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Calcium influx in internally dialyzed squid giant axons.

Calcium influx in internally dialyzed squid giant axons. A method has been developed to measure Ca influx in internally dialyzed squid axons. This was achieved by controlling the dialyzed segment of the axon exposed to the external radioactive medium. The capacity of EGTA to buffer all the Ca entering the fiber was explored by changing the free EGTA at constant Ca++i. At a free EGTAi greater than 200 microM, the measured resting Ca influx and the expected increment in Ca entry during electrical stimulation were independent of the axoplasmic free EGTA. To avoid Ca uptake by the mitochondrial system, cyanide, oligomycin, and FCCP were included in the perfusate. Axons dialyzed with a standard medium containing: ATP = 2 mM, Ca++i = 0.06 microM, Ca++o = 10 mM, Na+i = 70 mM, and Na+o = 465 mM, gave a mean Ca influx of 0.14 +/- 0.012 pmol.cm-2.s-1 (n = 12. Removal of ATP drops the Ca influx to 0.085 +/- 0.007 pmol.cm-2.s-1 (n = 12). Ca influx increased to 0.35 pmol.cm-2,s-1 when Nao was removed. The increment was completely abolished by removing Nai+ and (or) ATP from the dialysis medium. At nominal zero Ca++i, no Nai-dependent Ca influx was observed. In the presence of ATP and Nai Ca++i activates the Ca influx along a sigmoid curve without saturation up to 1 microM Ca++i. Removal of Nai+ always reduced the Ca influx to a value similar to that observed in the absence of Ca++i (0.087 +/- 0.008 pmol.cm-2.s-1; n = 11). Under the above standard conditions, 50-60% of the total Ca influx was found to be insensitive to Nai+, Cai++, and ATP, sensitive to membrane potential, and partially inhibited by external Co++. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of General Physiology Rockefeller University Press

Calcium influx in internally dialyzed squid giant axons.

DiPolo, R
The Journal of General Physiology , Volume 73 (1): 91 – Jan 1, 1979
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Publisher
Rockefeller University Press
Copyright
© 1979 Rockefeller University Press
ISSN
0022-1295
eISSN
1540-7748
DOI
10.1085/jgp.73.1.91
Publisher site
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Abstract

A method has been developed to measure Ca influx in internally dialyzed squid axons. This was achieved by controlling the dialyzed segment of the axon exposed to the external radioactive medium. The capacity of EGTA to buffer all the Ca entering the fiber was explored by changing the free EGTA at constant Ca++i. At a free EGTAi greater than 200 microM, the measured resting Ca influx and the expected increment in Ca entry during electrical stimulation were independent of the axoplasmic free EGTA. To avoid Ca uptake by the mitochondrial system, cyanide, oligomycin, and FCCP were included in the perfusate. Axons dialyzed with a standard medium containing: ATP = 2 mM, Ca++i = 0.06 microM, Ca++o = 10 mM, Na+i = 70 mM, and Na+o = 465 mM, gave a mean Ca influx of 0.14 +/- 0.012 pmol.cm-2.s-1 (n = 12. Removal of ATP drops the Ca influx to 0.085 +/- 0.007 pmol.cm-2.s-1 (n = 12). Ca influx increased to 0.35 pmol.cm-2,s-1 when Nao was removed. The increment was completely abolished by removing Nai+ and (or) ATP from the dialysis medium. At nominal zero Ca++i, no Nai-dependent Ca influx was observed. In the presence of ATP and Nai Ca++i activates the Ca influx along a sigmoid curve without saturation up to 1 microM Ca++i. Removal of Nai+ always reduced the Ca influx to a value similar to that observed in the absence of Ca++i (0.087 +/- 0.008 pmol.cm-2.s-1; n = 11). Under the above standard conditions, 50-60% of the total Ca influx was found to be insensitive to Nai+, Cai++, and ATP, sensitive to membrane potential, and partially inhibited by external Co++.

Journal

The Journal of General Physiology – Rockefeller University Press

Published: Jan 1, 1979

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