Channel-mediated and carrier-mediated uptake of K+ into cultured ovine oligodendrocytes
- Univ. of Saskatchewan, Saskatoon (Canada)
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.
- OSTI ID:
- 5982600
- Journal Information:
- Glia (New York); (USA), Vol. 3:6; ISSN 0894-1491
- Country of Publication:
- United States
- Language:
- English
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PHORBOL ESTERS
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POTASSIUM COMPOUNDS
MEMBRANE TRANSPORT
BIOLOGICAL PATHWAYS
HOMEOSTASIS
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PHOSPHOTRANSFERASES
POTASSIUM ISOTOPES
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ENZYMES
ESTERS
ISOTOPE APPLICATIONS
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MAMMALS
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RUMINANTS
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560300* - Chemicals Metabolism & Toxicology
550501 - Metabolism- Tracer Techniques