Novel role of the Ca(2+)-ATPase in NMDA-induced intracellular acidification.

Abstract

The mechanism involved in N-methyl-D-glucamine (NMDA)-induced Ca(2+)-dependent intracellular acidosis is not clear. In this study, we investigated in detail several possible mechanisms using cultured rat cerebellar granule cells and microfluorometry [fura 2-AM or 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-AM]. When 100 microM NMDA or 40 mM KCl was added, a marked increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) and a decrease in the intracellular pH were seen. Acidosis was completely prevented by the use of Ca(2+)-free medium or 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid-AM, suggesting that it resulted from an influx of extracellular Ca(2+). The following four mechanisms that could conceivably have been involved were excluded: 1) Ca(2+) displacement of intracellular H(+) from common binding sites; 2) activation of an acid loader or inhibition of acid extruders; 3) overproduction of CO(2) or lactate; and 4) collapse of the mitochondrial membrane potential due to Ca(2+) uptake, resulting in inhibition of cytosolic H(+) uptake. However, NMDA/KCl-induced acidosis was largely prevented by glycolytic inhibitors (iodoacetate or deoxyglucose in glucose-free medium) or by inhibitors of the Ca(2+)-ATPase (i.e., Ca(2+)/H(+) exchanger), including La(3+), orthovanadate, eosin B, or an extracellular pH of 8.5. Our results therefore suggest that Ca(2+)-ATPase is involved in NMDA-induced intracellular acidosis in granule cells. We also provide new evidence that NMDA-evoked intracellular acidosis probably serves as a negative feedback signal, probably with the acidification itself inhibiting the NMDA-induced [Ca(2+)](i) increase.

• Authors: M L Wu, J H Chen, W H Chen, Y J Chen, K C Chu
• Journal: The American journal of physiology (Am J Physiol) Vol. 277 Issue 4 Pg. C717-27 (10 1999) ISSN: 0002-9513 [Print] United States
• PMID: 10516102 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Acids
• Carbon Dioxide
• N-Methylaspartate
• Potassium Chloride
• Hydrogen
• Calcium-Transporting ATPases
• Calcium

Topics

• Acidosis (chemically induced)
• Acids (metabolism)
• Animals
• Binding Sites
• Calcium (metabolism)
• Calcium-Transporting ATPases (physiology)
• Carbon Dioxide (metabolism)
• Hydrogen (metabolism)
• Hydrogen-Ion Concentration (drug effects)
• Intracellular Membranes (metabolism)
• Mitochondria (metabolism)
• N-Methylaspartate (pharmacology)
• Neurons (metabolism)
• Osmolar Concentration
• Potassium Chloride (pharmacology)
• Rats
• Rats, Wistar