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

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 to L-phenylalanine and L-arginine was stereoselective, dose-dependent and saturable. 10 mmol/l of L-phenylalanine reduced PDm by 4.8 +/- 0.4 mV (n = 51) in a completely sodium-dependent way and the concentration necessary for half-maximal depolarization (C1/2) was about 1.5 mmol/l. On the other hand, the C1/2 for L-arginine was about 0.02 mmol/l. The maximal depolarization produced by L-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 by L-phenylalanine and L-arginine were significantly additive (p less than 0.001). The intracellular pH of OK cells was 7.09 +/- 0.03 (n = 11) and did not change during L-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.

Properties and Regulation of pH-Dependent Cation Channels in the Apical Membrane of Cultured Proximal Tubule Cells

“…OK cells serve as a model for proximal tubule transport function since they reveal many similarities to proximal tubule cells [4,7,8], OK cells have a pH-dependent Na conduct ance [9], We now show the existence of a nonselective cation channel in the apical membrane of OK cells which is activated by decreased pH,.…”

“…Berlin. Germany) at pH 7.4 as described pre viously in detail [8], For experiments OK cells were seeded in plastic Petri dishes ( 0 3 cm) and used a mini mum o f 3 days after they had reached confluence. Un der these conditions only the apical side o f the cell layer is accessible to the patch pipette.…”

Sodium Conductance in Cultured Proximal Tubule Cells (OK) Is Inhibited by Extracellular Cationic Amino Acids

“…However, the uptake of cationic amino acids into OK cells is neither sodium-depen dent nor electrogenic to a great extent [9]. Our finding that D-isomers are equally effective in reducing the cell membrane conductance in sodium gluconate medium is also not compat ible with the notion of a significant transportinduced charge movement, because the elec trogenic transport of L-amino acids by far exceeds that of the respective D-isomers [8]. Therefore, transport phenomena do not sig nificantly contribute to the overall charge movements under our special experimental conditions.…”

“…Cultured OK cells, a nontransformed renal epithelial cell line derived from the American opossum [5], have been used primarily as a model system to study proximal tubular transport processes for phosphate [6,7] and amino acids [8,9], the regulation of potas sium channels by intracellular calcium [10], stretch [11] and pH [12]. as well as the local ization and activation of the sodium-proton antiporter [13.…”

K⁺-, Cl^–- and Nonselective Channels in Opossum Kidney Cells

“…Over the past years the opossum kidney (OK) cell line [1] has become a widely used model for the investigation of basic proper ties of proximal tubular transport systems such as ion channels [2][3][4], Na+/H+ ex changer [5][6][7][8], Na^-phosphate colransporter [9][10][11] and Na*-coupled amino acid and hexose transporter [12,13].…”