Cultured rat astrocytes possess Na+-Ca2+ exchanger

✍ Scribed by Kazuhiro Takuma; Toshio Matsuda; Hitoshi Hashimoto; Shoichi Asano; Professor Akemichi Baba

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 754 KB
• Volume: 12
• Category: Article
• ISSN: 0894-1491
• DOI: 10.1002/glia.440120410

✦ Synopsis

Na+-Ca2+ exchange activity in its reverse mode was demonstrated in cultured rat astrocytes. Combination of ouabain (1 mM) and monensin (20 pM) caused a marked increase in 45Ca2+ uptake in a s t r ~c y t e s . ~~C a ~+ uptake was also stimulated by lowering the external Na+ concentration. Ouabain plus monensin-stimulated 45Ca2+ uptake was blocked by 3,4-dichlorobenzamil (IC50, 16 pM), an inhibitor of Na+-Ca2+ exchanger, but not by nifedipine (0.1 pM). The ~timulated-*~Ca~+ uptake was observed even in K+-free medium, and external K+ at 5-10 mM caused a 2.2-fold increase in the uptake. Microspectrofluorimetry using the Ca2+-sensitive dye fura-2 showed that ouabain plus monensin increased intracellular Ca2+ concentration in single astrocytes. The Ca2+ signal was dependent on external Ca2+ (EC,,, 1.4 mM), and blocked by 20 pM 3,4-dichlorobenzamil, but not by Ca2+ channel blockers (Cd2+, 20 pM; Ni2+, 100 pM). Antiserum of cardiac Na+-Ca2+ exchanger recognized 160 and 120-135 kDa proteins on SDS-polyacrylamide gel electrophoresis of astrocyte homogenate. Northern blot analysis revealed the presence of mRNA for the exchanger protein in astrocytes. These findings indicate that Na+-Ca2+ exchanger which is modulated by K' is present in cultured rat astrocytes.