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Currents across cell membranes

The transmembrane potential of cardiac cells is determined by the concentrations of several ions—chiefly sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)—on either side of the membrane and the permeability of the membrane to each ion. These water-soluble ions are unable to freely diffuse across the lipid cell membrane in response to their electrical and concentration gradients they require aqueous channels (specific pore-forming proteins) for such diffusion. Thus, ions move across cell membranes in response to their gradients only at specific times during the cardiac cycle when these ion channels are open. The movements of the ions produce currents that form the basis of the cardiac action potential. Individual channels are relatively ion-specific, and the flux of ions through them is... [Pg.272]

Like all caldum channel blodcers, verapamil modulates ionic calcium influx across cell membranes of conductile and contractile myocardial cells, as well as arterial smooth muscle. The modulation of calcium influx slows atrioventricular conduction, reduces myocardial contractility and systemic vascular resistance, and results in coronary and peripheral vaso dilation. Verapamil is currently indicated for controlling angina, hypertension, paroxysmal supraventricular tachycardia, and rapid ventricular atrial flutter or fibrillation (1-5),... [Pg.315]

In 1952 Hodgkin and Huxley (3) proposed a mathematical form that could represent the currents measured across cell membranes. They noted (3) that these equations can be given a physical basis if we assume that potassium can only cross the membrane when four similar particles occupy a certain region of the membrane. .. and if the sodium conductance is assumed to be proportional to the number of sites on the inside of the membrane which are... [Pg.355]

The electrophysiological voltage clamp technique is a widely used method to approach mechanisms of ion transport across cell membranes. Basically, the voltage clamp is the application of a rectangular electric field and the measurement of relaxations of electric currents which are frequently rate-controlled by structural changes in the ion transport gating proteins. In a similar manner chemical relaxtion kinetics appears to be the method of... [Pg.133]

The data showed that, with the membrane voltage held constant, the current across the membrane displays nonlinear characteristics during stimulation. These findings seem to be crucial in explanation of the phenomenon of electrical behavior of the artificial proteinoid cell, as the negative resistance is a necessary characteristic for the generation of the oscillations observed. [Pg.389]

As an example, we consider the oldest and most powerful method for single-molecule kinetic analysis, the patch clamp analysis of ion-channel proteins. Ion channels regulate the flow of simple ions such as Na, K, and Ca across cell membranes. Movement of ions is equivalent to electrical current, and we have very sensitive methods for detecting electrical currents. If we take a small glass pipette and insert it into a membrane just right, we can electrically insulate the patch of membrane inside the pipette from the rest of the world. If done properly, a single ion channel will be in the patch, and we can watch... [Pg.360]

For electrode (conductor/semiconductor) surfaces, mass transport can be controlled with a variety of experimental protocols and the interfacial flux is measured directly via the current response (measured as a function of potential, time, etc.) [1], This is not true of other interfaces, such as minerals and many biomimetic surfaces in contact with the solution. In these instances, fluxes have often been deduced in a convoluted time- and space-averaged manner by determining the accumulation/loss of material in a bulk phase as a function of time. This leads to a considerable loss of dynamic resolution. Furthermore, in some systems, mass transport between the bulk and the interface is difficult to estimate, leading to incorrect mechanistic interpretation, with major implications for practical applications, whether this concerns drug transport across cell membranes or the growth of crystals. [Pg.418]

The other intracellular voltammetric method worked out is applicable for measurement of transport rates across cell membranes. For this the cell is attached on gold substrate. The working electrode is positioned inside the cell over the section of the membrane which adheres to the gold surface. The regeneration of the mediator at the gold surface is faster and less complicated. Therefore the positive feedback current is less affected by a slow intracellular redox reaction that can be the case if the transport rate is tested by extracellular voltammetry. [Pg.322]

With eveiy change in ion concentration, there is an electrical effect generated by an electrochemical cell. The anion membrane shown in the middle has three cells associated with it, two caused by the concentration differences in the boundaiy layers, and one resulting from the concentration difference across the membrane. In addition, there are ohmic resistances for each step, resulting from the E/I resistance through the solution, boundary layers, and the membrane. In solution, current is carried by ions, and their movement produces a fric tion effect manifested as a resistance. In practical applications, I R losses are more important than the power required to move ions to a compartment wim a higher concentration. [Pg.2030]

Fig. 5. Tentative mixed potential model for the sodium-potassium pump in biological membranes the vertical lines symbolyze the surface of the ATP-ase and at the same time the ordinate of the virtual current-voltage curves on either side resulting in different Evans-diagrams. The scale of the absolute potential difference between the ATP-ase and the solution phase is indicated in the upper left comer of the figure. On each side of the enzyme a mixed potential (= circle) between Na+, K+ and also other ions (i.e. Ca2+ ) is established, resulting in a transmembrane potential of around — 60 mV. This number is not essential it is also possible that this value is established by a passive diffusion of mainly K+-ions out of the cell at a different location. This would mean that the electric field across the cell-membranes is not uniformly distributed. Fig. 5. Tentative mixed potential model for the sodium-potassium pump in biological membranes the vertical lines symbolyze the surface of the ATP-ase and at the same time the ordinate of the virtual current-voltage curves on either side resulting in different Evans-diagrams. The scale of the absolute potential difference between the ATP-ase and the solution phase is indicated in the upper left comer of the figure. On each side of the enzyme a mixed potential (= circle) between Na+, K+ and also other ions (i.e. Ca2+ ) is established, resulting in a transmembrane potential of around — 60 mV. This number is not essential it is also possible that this value is established by a passive diffusion of mainly K+-ions out of the cell at a different location. This would mean that the electric field across the cell-membranes is not uniformly distributed.

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Currents across cell membranes Hodgkin-Huxley

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