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  • Title: The effect of EGF on electrolyte transport is mediated by tyrosine kinases in the rabbit cortical collecting duct.
    Author: Ookawara S, Tabei K, Furuya H, Asano Y.
    Journal: Miner Electrolyte Metab; 1999; 25(3):191-8. PubMed ID: 10436405.
    Abstract:
    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 BaCl(2) did not abolish its depolarization. To confirm the mechanism, sodium, potassium, and chloride fluxes were measured in the presence of 10(-10) M 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 microg/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.
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