Ionic selectivity of the Ca2+/H+ antiport in synaptic vesicles of sheep brain cortex.
As we previously reported, synaptic vesicles isolated from sheep brain cortex contain a Ca2+/H+ antiport that permits Ca2+ accumulation inside the vesicles ( approximately 5 nmol/mg protein) at expenses of the pH gradient generated by the H+-pumping ATPase. We observed that the system associates Ca2+ influx to H+ release and operates with low affinity for Ca2+. In the present work, we found that Ca2+/H+ antiport mediates exchange of protons with other cations such as Zn2+ and Cd2+, suggesting that these cations and Ca2+ share the same transporter molecules to enter the intravesicular space. Zn2+ and Cd2+ induce H+ release in a concentration-dependent manner (fluorimetrically evaluated) and they inhibit the antiport-mediated Ca2+ uptake by the vesicles (isotopically measured). In contrast, large cations such as Ba2+ and Cs+ do not alter Ca2+ influx and they are unable to induce proton release from the vesicles. With respect to Sr2+, which has an intermediary size relatively to the other groups of cations, we found that it does not induce H+ liberation from the vesicles, but it has a concentration-dependent inhibitory effect on the Ca2+-induced H+ release and Ca2+ uptake by the vesicles. These results indicate that the cation selectivity of the synaptic vesicles Ca2+/H+ antiport is essentially determined by the size of the cation transported into the vesicles.
Gonçalves
P P
PP
Centro de Biologia Celular, Departamento de Biologia, Universidade de Aveiro, 3810 Aveiro, Portugal. pgoncalves@bio.ua.pt
Meireles
S M
SM
Neves
P
P
Vale
M G
MG
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000032:analysis* / Q000378:metabolism*; D001464:Barium / Q000493:pharmacokinetics; D001692:Biological Transport / Q000502:physiology; D002104:Cadmium / Q000493:pharmacokinetics; D002118:Calcium / Q000493:pharmacokinetics; D002135:Calcium-Binding Proteins / Q000032:analysis* / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000031:analogs & derivatives / Q000494:pharmacology; D027682:Cation Transport Proteins; D002540:Cerebral Cortex / Q000737:chemistry*; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000502:physiology; D007476:Ionophores / Q000494:pharmacology; D011522:Protons; D012756:Sheep; D013324:Strontium / Q000493:pharmacokinetics; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000737:chemistry* / Q000378:metabolism*; D015032:Zinc / Q000493:pharmacokinetics
D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D007476:Ionophores; D011522:Protons; C027614:calcium-hydrogen antiporters; D002104:Cadmium; D001464:Barium; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D015032:Zinc; D002118:Calcium; D013324:Strontium