In dialyzed squid axons Ca2+i activates Ca2+o-Na+i and Na+o-Na+i exchanges in the absence of Ca chelating agents.
We used internally dialyzed squid axons to explore whether the reported activatory effect of Ca2+i on the partial reactions of the Na+-Ca2+ exchange (essential activator) is secondary to the presence of Ca2+ chelating agents in the internal medium. The effect of Ca2+i pulses on both the reverse (Ca2+o-dependent Na+ efflux) and Na+-Na+ exchange (Na+o-dependent Na+ efflux) modes of the Na+-Ca2+ exchange was studied in axons dialyzed without EGTA. For these experiments a substantial inhibition of the Ca2+ buffer capacity of the axoplasm was achieved by the use of Ruthenium red (10-20 microM), cyanide (1 mM) and vanadate (1 mM) in the dialysis solution. Our results indicate that the Ca2+i requirement of the reverse and Na+-Na+ exchange can not be explained by a direct inhibition of the Na+-Ca2+ exchanger by EGTA. In fact, both modes of operation of the exchanger can be activated by internal Ca2+ ions in the complete absence of Ca2+ chelating agents thus indicating that the 'catalytic' effect of Ca2+i on the Na+-Ca2+ exchanger is a real phenomenon.
DiPolo
R
R
Centro de Biofisica y Bioquímica, IVIC, Caracas, Venezuela.
Beaugé
L
L
Rojas
H
H
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology*; D049832:Decapodiformes; D004533:Egtazic Acid / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D012964:Sodium / Q000493:pharmacokinetics*; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D002614:Chelating Agents; D008565:Membrane Proteins; D019831:Sodium-Calcium Exchanger; D004533:Egtazic Acid; D012964:Sodium; D002118:Calcium