Whole cell recording of sugar-induced currents in LLC-PK1 cells.
Gigaohm-seal whole cell recording techniques were used to monitor function of the Na(+)-coupled sugar transport system in LLC-PK1 cells. The currents coupled to sugar transport were identified as those that are induced by the presence of 10 mM alpha-methylglucoside (AMG) in either the extracellular or intracellular compartment and were inhibited by addition of 320-800 microM phlorizin to the extracellular bathing medium. The sugar-induced currents are small, 15-20 pA, but of the expected magnitude as determined from the known kinetic parameters for Na(+)-coupled sugar transport in LLC-PK1 cells. The phlorizin-sensitive currents are Na+ dependent and can be studied under conditions in which the net Na+ and sugar flux (and consequently the Na+ electrical current) is in either the inward or outward direction. The reversal potential of the sugar-induced currents measured under conditions with high Na+ and AMG concentrations inside the cell is close to values predicted from thermodynamic principles, assuming a coupling stoichiometry of 2 Na+: 1 sugar for the transport system. The reversal potential of the sugar-induced currents with high extracellular Na+ and AMG is not equal to the predicted value, but it is of the polarity expected for inward-imposed solute gradients. Reasons for the observed discrepancy between observed and calculated values are discussed.
Smith-Maxwell
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Department of Biophysics, School of Medicine and Dentistry, University of Rochester, New York 14642.
Bennett
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E
Randles
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Kimmich
G A
GA
D000818:Animals; D002460:Cell Line; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008757:Methylglucosides / Q000378:metabolism / Q000494:pharmacology*; D008759:Methylglycosides / Q000494:pharmacology*; D010695:Phlorhizin / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology
D008757:Methylglucosides; D008759:Methylglycosides; C027020:methylglucoside; D012964:Sodium; D010695:Phlorhizin