Potassium conductances in cultured bovine and human retinal pigment epithelium.
OBJECTIVE
To identify K+ conductances on the apical and basolateral membranes in cultured monolayers of fetal bovine and human retinal pigment epithelium (RPE).


METHODS
Bovine and human RPE cells were grown on a permeable substrate for an average of 4 and 25 months, respectively, mounted in a modified Ussing chamber that allowed rapid solution changes at both membranes, and perfused with modified Ringer's solutions. Conventional microelectrode recording techniques were used to record intracellularly from RPE cells.


RESULTS
Electrical parameters under control conditions for bovine (n = 11) and human (n = 7) cultures respectively, were: transepithelial potential, 0.6 +/- 0.2 and 3.2 +/- 0.5 mV; Rt, 70 +/- 12 and 227 +/- 30 ohm.cm2; and Vap, -61 +/- 3 and -51 +/- 2 mV (mean +/- SEM). The relative K+ conductance (TK) was estimated from responses to 10-fold increases in [K+]o. For the apical and basal membranes, the values for TK were 0.65 and 0.37, respectively, in bovine and 0.33 and 0.45, respectively, in human RPE. Barium applied to either surface of the cultures produced membrane depolarizations and suppressed the responses significantly to K+. In bovine, a 10-fold decrease in basal [K+]o hyperpolarized Vba by 2 +/- 1 mV; a similar decrease in apical [K+]o hyperpolarized Vap by 14 +/- 1 mV. At both membranes, perfusion with Ba2+ unmasked a significant membrane depolarization induced by lowering [K+]o; this phenomenon, observed previously at the apical membrane in fresh explant bovine, frog, and toad RPE, appears to be an unmasking of Na+/K+ pump modulation by K+.


CONCLUSIONS
These results indicate the presence of Ba2+ sensitive K+ conductances at the apical and basal membranes of confluent monolayers of cultured fetal human and bovine RPE and the presence of Na+/K+ pump sites at both membranes of cultured bovine cells.
Hernandez
E V
EV
Jules Stein Eye Institute, University of California, Los Angeles School of Medicine.
Hu
J G
JG
Frambach
D A
DA
Gallemore
R P
RP
D000818:Animals; D001693:Biological Transport, Active; D002417:Cattle; D002478:Cells, Cultured; D005333:Fetus; D006801:Humans; D017136:Ion Transport; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D015221:Potassium Channels; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium