The Na+-Ca2+ exchange system in rat glial cells in culture: Activation by external monovalent cations
✍ Scribed by Andrea Holgado; Luis Beaugé
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 1016 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
Cultured rat glial cells display a Na+-Ca2+ exchange system located at the plasma membrane levels. This was evidenced by the Na+ (+dependency of a Na+ (0)-inhibitable influx of Ca2+, or reversal exchange mode. This antiporter has an external site where monovalent cations (K+, Li+, and Na+ were investigated) stimulate the exchange by a chemical action. The monovalent cation is not transported during the exchange cycle. The mechanism of that stimulation agrees with an increase in the apparent affinity of the carrier for Ca2+(o) without effect on the maximal translocation rate. Two models can equally well account for the data: i) the formation of ECa(o) is essential for the binding of the monovalent cation, or ii) the activating cation can bind even when the carrier is free of Ca2+(o). The cations K+ and Li+ produced only stimulation, although that of K+ seem to require actions other than the chemical effect. The response to Na+ was biphasic; this can be fully explained considering that at low concentrations, Na+(o) binds preferentially to the activating monovalent site while at high concentrations it displaces Ca2+ from its external transporting site. Pure type I astrocytes displayed the same Na+-Ca2+ exchange mechanism. o 1995 Wiley-Liss, Inc.