The effects of manganese and changes in internal calcium on Na-Ca exchange fluxes in the intact squid giant axon.
The effects of manganese chloride were studied on Na-Ca exchange fluxes from intact squid axons. Ca uptakes and Cao-dependent sodium efflux were inhibited half-maximally by 3-7 mM MnCl2. Mn inhibition appears less during Nao-Cai exchange (half-maximal inhibition; 30 mM) than that during Cao-Nai exchange, even when both fluxes were activated with 100 mM Na. The effects of changes in [Ca2+i], effected by Ca-EGTA injection or inhibition of mitochondrial Ca uptake by ruthenium red, were examined on the reverse (Cao-Nai) exchange mode. Ca-EGTA mixtures, designed to raise [Ca2+i] above 2 microM, inhibited Cao-Nai exchange fluxes. Ruthenium red inhibited mitochondrial Ca buffering to effect increases in Cai in the absence of Ca chelators; it activated Nao-Cai exchange fluxes but had little effect on Cao-Nai exchange despite similar reported Km for Cai. The results reflect the difficulty in demonstrating the stimulatory effect of [Ca2+i] on Cao-Nai exchange fluxes in intact axons.
Allen
T J
TJ
Biomedical Sciences Division, King's College London, Strand, U.K.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides; D049832:Decapodiformes; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006706:Homeostasis; D008345:Manganese / Q000494:pharmacology*; D017895:Manganese Compounds; D012430:Ruthenium Red / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger
D002132:Calcium Radioisotopes; D002352:Carrier Proteins; D002712:Chlorides; D017895:Manganese Compounds; D019831:Sodium-Calcium Exchanger; D012430:Ruthenium Red; D008345:Manganese; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D012964:Sodium; C025340:manganese chloride; D002118:Calcium