title: Effect of ATP on the calcium efflux in dialyzed squid giant axons.
abstract: Dialysis perfusion technique makes it possible to control the internal composition of squid giant axons. Calcium efflux has been studied in the presence and in the virtual absence (<5 microM) of ATP. The mean calcium efflux from axons dialyzed with 0.3 microM ionized calcium, [ATP](i) > 1,000 microM, and bathed in artificial seawater (ASW) was 0.24 +/- 0.02 pmol.cm(-2).s(-1) (P/CS) (n = 8) at 22 degrees C. With [ATP](i) < 5 microM the mean efflux was 0.11 +/- 0.01 P/CS (n = 15). The curve relating calcium efflux to [ATP](i) shows a constant residual calcium efflux in the range of 1-100 microM [ATP](i). An increase of the calcium efflux is observed when [ATP](i) is >100 microM and saturates at [ATP](i) > 1,000 microM. The magnitude of the ATP-dependent fraction of the calcium efflux varies with external concentrations of Na(+), Ca(++), and Mg(++). These results suggest that internal ATP changes the affinity of the calcium transport system for external cations.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D049832:Decapodiformes; D066298:In Vitro Techniques; D012964:Sodium / Q000494:pharmacology; D013233:Stellate Ganglion / Q000166:cytology; D013997:Time Factors; D014500:Uracil Nucleotides / Q000494:pharmacology
chemical_list: D014500:Uracil Nucleotides; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium