The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone

Li, Jack H. Y.; Palmer, Lawrence G.; Edelman, Isidore S.; Lindemann, Bernd

doi:10.1007/bf01870770

Cited by 150 publications

(81 citation statements)

References 33 publications

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“…Our results in the CCT confirm the presence of saturation of the singlechannel conductance, although half saturation was at a somewhat higher concentration than that of the A6 cell channel (75 mM vs. 17-47 mM). This concentration is also higher than that required to half-saturate short-circuit current in amphibian epithelia (13,18,19) or net Na fluxes across the rabbit CCT (20). This discrepancy could result in part from a decrease in the driving force for Na or from a reduction in the number ofopen channels when external Na is increased in the transepithelial measurements.…”

Section: Discussionmentioning

confidence: 97%

“…The dependence of single-channel conductance on apical (pipet) Na is of interest because Na transport across many tight epithelia is a saturable function of apical Na with half saturation in the range of 10-30 mM (13,(18)(19)(20). Using fluctuation analysis, Van Driessche and Lindemann (21) found that single-channel currents in the frog skin did not saturate, but rather the number of conducting channels decreased with increasing apical Na.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Amiloride-sensitive Na channels from the apical membrane of the rat cortical collecting tubule.

Palmer¹,

Frindt²

1986

Proc. Natl. Acad. Sci. U.S.A.

264

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Currents through individual Na channels in the apical membrane of the rat cortical collecting tubule were resolved by using the patch-clamp technique. In cell-attached patches, the channels had a conductance of 5 pS with 140 mM NaCi in the pipet. The conductance was a saturable function of external Na, with a maximal value of about 8 pS and a half saturation at about 75 mM Na. In excised inside-out patches, the selectivity of the channels for Na over K was estimated from reversal potentials to be at least 10:1. The channels underwent spontaneous transitions between open and dosed states. Both states had mean lifetimes of 3-4 sec. Amiloride (0.5 pM) added to the pipet induced more frequent closures and openings of the channels and a reduction in the mean open time. These channels are presumed to mediate Na reabsorption by this nephron segment in vivo.According to the Koefoed-Johnsen-Ussing model of Nareabsorbing epithelia (1), Na enters the epithelial cell across the outer or apical border by diffusion through a membrane selectively permeable to Na. Measurements of current noise across these membranes indicate that this permeability is conferred by apical membrane Na channels (2). Here we report the use of the patch-clamp technique (3) to study single-channel activity in the apical membrane ofthe rat renal cortical collecting tubule (CCT). The channels exhibit many of the properties expected of them on the basis of transepithelial electrical and flux measurements in tight epithelia. These properties include the single-channel conductance, a high selectivity to Na, and block by luminal amiloride. METHODSSprague-Dawley rats of either sex (75-100 g) raised free of viral infections (Charles River Laboratories, Kingston, NY) were kept on a Na-deficient diet (ICN) with free access to tap water for 10-30 days. The animals were sacrificed by cervical dislocation, and one kidney was quickly removed. A CCT was dissected free under a microscope in oxygenated, bicarbonate-free Ringer's solution (pH 7.4) The open tubules were bathed at room temperature in a medium containing 135 mM NaCl, 5 mM KCl, 2 mM CaCl2, 1 mM MgCI2, 2 mM glucose, and 10 mM Hepes/NaOH at pH 7.3. Pipet solutions normally contained 140 mM NaCl, 3 mM MgCl2, and 10 mM Hepes/NaOH at pH 7.3. The Na concentration in the pipet was increased by adding NaCl and reduced by isosmotically replacing NaCl with N-methyl-Dglucamine hydrochloride. For measurements using insideout patches, the bath medium was replaced with either the normal pipet solution or one containing 47 mM NaCl, 93 mM KCl, 3 mM MgCl2, and 10 mM Hepes/KOH at pH 7.3. Patch-clamp techniques followed the methods of Hamill et al. (3). Pipets were pulled from blue-tip hematocrit glass (Fisher) in three stages with a modified vertical pipet puller (David Kopf, Tujunga, CA) and used uncoated. The pipets were mounted onto the headstage of a patch-clamp amplifier (Dagan Corp., Minneapolis, MN) and lowered gently onto the apical surface of the tubule. Seals were formed by applying suction to the pipet....

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Amiloride-sensitive Na channels from the apical membrane of the rat cortical collecting tubule.

Palmer¹,

Frindt²

1986

Proc. Natl. Acad. Sci. U.S.A.

264

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“…Alternatively, channels may be acquired from a pool of quiescent channels already present in the membrane (Li, Palmer, Edelman & Lindemann, 1982). In epithelial cells cytoskeletal proteins mediate important membrane functions.…”

Section: Discussionmentioning

confidence: 99%

Sodium‐dependent regulation of epithelial sodium channel densities in frog skin; a role for the cytoskeleton.

Chou

1993

The Journal of Physiology

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SUMMARY1. A weak electroneutral sodium channel blocker 6-chloro-3,5-diamino-pyrazine-2-carboxamide was used to perform noise analysis on isolated epithelium from Rana fuscigula to determine the cellular mechanism underlying autoregulation of Na+ channel densities in response to a reduction in the mucosal Na+ concentration.2. The inherent transport rates of these tissues were generally lower than in other frog skins. and to a lesser extent by an increase in NT, the total number of open and closed channels. 5. We also examined the role of the cytoskeleton in the regulation of Na+ channel densities. Colchicine treatment, which disrupted microtubules, had no apparent effect on the ability of the tissues to autoregulate their Na+ channel densities.6. The integrity of the microfilaments were essential for autoregulatory changes in No. After we had disrupted the microfilaments with cytochalasin B, we observed a marked reduction in the ability of the tissues to increase N0. 7. The mean No did not increase in response to a drop in mucosal Na+ despite the fact that /3' increased by 69 %. We, therefore, assumed that cytochalasin B did not affect Na+ channels already present in the membrane but interfered with recruitment of new channels. Significantly, we did not observe any increase in NT. 8. In kidney and other tight epithelia, microfilaments are responsible for regulating the delivery of newly synthesized membrane proteins. We believe that our results with cytochalasin-treated tissues support the theory that autoregulatory changes in N0 are also regulated by the recruitment of channels from a cytoplasmic pool.

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“…For example, vasopressin increases sodium transport in frog skin and toad urinary bladder via cyclic AMP as suggested first by Orloff & Handler (1967). Recent work has shown that vasopressin recruits electrically silent channels without affecting the mean life-time or unit conductance of individual channels (Li, Palmer, Edelman & Lindemann, 1981). In this way the recruitment of silent channels accounts for the macroscopic increase in sodium SCC.…”

Section: Introductionmentioning

confidence: 86%

Conversion of sodium channels to a form sensitive to cyclic AMP by component(s) from red cells

Cuthbert

Spayne

1983

British J Pharmacology

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1Sodium transport has been measured in the isolated epithelium from colons of male SpragueDawley rats. 2 Sodium transport in colons was induced by pretreating the animals with dexamethasone (6 mg kg-) which caused the appearance of an amiloride-sensitive short circuit current within a few hours. 3 Forskolin, a diterpene, which activates adenylate cyclase, was found to increase the cyclic adenosine monophosphate (cyclic AMP) content of rat colons and also to increase short circuit current at the same time. However, measurements of chloride and sodium fluxes across the epithelium indicated that forskolin activates chloride secretion but has no effect on sodium transport.4 In confirmation of (3) it was found that the amiloride-sensitive short circuit current was unchanged after the short circuit current had been increased by forskolin under a variety of conditions. 5The behaviour of the mammalian colon as indicated in (3) and (4) is unlike that of amphibian sodium transporting epithelia. It is shown that in toad urinary bladder forskolin increases amiloridesensitive short circuit current. 6 Procedures were investigated which might make sodium transport in the mammalian colon sensitive to cyclic AMP. Exposing the apical surface to sonicated suspensions of nucleated red cells (frog, toad and duck), followed by washing, gave preparations with amiloride-sensitive short circuit currents which were increased by forskolin or dibutyryl cyclic AMP. 7 It would appear that the sodium channel in the mammalian colon, unlike that of amphibian tissues, has lost the ability to have its properties modified by cyclic AMP. Incubation of colons with sonicated suspensions of nucleated red cells apparently modifies the tissues such that sodium transport across the tissue becomes sensitive to the nucleotide.

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The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone

Cited by 150 publications

References 33 publications

Amiloride-sensitive Na channels from the apical membrane of the rat cortical collecting tubule.

Amiloride-sensitive Na channels from the apical membrane of the rat cortical collecting tubule.

Sodium‐dependent regulation of epithelial sodium channel densities in frog skin; a role for the cytoskeleton.

Conversion of sodium channels to a form sensitive to cyclic AMP by component(s) from red cells

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