubuloglomerular feedback (TGF) in mammals and amphibians senses flow-dependent concentration changes in tubular fluid of the distal tubule and signals to arterioles to initiate changes in glomerular filtraction rate. The distal tubules and afferent arterioles are situated on the surface of the kidney of Amphiuma means. Micropuncture techniques were used to measure luminal nd intracellular chloride concentrations and the associated electrical potential differences, while tubular perfusion rate was varied. Transepithelial potential difference (PDte) and basolateral potential difference (PDbl) became more positive at increased tubular flow rates. Intratubular and intracellular chloride concentrations also increased significantly with perfusion rate. Single-nephron glomerular filtration rate decreased when perfusion rate was increased but this response was eliminated by the inclusion of furosemide in the perfusion solution; the drug also inhibited the flow dependence of PDte. The results suggest that local changes in PD and Cl- activity result from flow-dependent changes in the rate of hypertonic NaCl transport propagated along the length of the perfused segment; they establish a correlation between the rate of transport and the magnitude of the TGF inhibition; and, because transport and TGF can be jointly inhibited, they suggest a causal link between the two.

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