Calcium influx in internally dialyzed squid giant axons
نویسنده
چکیده
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 [EGTA]i 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++.
منابع مشابه
Calcium Influx in Internally Dialyzed Squid Giant Axons
I N T R O D U C T I O N Since the f inding that a fraction o f the Ca efflux in squid axons might be involved in a N a < o u p l e d exchange mechanism (Blaustein and Hodgkin , 1969) a great deal o f work has been devoted to analyze this particular unidirectional Ca f u x . Al though not all the features o f the Ca efflux have been firmly established, most o f the quantitative dependencies on N...
متن کاملCalcium Efflux from Internally Dialyzed Squid Giant Axons
Calcium efflux has been studied in squid giant axons under conditions in which the internal composition was controlled by means of a dialysis perfusion technique. The mean calcium efflux from axons dialyzed with 0.3 microM calcium and 5 mM ATP was 0.26 pmol/cm(2).s at 22 degrees C. The curve relating the Ca efflux with the internal Ca concentration had a slope of about one for [Ca](i) lower tha...
متن کاملCalcium Influx in Internally Dialyzed Squid Giant Axons
I N T R O D U C T I O N Since the f inding that a fraction o f the Ca efflux in squid axons might be involved in a N a < o u p l e d exchange mechanism (Blaustein and Hodgkin , 1969) a great deal o f work has been devoted to analyze this particular unidirectional Ca f u x . Al though not all the features o f the Ca efflux have been firmly established, most o f the quantitative dependencies on N...
متن کاملEffect of ATP on the Calcium Efflux in Dialyzed Squid Giant Axons
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 2...
متن کاملCharacterization of the ATP-dependent calcium efflux in dialyzed squid giant axons
The magnitude of the activating effect of ATP on the Ca efflux was explored at different [Ca++]i in squid axons previously exposed to cyanide seawater and internally dialyzed with a medium free of ATP and containing p-trifluoro methoxy carbonyl cyanide phenyl hydrazine. At the lowest [Ca++]i used (0.06 micron more than 95% of the Ca efflux depends on ATP. At high [Ca++]i (100 micron), 50-60% of...
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عنوان ژورنال:
- The Journal of General Physiology
دوره 73 شماره
صفحات -
تاریخ انتشار 1979