Juha P . Kokko

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This study was designed to examine whether prostaglandin E2 can directly affect sodium transport across isolated perfused rabbit renal collecting tubules. Changes in transepithelial potential and isotopic sodium fluxes in response to peritubular prostaglandin E2 were measured. In addition, changes in transepithelial potential of the outer medullary(More)
Transport of NaCl and water was examined in the rabbit medullary thick ascending limb of Henle (ALH) by perfusing isolated segments of these nephrons in vitro. Osmotic water permeability was evaluated by perfusing tubules against imposed osmotic gradients. In these experiments the net transport of fluid remained at zero when segments of thick ALH were(More)
Calcium and phosphate transport was examined in rabbit thin descending, thin ascending, and thick ascending limbs of Henle by in vitro perfusion of isolated tubular segments. Permeability coefficients for these segments with 45Ca and 32PO4 were determined for both lumen-to-bath and bath-to-lumen directions. Both the thin descending and thin ascending limbs(More)
Water homeostasis is regulated in large part by the proper operation of the urinary concentrating mechanism. In the renal inner medulla, urea recycling from the inner medullary collecting duct to the inner medullary interstitium is thought to be essential for the production of a concentrated urine; however, it has not been possible to test this hypothesis(More)
Studies were designed to examine whether the thin ascending limb of Henle (tALH) decreases its luminal solute concentration by an active or a passive transport process. In all experiments isolated segments of rabbit tALH were perfused in vitro. When tubules were perfused with solutions identical to the bath, active transport of NaCl was excluded by the(More)
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(More)
Our previous in vitro studies have disclosed that the thin ascending limb of Henle (tALH) possesses some unique membrane characteristics. In those studies we failed to demonstrated active transport of sodium chloride by the tALH, although it was shown that the isotopic permeability to sodium and chloride was unusually high. However, we did not examine the(More)
Until recently it has not been possible to compare directly the function of superficial and juxtamedullary nephrons. The present studies, using in vitro microperfusion, were designed to examine whether functional differences exist between proximal convoluted tubule segments of superficial and juxtamedullary nephrons. Electrophysiological studies showed that(More)
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(More)