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 µM) of ATP. The mean calcium efflux from axons dialyzed with 0.3 µM ionized calcium, [ATP]i > 1,000 µM, and bathed in artificial seawater (ASW) was 0.24 ± 0.02 pmol·cm-2·s-1 (P/CS) (n = 8) at 22°C. With [ATP]i < 5 µM 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 µM [ATP]i. An increase of the calcium efflux is observed when [ATP]i is >100 µM and saturates at [ATP]i > 1,000 µM. 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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Selected References
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