Characterization of Rb uptake into Sf9 cells using cation chromatography: evidence for a K-Cl cotransporter
2001
Bowles, D.W. | Gillen, C.M.
To assess cation-chloride cotransporter activity in Sf9 cells, cation chromatography was used to measure initial uptake rates of Rb. Rb exchanged with cellular K, with 30% of cellular K replaced after a 40 min exposure to Rb. Rb uptake into Sf9 cells was not inhibited by 50 micromol l-1 ouabain. Rb uptake was approximately 65% inhibited by 250 micromol l-1 bumetanide added to the assay solution, and was more than 95% inhibited when cells were pre-incubated for 20 min with bumetanide (100 and 1000 micromol l-1). Uptake of Rb and Cl followed simple Michaelis-Menten kinetics, with a K(m) for Rb of 17.1+/-2.2 mmol l-1 and a K(m) for Cl of 93.7+/-5.6 mmol l-1. Rb uptake was not dependent upon extracellular Na. Two min exposures to solutions with reduced [Na] or [Cl] produced small but significant changes in cellular Na content. We conclude that the primary Rb uptake pathway in Sf9 cells is a K-Cl cotransporter and that cation chromatography can be used to effectively study kinetic parameters of cotransporter function in tissue culture cells. Characterization of baseline cation-chloride cotransporter activity in Sf9 cells strengthens their utility as a tool for expression and characterization of exogenous proteins.
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