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.