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Effect of ATP on the Calcium Efflux in Dialyzed Squid Giant Axons

Overview
Journal J Gen Physiol
Specialty Physiology
Date 1974 Oct 1
PMID 4418552
Citations 34
Authors
R DiPolo
Affiliations
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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.

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