Sodium and potassium uptake in primary cultures of proliferating rat astroglial cells induced by short-term exposure to an astroglial growth factor.
Primary cultures of rat astroglial cells were maintained in a serum-free medium. After 8-10 days of cultivation the cells were exposed to an astroglial growth factor (AGF2) for short periods (1-120 min). Subsequently, uptake of 22Na+ and 42K+ into control and AGF2-pretreated cells was studied. Assay of the Na+ and K+ values in the cells was also performed by atomic absorption spectrometry. Treatment of rat astroglial cells with AGF2 resulted in a significant increase of the uptake of both Na+ and K+ depending on the duration of the exposure period. To reach the maximum increase of cation uptake, 6-10 min and 30 min of AGF2 pretreatment were needed for Na+ and K+, respectively. Amiloride blocked this increase of Na+ and K+ uptake elicited by AGF2 pretreatment, but the control cells were amiloride resistant. Treatment with AGF2 increased the ouabain sensitivity of the K+ uptake as that: 10(-4) M ouabain inhibited K+ uptake of the AGF2-treated cells to the same degree as 5 X 10(-3) M ouabain with the control cells. The Na+ uptake of AGF2-treated cells, however, exhibited no relevant changes in the presence of ouabain. A significant part of the AGF2-induced K+ uptake could be inhibited by both ouabain and amiloride, but a ouabain-resistant and amiloride-sensitive component also was revealed. The furosemide sensitivity of both Na+ and K+ uptake into cultured astroglial cells was also significantly increased by AGF2. Our findings suggest that short-term exposure of cultured glial cells to AGF2 induces these very early ionic events: 1) The appearance of a relevant amiloride-sensitive Na+/H+ exchange, and as a consequence of increased Na+ entry into the cells, secondary activation of the ouabain-sensitive K+ uptake via the Na+,K+-pump. 2) A direct effect of AGF2 on the Na+,K+-pump assembly in the membrane, resulting in increased Na+ sensitivity of the inner pump sites and enhanced ouabain sensitivity of the external K+-binding sites. 3) An increase of ouabain-resistant but amiloride- or furosemide-sensitive Na+ and K+ uptake.
Latzkovits
L
L
Institute of Experimental Surgery, Medical School of Szeged, Hungary.
Torday
C
C
Labourdette
G
G
Pettmann
B
B
Sensenbrenner
M
M
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005665:Furosemide / Q000494:pharmacology; D020904:Glia Maturation Factor; D066298:In Vitro Techniques; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000493:pharmacokinetics*
D020904:Glia Maturation Factor; D009419:Nerve Tissue Proteins; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D011188:Potassium