Electrogenic transport of neutral and dibasic amino acids in a cultured opossum kidney cell line (OK)

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Abstract
A study has been made of electrogenic cellular uptake of amino acids resulting in the depolarization of cell membrane potential (PDm) in confluent monolayers of an established opossum kidney (OK) cell line using conventional and pH-selective microelectrodes. Apical superfusion of neutral and dibasic amino acids rapidly depolarized the cell membrane, while application of acidic amino acids had no effect on PDm. The depolarization in response toL-phenylalanine andL-arginine was stereoselective, dose-dependent and saturable. 10 mmol/l ofL-phenylalanine reduced PDm by 4.8±0.4 mV (n=51) in a completely sodium-dependent way and the concentration necessary for halfmaximal depolarization (C1/2) was about 1.5 mmol/l. On the other hand, the C1/2 forL-arginine was about 0.02 mmol/l. The maximal depolarization produced byL-arginine (measured at 10 mmol/l) amounted to 6.8±1.2 mV (n=10) and this was not affected when extracellular sodium was replaced by choline (6.3±1.2 mV;n=10). The depolarizations induced byL-phenylalanine andL-arginine were significantly additive (pn=11) and did not change duringL-arginine application. We conclude that (1) carrier-mediated uptake of neutral and dibasic amino acids into OK cells is at least partially electrogenic. (2)L-Phenylalanine is transported by a Na+-symport. (3) In contrast,L-arginine depolarizes PDm independently of extracellular sodium. (4) Electrogenic uptake of acidic amino acids is not detectable in OK cells.