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  • 1
    Electronic Resource
    Electronic Resource
    The pH-sensitivity of transepithelial K+ transport in vestibular dark cells (1995)
    Springer
    The journal of membrane biology 147 (1995), S. 255-262 
    Details
    ISSN: 1432-1424
    Keywords: Labyrinth ; Slowly activating K+ channel ; IsK channel ; MinK channel ; pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The pH-sensitivity of transepithelial K+ transport was studied in vitro in isolated vestibular dark cell epithelium from the gerbil ampulla. The cytosolic pH (pH iwas measured microfluorometrically with the pH-sensitive dye 2′,7′-bicarboxyethyl-5(6)-carboxyfluorescein (BCECF) and the equivalent short-circuit current (I sc), which is a measure for transepithelial K+ secretion, was calculated from measurements of the transepithelial voltage (V t)and the transepithelial resistance (R t) in a micro-Ussing chamber. All experiments were conducted in virtually HCO 3 − -free solutions. Under control conditions, pH iwas 7.01±0.04 (n=18), V twas 9.1±0.5 mV, R t16.7±0.09 Ωcm2, and I sc was 587±30 μA/cm2 (n=49). Addition of 20 mm propionate− caused a biphasic effect involving an initial acidification of pH i, increase in V tand I sc and decrease in R tand a subsequent alkalinization of pH i, decrease of V tand increase of R t. Removal of propionate− caused a transient effect involving an alkalinization of pH i, a decrease of V tand I sc and an increase in R t. pH iin the presence of propionate− exceeded pH iunder control conditions. Effects of propionate − on V t, R tand I sc were significantly larger when propionate− was applied to the basolateral side rather than to the apical side of the epithelium. The pH i-sensitivityof I sc between pH 6.8 and 7.5 was −1089 μA/(cm2 · pH-unit) suggesting that K+ secretion ceases at about pH i7.6. Acidification of the extracellular pH (pH o)caused an increase of V tand I sc and a decrease of R tmost likely due to acidification of pH i. Effects were significantly larger when the extracellular acidification was applied to the basolateral side rather than to the apical side of the epithelium. The pH osensitivity of I sc between pH 7.4 and 6.4 was −155 μA/(cm2 · pH unit). These results demonstrate that transepithelial K+ transport is sensitive to pH iand pH oand that vestibular dark cells contain propionate− uptake mechanism. Further, the data suggest that cytosolic acidification activates and that cytosolic alkalinization inactivates the slowly activating K+ channel (I sK)in the apical membrane. Whether the effect of pH ion the I sK channel is a direct or indirect effect remains to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234523
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  • 2
    Electronic Resource
    Electronic Resource
    K+ Secretion in Strial Marginal Cells is Stimulated via β1-Adrenergic Receptors but not via β2-Adrenergic or Vasopressin Receptors (2000)
    Springer
    The journal of membrane biology 175 (2000), S. 191-202 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Stria vascularis — Receptor — Adrenergic — Beta — Beta-antagonists — Adrenergic — Atenolol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Pharmacologic tools were used to identify receptors in functional studies by measuring either transepithelial current (I sc ) in strial marginal cells (SMC) or cAMP production in stria vascularis (SV). Further, receptors were identified in SV as transcripts by cloning and sequencing of reverse-transcriptase polymerase chain reaction (RT-PCR) products. Experiments were performed using tissues isolated from gerbils unless specified otherwise. I sc under control conditions was 1090 ± 21 μA/cm2 (n= 213) in gerbil SMC and 2001 ± 95 μA/cm2 (n= 6) in murine SMC. Direct stimulation of adenylate cyclase with 10-5 m forskolin but not with 10−5 m 1,9-dideoxy-forskolin resulted in an increase in the I sc by a factor of 1.14 ± 0.01 (n= 6). The vasopressin-receptor agonist 10−8 m Arg8-vasopressin had no significant effect on I sc in gerbil and murine SMC. The β-adrenergic agonists isoproterenol, norepinephrine and epinephrine stimulated I sc with an EC 50 of (6 ± 2) × 10−7 m (n= 28), (3 ± 1) × 10−6 m (n= 40) and (7 ± 2) × 10−6 m (n= 38), respectively. Isoproterenol stimulated cAMP production in SV with an EC 50 of (5 ± 2) × 10−7 m (n= 8). The β-antagonist 10−4 m propanolol completely inhibited 2 × 10−5 m isoproterenol-induced stimulation of I sc . The β-antagonists atenolol, ICI118551 and CGP20712A inhibited isoproterenol-induced stimulation of I sc with a K DB of 1 × 10−7 m (pK DB = 6.96 ± 0.15, n= 14), 1 × 10−7 m (pK DB = 7.01 ± 0.14, n= 15), 2 × 10−9 m (pK DB = 8.73 ± 0.13, n = 19), respectively. CGP20712A inhibited isoproterenol-induced cAMP production with a K DB of 1 × 10−10 m (pK DB = 9.94 ± 0.55, n= 9). RT-PCR of total RNA isolated from SV using primers specific for the β1-, β2- and β3-adrenergic receptors revealed products of the predicted sizes for the β1- and β2- but not the β3-adrenergic receptor. Sequence analysis confirmed that amplified cDNA fragments encoded gene-specific nucleotide sequences. These results demonstrate that K+ secretion in SMC is under the control of β1-adrenergic receptors but not β2-adrenergic or vasopressin-receptors and that the β1-subtype is the primary β-adrenergic receptor in SV although SV contains transcripts for both β1- and β2-adrenergic receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00232001067
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  • 3
    Electronic Resource
    Electronic Resource
    Differential effects of ADH on sodium, chloride, potassium, calcium and magnesium transport in cortical and medullary thick ascending limbs of mouse nephron (1988)
    Springer
    Pflügers Archiv 412 (1988), S. 516-523 
    Details
    ISSN: 1432-2013
    Keywords: ADH ; Transepithelial ion net fluxes ; Na+, Cl−, K+, Ca2+ and Mg2+ transport ; Electron microprobe ; Mouse kidney ; Cortical and medullary thick ascending limb of Henle's loop ; In vitro microperfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of antidiuretic hormone (arginine vasopressin, AVP) on transepithelial Na+, Cl−, K+, Ca2+ and Mg2+ net transports was investigated in medullary (mTAL) and cortical (cTAL) segments of the thick ascending limb (TAL) of mouse nephron, perfused in vitro. Transepithelial net fluxes (J Na +,J Cl −,J K +,J Ca 2+,J Mg 2+) were determined by electron probe analysis of the collected tubular fluid. Transepithelial potential difference (PDte) and transepithelial resistance (Rte) were measured simultaneously. cTAL segments were bathed and perfused with isoosmolal, HCO 3 − containing Ringer solutions, mTAL segments were bathed and perfused with isoosmolal HCO 3 − free Ringer solutions. In cTAL segments, AVP (10−10 mol·l−1) significantly increasedJ Mg 2+ andJ Ca 2+ from 0.39±0.08 to 0.58±0.10 and from 0.86±0.13 to 1.19±0.15 pmol·min−1 mm−1 respectively. NeitherJ Na + norJ Cl −, (J Na +: 213±30 versus 221±28 pmol·min−1 mm−1,J Cl −: 206±30 versus 220±23 pmol·min−1 mm−1) nor PDte (13.4±1.3 mV versus 14.1±1.9 mV) or Rte (24.6±6.5Ω cm2 versus 22.6±6.4Ω cm2) were significantly changed by AVP. No significant effect of AVP on net K+ transport was observed. In mTAL segments, Mg2+ and Ca2+ net transports were close to zero and AVP (10−10 mol·l−1) elicited no effect. However NaCl net reabsorption was significantly stimulated by the hormone,J Na + increased from 107±33 to 148±30 andJ Cl − from 121±33 to 165±32 pmol·min−1 mm−1. The rise inJ NaCl was accompanied by an increase in PDte from 9.0±0.7 to 13.5±0.9 mV and a decrease in Rte from 14.4±2.0 to 11.2±1.7 Ω cm2. No K+ net transport was detected, either under control conditions or in the presence of AVP. To test for a possible effect of HCO 3 − on transepithelial ion fluxes, mTAL segments were bathed and perfused with HCO 3 − containing Ringer solutions. With the exception ofJ Ca 2+ which was significantly different from zero (J Ca 2+: 0.26±0.06 pmol·min−1 mm−1), net transepithelial fluxes of Na+, Cl−, K+ and Mg2+ were unaffected by HCO 3 − . In the presence of AVP,J Mg 2+ andJ Ca 2+ were unaltered whereasJ NaCl was stimulated to the same extent as observed in the absence of HCO 3 − . In conclusion our results indicate heterogeneity of response to AVP in cortical and medullary segments of the TAL segment, since AVP stimulates Ca2+ and Mg2+ reabsorption in the cortical part and Na+ and Cl− reabsorption in the medullary part of this nephron segment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582541
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