Electrophysiological studies on the evaluation of absorption enhancers in Caco-2 cells using a microelectrode...

We developed a microelectrode technique to characterize the electrophysiological properties in Caco-2 cells, and used it to determine the mechanisms of absorption enhancers. The action of absorption enhancers on the apical membrane of Caco-2 cells was estimated by measuring the apical membrane potential (Vm) with the microelectrode. The Vm value of Caco-2 cells in Hanks' balanced salt solution containing 0.5 mM K+ was 18.9+/-0.8 mV (n=217), and the apical membrane resistance was 49.4+/-1.1 MOhms (n=160). In the electrophysiological study with absorption enhancers, laurylmaltoside (LM) markedly decreased the Vm value, while sodium glycocholate (NaGC) moderately reduced this value, and EDTA did not affect the value. These findings might be associated with their action sites, plasma membrane or tight junction in Caco-2 cell monolayers. In influx and transport studies with these absorption enhancers, LM enhanced the influx of furosemide, which is transported via both the transcellular and paracellular routes into Caco-2 cells, and enhanced its transport to the basolateral side of Caco-2 monolayers more than that of 5(6)-carboxyfluorescein (CF), a paracellular marker. EDTA did not increase the influx of furosemide, and enhanced the transport of furosemide and CF across Caco-2 cell monolayers to the same extent. In contrast, NaGC only slightly increased the influx of furosemide and did not enhance the transport of either furosemide or CF across the Caco-2 monolayers in this study. These findings were well correlated with the effects of these absorption enhancers on the electrophysiological parameters. Therefore, the microelectrode technique might be useful for evaluating the action of absorption enhancers in the plasma membrane at an intact cell level.