Ionized calcium concentrations in squid axons.
Values for ionized [Ca] in squid axons were obtained by measuring the light emission from a 0.1-mul drop of aequorin confined to a plastic dialysis tube of 140-mum diameter located axially. Ionized Ca had a mean value of 20 x 10(-9) M as judged by the subsequent introduction of CaEGTA/EGTA buffer (ratio ca. 0.1) into the axoplasm, and light measurement on a second aequorin drop. Ionized Ca in axoplasma was also measured by introducing arsenazo dye into an axon by injection and measuring the Ca complex of such a dye by multichannel spectrophotometry. Values so obtained were ca. 50 x 10(-9) M as calibrated against CaEGTA/EGTA buffer mixtures. Wth a freshly isolated axon in 10 mM Ca seawater, the aequorin glow invariably increased with time; a seawater [Ca] of 2-3 mM allowed a steady state with respect to [Ca]. Replacement of Na+ in seawater with choline led to a large increase in light emission from aequorin. Li seawater partially reversed this change and the reintroduction of Na+ brought light levels back to their initial value. Stimulation at 60/s for 2-5 min produced an increase in aequorin glow about 0.1% of that represented by the known Ca influx, suggesting operationally the presence of substantial Ca buffering. Treatment of an axon with CN produced a very large increase in aequorin glow and in Ca arsenazo formation only if the external seawater contained Ca.
D000331:Aequorin; D000818:Animals; D001152:Arsenicals; D001369:Axons / Q000378:metabolism*; D001391:Azo Compounds; D002118:Calcium / Q000378:metabolism*; D004396:Coloring Agents; D003486:Cyanides / Q000494:pharmacology; D049832:Decapodiformes; D004533:Egtazic Acid / Q000494:pharmacology; D004558:Electric Stimulation; D008274:Magnesium / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
D001152:Arsenicals; D001391:Azo Compounds; D004396:Coloring Agents; D003486:Cyanides; D000331:Aequorin; D004533:Egtazic Acid; D012964:Sodium; D008274:Magnesium; D002118:Calcium