Cell membrane water permeabilities and streaming currents in Ambystoma proximal tubule

An electrophysiological approach is used to analyze the possible routes of osmotically driven water flow across the isolated perfused Ambystoma proximal tubule. The minimum hydraulic conductivities (Lp) of the cell membranes were estimated from the initial rate of change of intracellular activities of Na+ and K+ in response to a step gradient of 50 or 100 mosmol/kg sucrose. The Lp of the apical membrane is 1.30 X 10(-4) cm.s-1.osM-1 referred to the luminal epithelial surface and 2.45 X 10(-6) cm.s-1.osM-1 when corrected for amplification of the brush border (n = 8). The Lp of the basolateral membrane is 1.42 X 10(-4) cm.s-1.osM-1 referred to the basement membrane surface and 6.39 X 10(-6) cm.s-1.osM-1 when corrected for the amplification of the basal and lateral membranes (n = 5). Transepithelial water flows were generated in either direction by a unilateral step increase of osmolality with 100 mosmol sucrose. Bath-to-lumen flow increased paracellular transepithelial resistance (R3) by 48%; lumen-to-bath flow decreased R3 by only 3%. A bilateral increase in the osmolality of both solutions by 50 mosM had no significant effect on R3. Streaming potentials were observed during trans-epithelial water flow induced by unilateral gradients of sucrose; their polarity, magnitude, site of generation, and insensitivity to change of paracellular resistance are all indicative of water flow through paracellular structures, especially the lateral intercellular spaces. Contrary to earlier suggestions (J. M. Diamond, J. Membr. Biol. 51: 195-216, 1979), these potentials are not primarily diffusion potentials across anion-selective tight junctions resulting from solute polarization in the unstirred layers. Instead, a true electrokinetic basis for these streaming potentials is indicated by their continued presence after deletion of all Cl-. Thus water moves through both cellular and paracellular pathways in this epithelium.

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A network thermodynamic model of salt and water flow across the kidney proximal tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1978.235.6.f638 ◽

1978 ◽

Vol 235 (6) ◽

pp. F638-F648 ◽

Cited By ~ 2

Author(s):

S. R. Thomas ◽

D. C. Mikulecky

Keyword(s):

Proximal Tubule ◽

Water Flow ◽

Thermodynamic Model ◽

Circuit Simulation ◽

Basolateral Membrane ◽

Kidney Proximal Tubule ◽

Network Analyses ◽

Pump Rate ◽

Parameter Values ◽

The Given

This network thermodynamic model of kidney proximal tubule epithelium treats coupled salt and water flow across each component membrane of the epithelium. We investigate the effects of various relative internal parameter values on the concentration of transepithelial flow, the concentrations in the cell and interspace, and the distribution of flows between cellular and paracellular routes. Best fit is obtaine if the apical and basolateral membrane reflection coefficients (or) are equal. The measured transepithelial filtration coefficient, Lp, is a function not only of the component Lps but also of the internal concentrations, or's, and permeabilities. For the given system topology (i.e., connectedness), parameters of component membranes must be within a narrow range to be consistent with experimental results. The dependence of the concentration of transported fluid on the balance between the solute pump rate and the transepithelial volume flow driving force is shown. This has implications for the effects of peritubular or lumen oncotic pressure on salt and water flow. With Appendix B of this paper and a user's guide for a circuit-simulation package (e.g., SPICE or PCAP) the reader can perform similar network analyses of transport models himself.

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Effect of norepinephrine on intracellular pH in kidney proximal tubule: role of Na+-( HCO 3 − ) n cotransport

AJP Renal Physiology ◽

10.1152/ajprenal.1998.275.1.f33 ◽

1998 ◽

Vol 275 (1) ◽

pp. F33-F45 ◽

Cited By ~ 2

Author(s):

Solange Abdulnour-Nakhoul ◽

Raja N. Khuri ◽

Nazih L. Nakhoul

Keyword(s):

Membrane Potential ◽

Proximal Tubule ◽

Intracellular Ph ◽

Basolateral Membrane ◽

Inhibitory Effect ◽

Rate Of Change ◽

Kidney Proximal Tubule ◽

Luminal Membrane ◽

Basolateral Membrane Potential

We examined the effect of norepinephrine (NE) on intracellular pH (pHi) and activity of Na+([Formula: see text]) in the isolated perfused kidney proximal tubule of Ambystoma, using single-barreled voltage and ion-selective microelectrodes. In control[Formula: see text] Ringer, addition of 10−6 M NE to the bath reversibly depolarized the basolateral membrane potential ( V 1), the luminal membrane potential ( V 2), and the transepithelial potential difference ( V 3) and increased pHi by 0.14 ± 0.02. These effects were mimicked by isoproterenol but were abolished after pretreatment with SITS or in the absence of CO2/[Formula: see text]. Removal of bath Na+ depolarized V 1 and V 2, hyperpolarized V 3, and decreased pHi. These effects are largely mediated by the electrogenic Na+-([Formula: see text]) n cotransporter. In the presence of NE, the effects of Na+ removal on membrane potential differences and the rate of change of pHi were significantly smaller. Reducing bath [Formula: see text] concentration from 10 to 2 mM at constant CO2 (pH 6.8) depolarized V 1 and V 2, decreased pHi, and lowered[Formula: see text]. These changes are also due to Na+-([Formula: see text]) n . In the presence of NE, reducing bath [[Formula: see text]] caused a smaller depolarizations of V 1 and V 2, and the rate of pHi decrease was significantly reduced. Our results indicate: 1) NE causes an increase in pHi; 2) the NE-induced alkalinization is mediated by a SITS-sensitive and[Formula: see text]-dependent transporter on the basolateral membrane; and 3) in the presence of NE, the reduced effects caused by basolateral[Formula: see text] changes or Na+ removal are indicative of an inhibitory effect of NE on Na+-([Formula: see text]) n cotransport.

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A model of NaCl and water flow through paracellular pathways of renal proximal tubules

The Journal of Membrane Biology ◽

10.1007/bf01870256 ◽

1975 ◽

Vol 23 (1) ◽

pp. 305-347 ◽

Cited By ~ 24

Author(s):

Ronald E. Huss ◽

Donald J. Marsh

Keyword(s):

Water Flow ◽

Proximal Tubules ◽

Renal Proximal Tubules ◽

Flow Through ◽

Paracellular Pathways

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Axial heterogeneity of rabbit proximal tubule luminal H+ and basolateral HCO3- transport

AJP Renal Physiology ◽

10.1152/ajprenal.1989.256.2.f335 ◽

1989 ◽

Vol 256 (2) ◽

pp. F335-F341

Author(s):

M. Baum

Keyword(s):

Proximal Tubule ◽

Intracellular Ph ◽

Basolateral Membrane ◽

Sodium Concentration ◽

Rate Of Change ◽

Bathing Solution ◽

Proton Secretion ◽

Sodium Dependent ◽

Convoluted Tubules

The present in vitro microperfusion study examined whether the rates of the apical membrane Na+-H+ antiporter and basolateral membrane Na(HCO3)3 symporter vary along the length of the proximal tubule. Initial proximal convoluted tubules (PCT obtained within 0.5 mm from the glomerulus), mid-PCT (PCT without glomerular attachments) and cortical proximal straight tubules were examined. The rate of either the apical or basolateral membrane acidification mechanism was measured from the initial rate of change of intracellular pH after a change in either the luminal or bathing solution. Intracellular pH was measured fluorometrically using the pH-sensitive dye (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. The rate of bicarbonate exit across the basolateral membrane was examined by imposing either a sodium or bicarbonate gradient. There was no difference between initial and mid-PCT, but the rate of change in cell pH was 30% slower in PST in both series. The rate of sodium-dependent apical proton secretion was examined by changing the sodium concentration in the lumen. There was no difference in sodium-dependent apical proton secretion in initial vs. mid-PCT, but the rate fell by 70% in the proximal straight tubule (PST). These differences were not due to a difference in buffer capacity in these segments. These data are consistent with a homogeneous rate of apical Na+-H+ antiporter and basolateral Na(HCO3)3 activity along the rabbit PCT, but a lower rate in the PST.

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Video measurement of basolateral membrane hydraulic conductivity in the proximal tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1983.245.1.f123 ◽

1983 ◽

Vol 245 (1) ◽

pp. F123-F129 ◽

Cited By ~ 3

Author(s):

L. W. Welling ◽

D. J. Welling ◽

T. J. Ochs

Keyword(s):

Proximal Tubule ◽

Cell Membranes ◽

Driving Forces ◽

Membrane Surface ◽

Basolateral Membrane ◽

Apical Cell ◽

Water Flux ◽

Surface Areas ◽

Video Recordings ◽

Proximal Tubule Segments

Isolated, lumen-collapsed S1, S2, and S3 proximal tubule segments from the rabbit were exposed acutely to media made hypotonic or hypertonic by adjusting the concentration of the impermeant solute raffinose. The result was a water flux into or out of the cells across their basolateral cell membranes and a consequent swelling or shrinking of the cells. From tubule volume changes measured at 1/60-s intervals during the first 0.03-0.2 s of video recordings, the earliest water fluxes were found to be 0.76 +/- 0.04 nl X min-1 X mm-1 X mosM-1 in S1, 0.53 +/- 0.03 in S2, and 0.35 +/- 0.04 in S3. When normalized to outer tubule surface areas, these fluxes yield statistically different hydraulic conductivities of about 5,500, 4,000, and 3,000 microns X s-1 in the three segments. However, when normalized to the basolateral membrane surface areas, the basolateral membrane hydraulic conductivities are all approximately 300 microns X s-1 and not statistically different. If one assumes that the hydraulic conductivities of the basolateral and apical cell membranes are equal, the latter value agrees with reported transtubular measurements and is sufficient to allow nearly isotonic transcellular absorption to occur with driving forces of 2-3 mosM.

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Correlation of structure and function in developing proximal tubule of guinea pig

AJP Renal Physiology ◽

10.1152/ajprenal.1989.256.1.f13 ◽

1989 ◽

Vol 256 (1) ◽

pp. F13-F17 ◽

Cited By ~ 1

Author(s):

L. W. Welling ◽

A. P. Evan ◽

V. H. Gattone ◽

S. Rollins ◽

R. Saunders ◽

...

Keyword(s):

Guinea Pig ◽

Proximal Tubule ◽

Membrane Surface ◽

Basolateral Membrane ◽

Postnatal Period ◽

Adult Rabbit ◽

Adult Rat ◽

Surface Areas ◽

Length Data ◽

And Function

Unlike the case in rat, rabbit, and other species in which nephron formation continues into the newborn period, nephrogenesis in the guinea pig is completed well before the time of birth. Therefore, the marked increase in proximal tubule reabsorption that occurs during the postnatal period in that species can be attributed entirely to an increase in the absorptive capacity of existing nephron units. The purpose of the present morphometric studies was to correlate that change in proximal tubule function with changes in the apical and basolateral cell membrane surface areas. The apical and basolateral membrane surface densities were found to be approximately equal to each other and to remain constant throughout development. Because of increasing tubule volume, however, both membranes doubled in size between 1 and 3 wk of age and eventually increased by a factor of 3.5 in the adult. At the same time, there was little change in the length of tight function complexes measured in the plane of the luminal surface. Using previously published functional data and tubule length data, a good correlation was found between absolute absorption and total basolateral membrane surface area throughout the entire period of development in proximal tubules. Absorption per unit area of basolateral membrane was approximately 0.55, 0.41, 0.56, and 0.42 X 10(-6) nl.min-1.micron-2 in the 1st, 2nd, and 3rd wk, and in adult animals, respectively, and thus was similar to that reported for proximal tubule segments of adult rabbit and juvenile to adult rat.

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