BURG, MAURICE, AND NORDICA GREEN. Function of the thick ascending limb of Henle’s loop. Am. J. Physiol. 224(3) : 659-668. 1973.-The thick ascending limb of Henle’s loop was dissected from rabbit kidneys and perfused in vitro. There was net NaCl absorption from the tubule lumen with resultant lowering of lumen NaCl concentration below that of the bath. Since the electrical PD was positive in the lumen, Cl is absorbed actively. Na absorption is largely passive as indicated by comparison of 1) Na flux ratio and PD (at fast perfusion rates); and 2) Na concentration ratio and PD (at slow perfusion rates). However, the possibility of some active Na transport is not ruled out. The PD results from Cl transport. It is eliminated reversibly by removal of Cl from bath and lumen (SO4 substitution) and by ouabain. The PD is increased by removal of Na from bath and lumen (choline substitution). Na permeability is greater than Cl permeability, as indicated by I) the NaCl diffusion potential that is lumen positive when lumen NaCl concentration is low, and 2) radioisotope measurements of ion fluxes. Water permeability (Lp) is low, which combined with the NaCl transport accounts for the dilution of the urine in this segment.

Function of the thick ascending limb of Henle's loop.

The effect of prostaglandin E1 (PGE1) on the water permeability response to vasopressin, theophylline, and cyclic adenosine 3′,5′-monophosphate (C-AMP) of isolated, perfused collecting tubules of the rabbit was investigated in vitro Prostaglandin is a naturally occurring substance present in a number of tissues, including kidney It has been implicated in the action of a variety of hormones, many of which are known to exert their physiological effects through the intermediacy of the C-AMP system In the collecting tubule, PGE1 (10-7 M) elicited a minimal increase in net water absorption along an osmotic gradient However, when administered in association with a concentration of vasopressin (25 μU ml-1) selected to induce a submaximal increment in water absorption, the effect of the latter was reduced by approximately 50% Theophylline (5 × 10-3 M) also increased net water absorption, an effect not previously demonstrated in renal tissue This effect was potentiated by the simulataneous addition of PGE1 In contrast, PGE1 did not influence the increase in net water absorption induced by C-AMP (10-2 M) Since C-AMP is responsible for the permeability effects of vasopressin in renal tissue, the present results are consistent with the view that PGE1 interferes with the action of the octapeptide by competing with it at a site which influences the generation of C-AMP In addition it is proposed that prostaglandin may be an important modulator of the action of vasopressin The tubule is exquisitely sensitive to the hormone, responding to as little as 025 μU ml-1 It is conceivable that in the intact animal prostaglandin may serve to dampen the effects of small amounts of residual hormone and thereby prevent overshoots in permeability which might otherwise occur

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Effect of prostaglandin E1 on the permeability response of the isolated collecting tubule to vasopressin, adenosine 3′,5′-monophosphate, and theophylline

BURG, MI., L. STONER, J. CARDINAL, AND N. GREEN. Furosemide effect on isolated perfused tubules. Am. J. Physiol. 225(l): 119-124. 1973 .-Proximal convoluted tubules, thick ascending limbs of Henle’s loop, and cortical collecting tubules were dissected from rabbit kidneys, and perfused in vitro. The effect of the diuretic agent furosemide on electrolyte transport and electrical potential difference (PD) in these segments was determined. Furosemide in the lumen (lo-” to lOA M) inhibited active Cl transport in the thick ascending limbs of Henle’s loop with resultant decrease in net NaCl absorption and electrical PD. Concentrations of furosemide as high as 10 -4 M in the bath had little effect. Furosemide at low4 M also had no definite effect on proximal convoluted tubules and cortical collecting tubules whether placed in the bath and/or the lumen. We conclude that the principal renal action of this drug is to inhibit active Cl transport in the thick ascending limb of Henle’s loop.

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Furosemide effect on isolated perfused tubules.

https://www.amjmed.com/article/0002-9343(67)90093-9/pdf

The role of adenosine 3′,5′-phosphate in the action of antidiuretic hormone

The ubiquitous members of the aquaporin (AQP) family form transmembrane pores that are either exclusive for water (aquaporins) or are also permeable for other small neutral solutes such as glycerol (aquaglyceroporins). The purpose of this review is to provide an overview of our current knowledge of AQP structures and to describe the structural features that define the function of these membrane pores. The review will discuss the mechanisms governing water conduction, proton exclusion and substrate specificity, and how the pore permeability is regulated in different members of the AQP family.

The structure of aquaporins

GRANTHAM, JARED J., AND MAURICE B. BURG. Effect ofuasopressin and cyclic AMP on permeability of isolated collecting tubules. Am. J. Physiol. 21 I (I) : 255-259. rg66.-The effect of vasopressin and cyclic 3’,5’-AMP on the permeability to water and urea of the isolated perfused rabbit collecting tubule was measured. When added to the solution bathing the outside of the tubule, these agents regularly increased both net water absorption along an osmotic gradient and the diffusional permeability to water as measured with THO in the absence of an osmotic gradient. When added only to the solution bathing the luminal border of the cells, vasopressin was ineffective. Urea permeability was not significantly altered by either vasopressin or cyclic 3’) $-AMP despite simultaneous increases in water permeability.

JJ Grantham

Papers

Effect of vasopressin and cyclic AMP on permeability of isolated collecting tubules