Channel-mediated and carrier-mediated uptake of K+ into cultured ovine oligodendrocytes.
Uptake of radioactive K+ by mature ovine oligodendrocytes (OLGs) maintained in primary culture was measured under steady-state conditions, i.e., in cells maintained in a normal tissue culture medium (5.4 mM K+), and in cells after depletion of intracellular K+ to less than 15% of its normal value by pre-incubation in K(+)-free medium. The latter value is dominated by an active, carrier-mediated uptake (although it may include some diffusional uptake), whereas the former, in addition to active uptake, also reflects passive K+ diffusion through ion selective channels and possible self-exchange between extracellular and intracellular K+, which may be carrier-mediated. The total uptake rate was 144 +/- 10 nmol/min/mg protein, and the uptake after K+ depletion was 60 +/- 2 nmol/min/mg protein, much lower rates than previously observed in astrocytes. The uptake into K(+)-depleted cells was inhibited by about 80% in the presence of ouabain (1 mM) and about 30% in the presence of furosemide (2 mM). Activators of protein kinase C (phorbol esters) and cAMP-dependent protein kinase (forskolin) have been shown to alter the myelinogenic metabolism as well as outward K+ current in cultured OLGs. The present study demonstrates that K+ homeostasis in OLGs is modulated through similar second messenger pathways. Active uptake was inhibited by about 60% in the presence of active phorbol esters (100 nM) but was not affected by forskolin (100 nM). Forskolin likewise had no effect on total uptake, whereas phorbol esters caused a much larger inhibition than expected from their effect on carrier-mediated uptake alone, suggesting that channel-mediated uptake was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)
Hertz
L
L
Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada.
Soliven
B
B
Hertz
E
E
Szuchet
S
S
Nelson
D J
DJ
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009836:Oligodendroglia / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D011197:Potassium Radioisotopes; D011493:Protein Kinase C / Q000502:physiology; D012756:Sheep; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D015221:Potassium Channels; D011197:Potassium Radioisotopes; D005576:Colforsin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium