Role of Na+/Ca2+ exchange in [Ca2+]i clearance in rat culture Purkinje neurons requires reevaluation.
Previous studies have shown that in contrast to other neuronal cells, Na(+)/Ca(2+) exchange contributes little to Ca(i)(2+) 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 degrees C. At 20 degrees C, the recovery of the K(+)-induced [Ca(2+)](i) signal was little affected by the presence of external Na(+) (tau(e) = 35.5 +/- 1.2 s [n = 49]), or by its absence (tau(e) = 36.6 +/- 2.2 s [n = 29]), i.e. in a Li(+)-containing medium. In contrast, at 34 degrees C, the recovery of the [Ca(2+)](i) signal was highly dependent on external Na, i.e. tau(e) = 19.9 +/- 1.2 s (n = 119) and tau(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 degrees 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 degrees 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.
Rojas
Héctor
H
Laboratorio de Permeabilidad Ionica, Centro de Biofísica y Bioquímica, IVIC, Apartado 21827, Caracas 1020-A, Venezuela.
Ramos
Magaly
M
Mijares
Alfredo
A
DiPolo
Reinaldo
R
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018929:Cell Culture Techniques; D011689:Purkinje Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D013696:Temperature
D019831:Sodium-Calcium Exchanger; D002118:Calcium