Sodium dependence of carnitine transport in isolated perfused adult rat hearts

1983 ◽  
Vol 244 (2) ◽  
pp. H247-H252 ◽  
Author(s):  
T. C. Vary ◽  
J. R. Neely
Keyword(s):  
Potassium Concentration ◽  
Sodium Concentration ◽  
Extracellular Potassium ◽  
Extracellular Potassium Concentration ◽  
Rat Hearts ◽  
Carrier Mediated Transport ◽  
Physiological Serum ◽  
Carnitine Transport ◽  
Extracellular Sodium ◽  
Carnitine Concentration

In heart muscle, the intracellular carnitine concentration is approximately 40 times higher than the plasma carnitine concentration, suggesting the existence of an active transport process. At physiological serum carnitine concentrations (44 microM), 80% of total myocardial carnitine uptake occurs via a carrier-mediated transport system. The mechanism of this carrier-mediated transport was studied in isolated perfused rat hearts. Carnitine transport showed an absolute dependence on the extracellular sodium concentration. The rate of carnitine transport was linearly related to the perfusate sodium concentration at every perfusate carnitine concentration examined (15-100 microM). Total removal of extracellular sodium completely abolished the carrier-mediated transport. Decreasing the perfusate potassium concentration from a control of 5.9 to 0.6 mM stimulated transport by 35%, whereas increasing the extracellular potassium concentration from 5.9 to 25 mM reduced transport by 60%. The carrier-mediated transport was inversely proportional to the extracellular potassium concentration. Acetylcholine (10(-3) M), isoproterenol (10(-7) M), or ouabain (10(-3) did not alter the rate of carnitine transport. Addition of tetrodotoxin (10(-5) stimulated carnitine transport by about 40%, while gramicidin S (5 X 10(-6) M) decreased uptake by about 18% relative to control. The data provide evidence that carnitine transport by cardiac cells occurs by a Na+-dependent cotransport mechanism that is dependent on the Na+ electrochemical gradient.

scholarly journals Untersuchungen über den Kaliumtransport bei Escherichia coli B / Potassium Transport in Escherichia coli B

1972 ◽  
Vol 27 (1) ◽  
pp. 62-67 ◽  
Author(s):  
G. Pilwat ◽  
U. Zimmermann
Keyword(s):  
Escherichia Coli ◽  
Potassium Concentration ◽  
Sodium Concentration ◽  
Extracellular Potassium ◽  
High Sodium ◽  
Extracellular Potassium Concentration ◽  
Intracellular Potassium ◽  
Extracellular Sodium ◽  
Escherichia Coli B ◽  
Intracellular Potassium Concentration

The stationary intracellular potassium concentration in E. coli B 525 has been studied as a function of the extracellular potassium and sodium concentrations.The ratio of extracellular to intracellular potassium concentration is shown to be a linear function of the extracellular potassium concentration if the extracellular sodium concentration is low (20 mmoles/l). In the case of high sodium concentration (100 mmoles/l) the ratio is independent of the extracellular potassium concentration if the potassium concentration is below 1,2 mmoles/l.In order to describe the distribution of potassium uniformly over the whole range of the extracellular potassium and sodium concentrations a carrier system with two sites has to be supposed.

scholarly journals The Ionic Basis of Electrical Activity in Embryonic Cardiac Muscle

1968 ◽  
Vol 52 (3) ◽  
pp. 666-681 ◽  
Author(s):  
Billy K. Yeh ◽  
Brian F. Hoffman
Keyword(s):  
Electrical Activity ◽  
Sodium Concentration ◽  
Cardiac Cells ◽  
Resting Potential ◽  
Extracellular Potassium ◽  
Embryonic Chick ◽  
Extracellular Potassium Concentration ◽  
Chick Heart ◽  
Extracellular Sodium ◽  
Ionic Basis

The intracellular sodium concentration reported for young, embryonic chick hearts is extremely high and decreases progressively throughout the embryonic period, reaching a value of 43 mM immediately before hatching. This observation suggested that the ionic basis for excitation in embryonic chick heart may differ from that responsible for electrical activity of the adult organ. This hypothesis was tested by recording transmembrane resting and action potentials on hearts isolated from 6-day and 19-day chick embryos and varying the extracellular sodium and potassium concentrations. The results show that for both young and old embryonic cardiac cells the resting potential depends primarily on the extracellular potassium concentration and the amplitude and rate of rise of the action potential depend primarily on the extracellular sodium concentration.

scholarly journals The Ionic Basis of Electrical Activity in Embryonic Cardiac Muscle

1968 ◽  
Vol 52 (4) ◽  
pp. 666-681 ◽  
Author(s):  
Billy K. Yeh ◽  
Brian F. Hoffman
Keyword(s):  
Electrical Activity ◽  
Sodium Concentration ◽  
Cardiac Cells ◽  
Resting Potential ◽  
Extracellular Potassium ◽  
Embryonic Chick ◽  
Extracellular Potassium Concentration ◽  
Chick Heart ◽  
Extracellular Sodium ◽  
Ionic Basis

The intracellular sodium concentration reported for young, embryonic chick hearts is extremely high and decreases progressively throughout the embryonic period, reaching a value of 43 mM immediately before hatching. This observation suggested that the ionic basis for excitation in embryonic chick heart may differ from that responsible for electrical activity of the adult organ. This hypothesis was tested by recording transmembrane resting and action potentials on hearts isolated from 6-day and 19-day chick embryos and varying the extracellular sodium and potassium concentrations. The results show that for both young and old embryonic cardiac cells the resting potential depends primarily on the extracellular potassium concentration and the amplitude and rate of rise of the action potential depend primarily on the extracellular sodium concentration.

Disorders of potassium homeostasis

2010 ◽  
pp. 3831-3845 ◽  
Author(s):  
J Firth
Keyword(s):  
Membrane Potential ◽  
Potassium Concentration ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Normal Range ◽  
Critical Determinant ◽  
Potassium Homeostasis ◽  
Extracellular Potassium Concentration

The normal range of potassium concentration in serum is 3.5 to 5.0 mmol/litre and within cells it is 150 to 160 mmol/litre, the ratio of intracellular to extracellular potassium concentration being a critical determinant of cellular resting membrane potential and thereby of the function of excitable tissues....

Theoretical analysis of parameters leading to frequency modulation along an inhomogeneous axon

1976 ◽  
Vol 39 (4) ◽  
pp. 909-923 ◽  
Author(s):  
I. Parnas ◽  
S. Hochstein ◽  
H. Parnas
Keyword(s):  
Potassium Concentration ◽  
Single Step ◽  
Repetitive Firing ◽  
Extracellular Potassium ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Extracellular Potassium Concentration ◽  
Spike Shape ◽  
Single Spike ◽  
Low Pass

1. Theoretical computations were conducted on a computer model of a segmented, nonhomogeneous axon to understand the mechanism of frequency block of conduction. 2. The model is based on the Hodgkin-Huxley equations modified in several ways to better describe the cockroach axon. We used cockroach parameters where available. 3. The increase in fiber radius was spread over a series of segments to approximate a taper. We found that a taper allows a larger overall increase in fiber diameter than a single step to be successfully passed. 4. We studied effects on a train of impulses. The modified equations included effects due to changes in extracellular potassium concentration resulting from the repetitive firing of the axon. 5. An increase in diameter which allows a single spike to pass blocks the subsequent impulses in a train at the taper if potassium concentration variability is introduced. This could explain the low-pass filter characteristics of axon constrictions. 6. Results of the model fit well with the experiemental spike shape and height. Data were computed for the refractory period and its dependence on the taper parameters.

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