Calcium and EDTA fluxes in dialyzed squid axons.
Ca efflux in dialyzed squid axons was measured with 45Ca as a function of internal ionized Ca in the range 0.005-10 muM. Internal Ca stores were depleted by treatment with CN and dialysis with media free of high energy compounds. The [Ca]iota was stabilized with millimolar concentrations of EDTA, EGTA, or DTPA. Nonspecific leak of chelated Ca was measured with [14C]-EDTA and found to be 0.02 pmol/cm2s/mM EDTA. Correction of the measured Ca efflux for this leak of chelated calcium was made when appropriate. Ca efflux was roughly linear with internal free Ca in the range 0.005-0.1 muM. Above 0.1 muM, efflux was less than proportional to concentration but did not saturate at the highest concentration studied. Ca efflux was reduced about 50% by replacement of external Na with Li at Caiota approximately 1 muM, but was insensitive to such replacement for Ca less than 0.1 muM. Ca efflux was insensitive to internal Mg in the range 0-4 mM, indicating that the Ca pump favors Ca over Mg by a factor of about 10(6). Ca efflux was reduced about 60% by increasing internal Na from 1 to 80 mM. This effect could represent weak interference of a Ca carrier by Na or a loss of driving force because of a reduction in ENa - Em occasioned by an increase in Naiota. A few measurements were made of Ca influx in intact and in dialyzed fibers. In both cases, Ca influx increased when external Na was replaced by Li.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D049832:Decapodiformes; D003956:Dialysis; D004492:Edetic Acid / Q000378:metabolism*; D004533:Egtazic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism; D012623:Seawater; D012964:Sodium / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
D004533:Egtazic Acid; D013395:Sucrose; D007811:Lanthanum; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D012964:Sodium; D008274:Magnesium; D002118:Calcium