Single-cell electrical measurements and spectrophotometric determinations of intracellular pH were used to determine unique features of alpha- and beta-intercalated cells (alpha-IC, beta-IC) in in vitro perfused rabbit cortical collecting ducts (CCD). pHi rose in alpha-IC and fell in beta-IC after bath Cl- removal. Luminal Cl- removal did not change pHi of alpha-IC, but pHi of beta-IC rose by 0.36 +/- 0.01 pH units. Cl- concentration-dependent recovery of beta-IC pHi revealed a Cl- Km of 18.7 mM for the luminal Cl(-) -HCO3- exchanger. Measurements of basolateral membrane voltage (Vbl) also showed two IC cell types. Removal of luminal Cl- did not change Vbl in alpha-IC, whereas Vbl hyperpolarized by a mean of 73.2 +/- 3.5 mV in beta-IC. Reducing bath Cl- depolarized both alpha- and beta-IC Vbl. In alpha-IC a large repolarization of 39.8 +/- 5.2 mV followed acute depolarization after bath Cl- removal. Reducing bath HCO3- (constant CO2) had little effect on beta-IC Vbl, whereas alpha-IC Vbl depolarized by 5.2 +/- 0.7 mV. Reducing luminal HCO3- in the absence of luminal Cl- produced a 17.6 +/- 1.8 mV depolarization in beta-IC. This change was independent of luminal Na+ and was not blocked by luminal 10(-4) M 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). In beta-IC, Vbl was not altered by either bath or lumen DIDS in the presence of luminal Cl-. However, when luminal Cl- was removed, luminal DIDS reversibly depolarized Vbl by 9.6 +/- 2.9 mV.(ABSTRACT TRUNCATED AT 250 WORDS)
To examine the exact target cell and mechanism of action of epidermal growth factor (EGF) in the isolated cortical collecting duct from rabbit kidney, we compared electrical properties of collecting duct (CD) cells (principal cells) and intercalated (IC) cells in absence and presence of EGF at 10(-8) M. Differentiation of CD and IC cells was based on values of basolateral membrane voltage (Vb) and fractional apical membrane resistance (fRa). In CD cells, upon addition of EGF to bath, lumen-negative transepithelial voltage (VT) was decreased from -8.0 +/- 1.9 to -2.4 +/- 1.3 mV (n = 22, P less than 0.001), but Vb was little changed (from -85.1 +/- 2.8 to -83.1 +/- 2.7 mV, n = 19), indicating that EGF in bath mainly caused changes in apical membrane voltage. In addition, peritubular EGF increased transepithelial resistance (RT) from 132.9 +/- 15.8 to 153.8 +/- 18.4 omega.cm2 (n = 16, P less than 0.001) as well as fRa from 0.31 +/- 0.06 to 0.39 +/- 0.07 (n = 12, P less than 0.01). These actions of EGF were prevented by pretreatment with 50 microM luminal amiloride. Luminal EGF had no effects on VT, Vb, RT, or fRa of CD cells. In IC cells, upon addition of EGF to bath, neither Vb nor fRa was affected. From these results, we conclude that EGF acts on the CD cell at the basolateral border and inhibits mainly the amiloride-sensitive Na+ conductance in the apical membrane.
We developed a new optical device (Nikkiso) to assess changes through blood volume monitoring (BVM) during hemodialysis and were able to determine the ideal levels in which changes in blood volume percentage (BV%) occur among hemodialysis patients in one hemodialysis center. We evaluated both the reliability of BVM and these ideal levels in a multicenter group. The purpose of this manuscript is to develop a navigating system to set dry weight in a variety of situations as the final goal. First, based on the obtained BVM (BV%(BVM) ) measurements, the relationships between BV% and hematocrit (BV%(HT) ) and between BV% and CRIT-LINE (BV%(CLM) ; Hema Metrics, Kaysville, UT, USA) were then evaluated. In 30 hemodialysis patients, there was a close correlation between both BV%(BVM) vs. BV%(HT) and BV%(BVM) vs. BV%(CLM) (n=30, r=0.967, P<0.001, and n=36, r=0.7867, P<0.001, respectively). Second, BV% data were obtained from 464 treatment cases performed on 26 subjects in one satellite hemodialysis center on patients whose body weight was deemed clinically suitable. The formulas for the levels of BV% (standardized by the percent change in body weight at the end of hemodialysis treatment: BW%end) were determined. Finally, we revalidated the reliability of the above levels. A total of 1126 measurements were performed on 201 patients whose body weights were deemed suitable in seven hemodialysis centers. New ideal levels were then recalculated. We therefore conclude that BVM is a sufficiently accurate method of monitoring BV% in hemodialysis treatment. Most well-controlled hemodialysis patients display the same pattern of BV%/BW%end. Monitoring BV% during hemodialysis is beneficial for determining dry weight (DW).
Epidermal growth factor (EGF) inhibits amiloride-sensitive Na+ conductance in the apical membrane of the isolated rabbit cortical collecting duct. However, there is no information on the relationship between electrolyte transport and tyrosine kinase. We examined the effect of EGF on transport of potassium and chloride as well as sodium and the roles of tyrosine kinases in the rabbit cortical collecting duct using in vitro isolated tubular microperfusion. Basolateral EGF depolarized the transepithelial voltage in a dose-dependent manner within a concentration range of 10−10 in 10−8 M. Basolateral ouabain and luminal amiloride completely abolished EGF-induced depolarization. However, luminal BaCl2 did not abolish its depolarization. To confirm the mechanism, sodium, potassium, and chloride fluxes were measured in the presence of 10−10M EGF. EGF significantly decreased the lumen-to-bath isotope flux of sodium and chloride from 93.6±12.5 to 61.1±9.6 pmol/mm/min (n = 5, p<0.05) and from 86.6±10.0 to 54.8±9.7 pmol/mm/min (n = 10, p<0.01), respectively. EGF also decreased net potassium secretion from −27.7±5.9 to –7.8±1.5 pmol/mm/min (n = 6, p<0.01). To examine whether EGF-induced depolarization is mediated by tyrosine kinase, tyrosine kinase inhibitors were applied from the basolateral side. Pretreatment with 1 µg/ml herbimycin A for 120 min completely abolished EGF-induced depolarization (90.9±5.4%, n = 4; NS). Herbimycin A itself also did not change the lumen-to-bath isotope flux of sodium and completely abolished the inhibition of Na+ absorption on EGF action (control 65.4±6.8, herbimycin A 61.8±6.3, EGF with herbimycin A 60.0±4.4 pmol/min/mm, n = 5; NS). In conclusion, EGF depolarizes transepithelial voltage by inhibiting sodium transport primarily and potassium and chloride transport secondarily. These effects were blocked by nonspecific tyrosine kinase inhibitors.
The role of metabolic acidosis in the regulation of transepithelial potassium transport was examined in rabbit cortical collecting ducts (CCD) using in vitro isolated tubular microperfusion and conventional microelectrode techniques. Basolateral metabolic acidosis, created by reduction of bicarbonate concentration from 25 to 5 meq/l, pH 7.40 to 6.80, depolarized the transepithelial voltage significantly (-6.5 +/- 1.0 to -2.7 +/- 1.3 mV). Basolateral acidosis also suppressed net potassium secretion (-14.3 +/- 2.1 to -9.0 +/- 1.7 pmol.min-1.mm-1). Electrophysiological study in CCD cells demonstrated that basolateral metabolic acidosis depolarized transepithelial voltage and apical and basolateral membrane voltage with an increase of transepithelial and fractional apical resistance. Basolateral acidosis did not affect the 22Na efflux nor 86Rb efflux. The inhibitory action of basolateral acidosis on net potassium secretion remained in the presence of luminal barium and in the absence of bicarbonate. Ouabain could not abolish the effect of basolateral acidosis on transepithelial voltage completely. These data lead us to conclude that basolateral acidosis affects multiple transport pathways, and it inhibits mainly apical barium-sensitive potassium transport. Additionally, it inhibits apical sodium conductance, barium-insensitive potassium transport, and stimulates a ouabain-insensitive electrogenic transport pathway to some degree.
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