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D W Seldin

Publications and source records attributed to D W Seldin.

At least 73 records · Page 4Linked to original sources
PubMed1975

Transepithelial potential difference profile of the distal tubule of the rat kidney.

In a recent micropuncture study electrodes with relatively large tips (3 to 5 mu O.D.) and, hence, low tip resistances were used to measure the transepithelial potential difference (PD) across the proximal tubule of the rat kidney. The present study reexamines the PD of the distal tubule of the rat kidney using such electrodes. In contrast to previous studies where a negative PD has been uniformly found in the distal tubule, the transtubular PD was found to be positively oriented (+3.7 mv) when particular efforts were made to puncture the earliest accessible segments. In accord with previous observations, the PD of the late segment was consistently negative (mean, -19.6 mv). Morphologic examination of the epithelium at the site of puncture suggests that in the very early distal tubule where positive potentials are recorded, the epithelium is characteristic of the distal convoluted tubule. By contrast, in the latter part of the distal tubule, where negative potentials are recorded, the epithelium displays the morphologic characteristics of the cortical collecting duct. The results of these studies suggest that the net transport properties of the distal tubule, that is the region of the nephron beginning just beyond the macula densa and extending to the first junction with another renal tubule, are a composite of activities of at least two types of epithelium.

Animals↗
PubMed1975

Characteristics of salt and water transport in superficial and juxtamedullary straight segments of proximal tubules.

The purpose of the present studies was to characterize the nature of salt and water transport out of the superficial (SF) and juxtamedullary (JM) straight segments of rabbit proximal tubules as examined by in vitro microperfusion techniques. When the perfusate consisted of a solution simulating ultrafiltrate of plasma, there were no differences between SF and JM straight tubules in either net reabsorption of fluid (SF=0.47 nl/mm per min; JM=0.56 nl/mm per min) or in transtubular potential difference (PD) (SF=-2.1 mV; JM=-1.8 mV). Removal of glucose and alanine from the perfusate had no effect on the magnitude of the PD in either straight segment. Ouabain decreased both the net reabsorptive rates and the PD. Isosmolal replacement of NaCL by Na-cyclamate (a presumed impermeant anion) in the perfusate and the bath caused an increase in luminal negativity in both segments wheras similar substitution of NaCL by choline-CL (nontransported cation) changed the PD TO NEAR ZERO. These studies, therefore, suggest that sodium is transported out of the proximal straight tubules by an active noncoupled process that generates a PD (electrogenic process). When the perfusate consisted of a solution with a high chloride concentration (resulting from greater HCO3 than CI reabsorption in the proximal convoluted tubule), different PDs in SF and JM tubules were generated: SF=+1.6 plus or minus 0.2 mV; JM=-1.3 plus or minus 0.3 mV. This difference in PD was attributed to relative differences in Na and CI permeabilities in these two segments. Electrophysiological and isotopic estimates of the chloride to sodium permeability revealed that the SF tubule is about twice as permeant to chloride than to sodium whereas the JM tubules are approximately twice as permeant to sodium than to chloride. It is concluded that the mechanism of active sodium transport in the straight segment of proximal tubule differs from that of the convoluted segment and that both the SF and JM straight segments differ from each other with respect os sodium and chloride permeability.

Animals↗
PubMed1975

Evidence against bicarbonate reabsorption in the ascending limb, particularly as disclosed by free-water clearance studies.

Bicarbonate reabsorption in the thick ascending limb of Henle's loop was examined by studies of free-water clearance (CH2O) and free-water reabsorption (TcH2O). During maximal water diuresis in the dog, CH2O/GFR was taken as an indes of sodium reabsorption in, and urine flow (V/GFR) as an index of delivery of filtrate to, this scarbonate, infusion of a nonreabsorbable solute (hypotonic mannitol) and administration of an inhibitor of bicarbonate reabsorption (acetaent, but less than that achieved with hypotonic saline infusion. This suggests that sodium that sodium bicarbonate is not reabsorbed in the ascending limb. Rather, it is the sodium chloride, swept out of the proximal tubule by osmotic diuresis due to nonreabsorbed mannitol or sodium bicarbonate, that is reabsorbed in the ascending limb thereby increasing CH2O, whereas the nonreabsorption of mannitol and sodium bicarbonate results in a depressed CH20 per unit V when compared with hypotonic saline. V/GFR is not a satisfactory index of delivery to the ascending limb during osmotic diuresis, since it includes water obligated by nonreabsorbable solutes. When a better index of delivery, the sum of the clearances of chloride (CC1) and free-water (CH2O) is used, hypotonic bicarbonate infusion, hypotonic mannitol infusion and acetazolamide administration increase CH2O/GFR per unit delivery to the same extent as odes hypotonic saline infusion. Studies in dogs and rats on TcH2O also indicate that sodium bicarbonate is an impermeant solute in the ascending limb. Osmotic diuresis due to sodium bicarbonate diuresis, produced either by inhibition of sodium bicarbonate reabsorption (acetazolamide, L-lysine mono-hydrochloride) or infusion of sodium bicarbonate, or mannitol diuresis both produced marked chloruresis and increased TcH2O to the same extent as did hypertonic saline infusion. If chloride excretion was almost eliminated by hemodialysis against a chloride-free dialysate (dogs) or prolonged feeding of a salt-free diet (rats), TcH2O formation was unimpaired if hypertonic saline was infused but virtually obliterated during mannitol or sodium bicarbonate diuresis. Sodium reabsorption in the ascending limb, therefore, appears to be dependent upon chloride as the accompanying anion. At any given rate of bicarbonate excretion, more cloride is delivered out of the proximal tubule (as estimated from CC1 + CH2O) with hypotonic sodium bicarbonate infusion than with acetazolamide administration. This suggests that magnitude of the chlorutesis accompanying bicarbonate diuresis depends, not only on osmotic diuresis due to nonreabsorbed sodium bicarbonate, but also on the extent to which concomitant changes in effective extracellular volume influence overall sodium chloride reabsorption.

Acetazolamide↗
PubMed1974

Factors governing the transepithelial potential difference across the proximal tubule of the rat kidney.

Previous measurements of the transepithelial potential difference (PD) of the proximal tubule have yielded widely conflicting values (range -20 to +3 mV). In a recent study, Kokko has demonstrated that the PD of the in vitro perfused isolated proximal tubule of the rabbit varies in a predictable way from -6 to +3 mV, depending on the concentration of chloride, bicarbonate, glucose, and amino acids in the perfusing solution. The present micropuncture study examines the effect of tubular fluid composition on the PD profile along the proximal tubule of the in vivo rat kidney. Low resistance measuring electrodes with large tips (3-5 microns OD) filled with 3 M KCl, were used to provide stable PD recordings. Experiments were performed to validate the use of these electrodes. Transepithelial PD measurements were made in immediate postglomerular segments identified by injection of dye into Bowman's space of accessible surface glomeruli and in randomly selected more distal segments of the proximal tubule. In the control state, the first loop was found to have a small but consistently negative PD which could be obliterated by an infusion of phloridzin. In contrast, the PD in later segments was consistently positive. Infusion of acetazolamide abolished the positive PD in the later segments. Acetazolamide and glucose infusion resulted in a negative PD which was abolished by the additional infusion of phloridzin. These data provide evidence that glucose reabsorption is electrogenic and can account for the small negative PD normally present in the early proximal tubule. The positive PD in later segments appears to be a passive chloride diffusion potential. This positive potential is discussed as an important electrochemical driving force for significant passive reabsorption of sodium in the proximal tubule.

Acetazolamide↗