Previous studies have shown that in contrast to other neuronal cells, Na
+/Ca
2+ exchange contributes little to Ca
i2+ homeostasis in rat cerebellar Purkinje neurons under intracellular perfused conditions and at room temperature [Fierro et al.: J Physiol (Lond) 510: 499–512, 1998]. The purpose of this study was to clarify the role of this transporter in cerebellar Purkinje neurons by using intact cells at nearly physiological body temperature. Using Fluo-3 microfluorometry, we have examined the role of the Na
+/Ca
2+ exchange in the buffering of calcium loads in cultured rat Purkinje neurons at two temperatures: 20 and 34°C. At 20°C, the recovery of the K
+-induced [Ca
2+]
i signal was little affected by the presence of external Na
+ (τ
e = 35.5 ± 1.2 s [n = 49]), or by its absence (τ
e = 36.6 ± 2.2 s [n = 29]), i.e. in a Li
+-containing medium. In contrast, at 34°C, the recovery of the [Ca
2+]
i signal was highly dependent on external Na, i.e. τ
e = 19.9 ± 1.2 s (n = 119) and τ
e = 41.7 ± 2.6 s (n = 39), in Li
+-containing media, respectively. A comparison of the rate of clearance of [Ca
2+]
i in Na
+ or Li
+ media, shows that at a room temperature of 20°C, the Na
+/Ca
2+ exchange contributes at most to 15–20% of the total [Ca
2+]
i clearance, compared to 55–65% at 34–36°C. We also demonstrate that under normal physiological conditions forward and reverse Na
+/Ca
2+ exchanges operate in the same neuron. We conclude that the Na
+/Ca
2+ exchange is strongly suppressed at room temperature and therefore its role should be reevaluated among different neuronal preparations.
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