scholarly journals Calcium efflux from squid axons under constant sodium electrochemical gradient.

1978 ◽  
Vol 72 (4) ◽  
pp. 443-470 ◽  
Author(s):  
J Requena
Keyword(s):  
Appreciable Effect ◽  
Electrochemical Gradient ◽  
Calcium Efflux ◽  
Efflux System ◽  
Giant Axons ◽  
A Value ◽  
Inactivation Constant ◽  
Sigmoid Curve ◽  
Atp Inhibition ◽  
Slight Inhibition

The effect of varying Nao and Nai on Ca efflux while maintaining the ratio Nao/Nai constant was explored in squid giant axons dialyzed with and without ATP. In the absence of ATP, the Ca efflux increased 3.4 +/- 0.2-fold when the Nao/Nai concentrations were reduced from 440/80 to 110/20 mM. In the presence of ATP a similar change did not have an appreciable effect. The inhibition of Ca efflux produced by Nai was studied in the presence and in the absence of ATP. In the absence of ATP, inhibition is very marked and is reminiscent of a unimolecular noncompetitive reaction (inactivation constant [KI] of 34 +/- 5 mM of Nai) whereas in the presence of ATP, the slight inhibition observed indicates that ATP probably increases the KI to 200mM. From the inhibition of the Ca efflux produced by Nai in the presence or absence of ATP a curve describing the dependence of Nai of the ATP-promoted fraction of Ca efflux was constructed. The effect of Nao on the Ca efflux was studied as a function of [Na]i: at low Nai, an activation constant (KA) of 41 mM for Nao was obtained either in the presence of in the absence of ATP. As the intracellular Na is increased in the presence of ATP, Nai seems to have no effect on the apparent half-activation constant. However, in the absence of ATP, the KA for activation increases along a sigmoid curve reaching a value of 112 mM at 100 mM Nai. It is concluded that the Ca efflux system uses the energy of the Na electrochemical gradient. The action of Nai appears to be such that the interaction of a single Na+ is sufficient to block Ca extrusion whereas several Naps externally are necessary to activate Ca extrusion.

scholarly journals Calcium influx in internally dialyzed squid giant axons.

1979 ◽  
Vol 73 (1) ◽  
pp. 91-113 ◽  
Author(s):  
R DiPolo
Keyword(s):  
Electrical Stimulation ◽  
Membrane Potential ◽  
Calcium Influx ◽  
Standard Medium ◽  
Giant Axons ◽  
A Value ◽  
Ca Uptake ◽  
Sigmoid Curve ◽  
O 10

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++.

Preliminary observations on escape swimming and giant neurons in Aglantha digitale (Hydromedusae: Trachylina)

1980 ◽  
Vol 58 (4) ◽  
pp. 549-552 ◽  
Author(s):  
S. Donaldson ◽  
G. O. Mackie ◽  
A. Roberts
Keyword(s):  
Action Potentials ◽  
Giant Axon ◽  
Synaptic Delay ◽  
Giant Axons ◽  
A Value ◽  
Giant Synapses ◽  
Run Up

Aglantha can swim in two ways, one of which, fast swimming, is evoked by contact with predators and serves for escape. The response consists of two or three violent contractions of which the first propels the animal a distance equivalent to five body lengths. Peak velocities in the range 0.3–0.4 m s−1 were measured. Drag is reduced by contraction of the tentacles.Coordination of escape swimming and tentacle contraction is achieved by a system of giant axons. A giant axon runs down each tentacle; action potentials in these elements show a one-for-one correspondence with potentials recorded from a ring-shaped axon lying in the margin near the tentacle bases. The ring giant synapses with eight motor giants which run up the subumbrella innervating the swimming muscles.Conduction velocities in the giant axons may be as high as 4.0 m s−1 in the case of the largest (40 μm diameter) axons. A value of 1.6 ms was obtained for minimum synaptic delay between the ring and motor giant axons.

Calcium efflux in giant axons

1967 ◽  
Vol 135 (2) ◽  
pp. 368-370 ◽  
Author(s):  
M. Luxoro ◽  
S. Rissetti
Keyword(s):  
Calcium Efflux ◽  
Giant Axons

scholarly journals Calcium efflux and cycling across the synaptosomal plasma membrane

1985 ◽  
Vol 226 (1) ◽  
pp. 225-231 ◽  
Author(s):  
R Snelling ◽  
D Nicholls
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
Potential Gradient ◽  
Electrochemical Potential ◽  
Electrochemical Gradient ◽  
Calcium Efflux ◽  
Normal Medium ◽  
Voltage Dependent ◽  
Synaptosomal Plasma Membrane ◽  
Ca2 Channels

Ca2+ efflux from intact synaptosomes is investigated. Net efflux can be induced by returning synaptosomes from media with elevated Ca2+ or high pH to a normal medium. Net Ca2+ efflux is accelerated when the Na+ electrochemical potential gradient is collapsed by veratridine plus ouabain. Under steady-state conditions at 30 degrees C, Ca2+ cycles across the plasma membrane at 0.38 nmol . min-1 . mg-1 of protein. Exchange is increased by 145% by veratridine plus ouabain, both influx and efflux being increased. Increased influx is probably due to activation of voltage-dependent Ca2+ channels, since it is abolished by verapamil. The results indicate that, at least under conditions of low Na+ electrochemical gradient, some pathway other than a Na+/Ca2+ exchange must operate in the plasma membrane to expel Ca2+.

scholarly journals Calcium Efflux from Internally Dialyzed Squid Giant Axons

1973 ◽  
Vol 62 (5) ◽  
pp. 575-589 ◽  
Author(s):  
Reinaldo Dipolo
Keyword(s):  
Calcium Ions ◽  
Initial Rate ◽  
Calcium Efflux ◽  
Perfusion Technique ◽  
Giant Axons ◽  
The Mean ◽  
Per Se ◽  
Internal Sources

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 µM calcium and 5 mM ATP was 0.26 pmol/cm2·s at 22°C. The curve relating the Ca efflux with the internal Ca concentration had a slope of about one for [Ca]i lower than 0.3µM and a slope smaller than one for higher concentrations. Under the above conditions replacement of [Na]o and [Ca]o by Tris and Mg causes an 80% fall in the calcium efflux. When the axons were dialyzed with a medium free of ATP and containing 2 mM cyanide plus 5µg/ml oligomycin, analysis of the perfusion effluent gave values of 1–4 µM ATP. Under this low ATP condition, replacement of external sodium and calcium causes the same drop in the calcium efflux. The same effect was observed at higher [Ca]i, (80 µM). These results suggest that the Na-Ca exchange component of the calcium efflux is apparently not dependent on the amounts of ATP in the axoplasm. Axons previously depleted of ATP show a significant transient drop in the calcium efflux when ATP is added to the dialysis medium. This effect probably represents the sequestering of calcium by the mitochondrial system. The consumption of calcium by the mitochondria of the axoplasm in dialyzed axons was determined to be of the order of 6.0 x 10-7 mol Ca++/mg of protein with an initial rate of 2.6 x 10-8 mol Ca++/min·mg of protein. Axons dialyzed with 2 mM cyanide after 8–10-min delays show a rise in the calcium efflux in the presence of "normal" amounts of exogenous ATP. This effect seems to indicate that cyanide, per se, can release calcium ions from internal sources.

scholarly journals Hemoglobin Charge Dependence on Hemoglobin Concentration in Vitro

1971 ◽  
Vol 57 (3) ◽  
pp. 283-289 ◽  
Author(s):  
C. M. Gary-Bobo ◽  
A. K. Solomon
Keyword(s):  
External Solution ◽  
Hemoglobin Concentration ◽  
Bulk Water ◽  
Red Cells ◽  
A Value ◽  
Charge Dependence ◽  
Hemoglobin Molecule ◽  
Sigmoid Curve ◽  
Human Red Cells

Studies have been made of the dependence of the charge of the hemoglobin molecule on hemoglobin concentration in the concentration range between 3 and 11 mmolal. The charge has been determined by measuring the distribution of 42K between a hemoglobin solution in a cellophane bag and an external solution. The pH was 6.6, the K concentration was 10 mM, and the temperature was 4°C. The charge decreased along a sigmoid curve from a value of +3 in the most dilute solutions to a value of +0.5 in the most concentrated solutions. The results were in excellent agreement with earlier studies of Gary-Bobo and Solomon in which Cl distribution was measured between human red cells and external solutions and thus give added support to the conclusion that the apparent anomalous osmotic behavior of human red cells may be attributed to concentration-dependent changes in the hemoglobin net charge. The present findings also support the view that the water in the red cell is solvent water for K and Cl and differs in no quantitatively important respect from bulk water in free solution.

Phosphofructokinase and glucose catabolism of Mucor and Penicillium species

1977 ◽  
Vol 23 (9) ◽  
pp. 1214-1224 ◽  
Author(s):  
V. Boonsaeng ◽  
P. A. Sullivan ◽  
M. G. Shepherd
Keyword(s):  
Pyruvate Kinase ◽  
Tricarboxylic Acid Cycle ◽  
Relative Rate ◽  
Pentose Phosphate ◽  
Kinetic Characteristics ◽  
Mucor Rouxii ◽  
Penicillium Species ◽  
Atp Inhibition ◽  
Cooperative Kinetics ◽  
Slight Inhibition

The primary catabolic pathways in the fungi Penicillium notation and P. duponti, and Mucor rouxii and M. miehei were examined by measuring the relative rate of 14CO2 production from different carbon atoms of specifically labelled glucose. It was found that these organisms dissimilate glucose predominantly via the Embden–Meyerhof pathway in conjunction with the tricarboxylic acid cycle and to a lesser extent by the pentose phosphate pathway.Phosphofructokinase (EC 2.7.1.11) activity could not be detected initially in Penicillium species because of the interference from mannitol-1-phosphate dehydrogenase (EC 1.1.1.17) and N ADH oxidase (EC 1.6.99.3). A combination of differential centrifuging and a heat treatment of Penicillium cell-free extracts in the presence of fructose-6-phosphate removed the interfering enzymes.The kinetic characteristics of phosphofructokinase from P. notatum and M. rouxii are described. The enzyme presents highly cooperative kinetics for fructose-6-phosphate. The kinetics for ATP show no cooperativity and inhibition by excess ATP is observed. The addition of AMP activated the P. notatum enzyme, relieving ATP inhibition; slight inhibition by AMP was observed with the M. rouxii enzyme. In contrast M. rouxii pyruvate kinase (EC 2.7.1.40) is activated 50-fold by fructose-1,6-diphosphate whereas pyruvate kinase from P. notatum and P. duponti were unaffected by fructose-1,6-diphosphate.

scholarly journals Calcium Efflux from Barnacle Muscle Fibers

1974 ◽  
Vol 63 (2) ◽  
pp. 144-167 ◽  
Author(s):  
J. M. Russell ◽  
M. P. Blaustein
Keyword(s):  
Large Fraction ◽  
Muscle Fibers ◽  
Electrochemical Gradient ◽  
Calcium Efflux ◽  
Barnacle Muscle ◽  
Sufficient Energy ◽  
Complex Models ◽  
Na Ions ◽  
45Ca Efflux ◽  
Barnacle Muscle Fibers

Calcium-45 was injected into single giant barnacle muscle fibers, and the rate of efflux was measured under a variety of conditions. The rate constant (k) for 45Ca efflux into standard seawater averaged 17 x 10–4 min–1 which corresponds to an efflux of about 1–2 pmol/cm2·s. Removal of external Ca (Cao) reduced the efflux by 50%. In most fibers about 40% of the 45Ca efflux into Ca-free seawater was dependent on external Na (Nao); treatment with 3.5 mM caffeine increased the magnitude of the Nao-dependent efflux. In a few fibers removal of Nao, in the absence of Cao, either had no effect or increased k; caffeine (2–3.5 mM) unmasked an Nao-dependent efflux in these fibers. The Nao-dependent Ca efflux had a Q10 of about 3.7. The data are consistent with the idea that a large fraction of the Ca efflux may be carrier-mediated, and may involve both Ca-Ca and Na-Ca counterflow. The relation between the Nao-dependent Ca efflux and the external Na concentration is sigmoid, and suggests that two, or more likely three, external Na+ ions may activate the efflux of one Ca+2. With a three-for-one Na-Ca exchange, the Na electrochemical gradient may be able to supply sufficient energy to maintain the Ca gradient in these fibers. Other, more complex models are not excluded, however, and may be required to explain some puzzling features of the Ca efflux such as the variable Nao-dependence.

scholarly journals Estimation of the free [Ca2+] gradient across endoplasmic reticulum membranes by a null-point method

1995 ◽  
Vol 310 (2) ◽  
pp. 371-374 ◽  
Author(s):  
A P Dawson ◽  
G T Rich ◽  
J W Loomis-Husselbee
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
External Medium ◽  
Microsomal Protein ◽  
Null Point ◽  
Similar Technique ◽  
Electrochemical Gradient ◽  
Efflux Rate ◽  
L1210 Cells ◽  
A Value

The rate of unidirectional efflux of 45Ca from rat liver microsomal vesicles loaded with 45Ca and then treated with thapsigargin is not inhibited by increased [Ca2+] in the external medium, although the net efflux rate is substantially inhibited. We have used this property to measure the electrochemical gradient of Ca2+ from the inside to the outside of the vesicles at a series of Ca2+ loadings, by measuring the external [Ca2+]free at which there is zero net efflux. At a loading of 7.9 +/- 0.6 nmol/mg of microsomal protein, the apparent internal [Ca2+]free is 21 +/- 1.6 microM. As the loading is increased, the internal [Ca2+]free increases linearly up to a value of 47 +/- 3.6 microM at a loading of 21.6 +/- 1.6 nmol/mg. Using a similar technique, the value for [Ca2+]free in the endoplasmic reticulum of permeabilized L1210 cells was found to be 12.5 microM.

Angiotensin-mediated calcium efflux from adrenal glomerulosa cells

1983 ◽  
Vol 245 (3) ◽  
pp. E281-E287 ◽  
Author(s):  
R. Foster ◽  
H. Rasmussen
Keyword(s):  
Angiotensin Ii ◽  
Calcium Uptake ◽  
Initial Increase ◽  
Calcium Efflux ◽  
Aldosterone Secretion ◽  
Precise Location ◽  
A Value ◽  
Aldosterone Production ◽  
Flow Through ◽  
Glomerulosa Cells

The effects of angiotensin II on efflux of radiocalcium and production of aldosterone from dispersed bovine adrenal glomerulosa cells were studied using a flow-through system. Concentrations of angiotensin II between 1.25 X 10(-10) and 1.25 X 10(-8) M were found to stimulate both radiocalcium efflux and the rate of aldosterone production. The increase in radiocalcium efflux occurred within 1.5-2.5 min after angiotensin addition, reached a peak in 3.0-4.5 min, and then declined to a value slightly greater than control. The initial increase in aldosterone production occurred 3-5 min after the peak of calcium efflux. In cells preloaded with [45Ca] and then perfused for 1 h with a medium containing no calcium, the basal rate of aldosterone production fell to zero. Angiotensin II (1.25 X 10(-8) M) caused no increase in aldosterone secretion rate but still caused an efflux of radiocalcium. Exposure of cells to 5 X 10(-5) M verapamil blocked the effect of 1.25 X 10(-10) M angiotensin on both radiocalcium efflux and aldosterone production, but only partially blocked the effects of 1.25 X 10(-8) M angiotensin. In addition to stimulating calcium uptake into adrenal glomerulosa cells, angiotensin II stimulates the mobilization of calcium from an intracellular pool. The precise location of this pool is not known.

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