Effect of Quin-2 on 45Ca2+ uptake mediated by Na+i/Ca2+o exchange and 45Ca2+ efflux in rat brain synaptosomes: a requirement for [Ca2+]i.
The Na+/Ca2+ exchanger of squid axons, barnacle muscle and sarcolemma requires micromolar intracellular calcium for activation in the Na+i/Ca2+o exchange mode ('reverse' Na+/Ca2+ exchange). The requirement for [Ca2+]i has been demonstrated with the use of intracellular calcium buffers, such as Quin-2, to inhibit Na+i/Ca2+o exchange. However, the inhibition of Na+i/Ca2+o exchange in mammalian nerve terminals loaded with Quin-2 has not been observed [7], suggesting a lower sensitivity to low [Ca2+]i for this system. In contrast, the results reported herein indicate that 45Ca2+ uptake in synaptosomes through Na+i/Ca2+o exchange is inhibited by Quin-2 much in the same way as it is in the squid, provided that synaptosomes are preincubated in low Ca2+ medium to avoid saturation of Quin-2. Under these conditions, 45Ca2+ efflux via Ca2+i/Ca2+o exchange is also inhibited. Our results indicate that the Na+i/Ca2+o and Ca2+i/Ca2+o modes of the Na+/Ca2+ exchanger from rat brain synaptosomes require intracellular calcium for activation. However, because no clear relationship between the observed [Ca2+]i values and the inhibition of Na+i/Ca2+o exchange has been found, it is suggested that localised submembrane calcium concentrations not detected by the [Ca2+]i probe might regulate the exchanger.
Blanco
P
P
Departamento de Biología Molecular, Universidad Autónoma de Madrid, Spain.
Martínez-Serrano
A
A
Bogónez
E
E
Satrústegui
J
J
D000634:Aminoquinolines / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D000634:Aminoquinolines; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D012964:Sodium; C035739:Quin2; D011188:Potassium; D002118:Calcium