Potencial De Membrana Y Su Intercambio Iónico En Los Humanos.
Introducción.
Todas las células de nuestro organismo tienen una membrana celular que consiste de una doble capa de fosfolipidos y proteínas que permiten mantener una diferencia electrostática entre el interior de la célula y el exterior de la célula.
FIG.1
Esta diferencia de potencial a través de la membrana está dada por varios factores intra y extracelulares que mencionaremos más adelante. En reposo la célula presenta una carga negativa en su interior y una carga positiva en su exterior. A ese estado de diferencia de cargas se le llama potencial de membrana
FIG.2
Los Factores que intervienen para mantener esa diferencia de cargas a través de la membrana son:
1.- Permeabilidad selectiva de la membrana.
2.- Bomba de sodio y potasio
3.- Proteínas intracelulares de carga negativa.
La permeabilidad selectiva de la membrana consiste en que la membrana celular en reposo es impermeable al sodio (con mayor contenido el exterior de la célula) de tal manera que el sodio (de carga positiva) no entra en la célula y se concentra en el exterior de le célula, siendo el liquido extracelular de carga positiva. Lo contrario sucede con el potasio (de carga positiva), ya que la membrana celular es permeable al potasio (de carga positiva), ya que la membrana celular es permeable al potasio y cuando este ion ingresa al interior de la célula por acción de la bomba de sodio/potasio sale posteriormente por difusión pasiva al exterior de la célula de tal manera que se acumulan más iones positivos en el liquido extracelular. Sin embargo se mantiene siempre una mayor concentración de sodio en el exterior y de iones potasio en el interior de la célula, saliendo este ultimo ion al exterior por gradiente de concentración, Ver Imagen:
FIG.3
Que sucede cuando generamos un potencial de acción (lo contrario al potencial en reposo):
1.- Cambia la permeabilidad de la membrana: Se vuelve esta última permeable al sodio y semipermeable al potasio, de tal manera que ingresan iones positivos al interior de la célula (ion sodio) por gradiente de concentración y salen menos iones positivos al exterior de la célula y carga negativa en el exterior de la célula. Ver imagen:
FIG.4
Por ejemplo en el musculo cardiaco se genera una curva de potencial de acción que se registra en un osciloscopio de la siguiente manera:
FIG.5
Descripción de la curva:
La primera fase o fase 0 consiste en el ascenso de la curva y se debe a la entrada de sodio a la célula. La fase I (ligero descenso) a la entrada de cloro (ion negativo), la fase II a la entrada de calcio (meseta de la curva) y fase III a una salida progresiva de potasio que origina un descenso (salida de iones positivos) de la curva. Existe una fase IV que se produce por disminución de la salida de potasio al exterior de la celula. Ver imagen:
FIG.6
Este potencial de acción se puede iniciar y conducir a través de cualquier parte de la membrana celular y de esta manera por ejemplo, el sistema nervioso puede enviar señales eléctricas a distancia como podría ser la transmisión de dolor que inicia en un sitio de presión en la piel que contienen receptores del dolor hacia el cerebro. Ver Imagen:
FIG.7
Dr. Andrés Pascual García.
Cardiología- Neumología
Consulta médica en línea:
Membrane potential and Their Ion Exchange in Humans
Introduction
Every cell in our body have a cell membrane consisting of a double layer of phospholipids and proteins that help maintain an electrostatic difference between the interior of the cell and exterior of the cell.
FIG.1
This potential difference across the membrane is given by various intra-and extracellular factors mentioned below. At rest the cell has a negative charge inside and a positive charge on the outside. In this state of charge difference is called the membrane potential
FIG.2
Factors involved to keep this difference in charge across the membrane are:
1 .- Selective permeability of the membrane.
2 .- sodium and potassium pump
3 .- negatively charged intracellular proteins.
The selective permeability of the membrane is that the resting membrane is impermeable to sodium (more content outside the cell) so that the sodium (positively charged) is not within the cell and is concentrated on the outside of her cell, being positively charged extra-cellular fluid. The opposite happens with potassium (positively charged) as the cell membrane is permeable to potassium (positively charged) as the cell membrane is permeable to potassium and when this ion enters into the cell by action sodium pump / potassium out subsequently by passive diffusion outside the cell so that more positive ions accumulate in the extracellular fluid. However, it keeps a higher concentration of sodium in potassium ions outside and inside the cell, leaving the latter outside ion concentration gradient, see Image:
1 .- Selective permeability of the membrane.
2 .- sodium and potassium pump
3 .- negatively charged intracellular proteins.
The selective permeability of the membrane is that the resting membrane is impermeable to sodium (more content outside the cell) so that the sodium (positively charged) is not within the cell and is concentrated on the outside of her cell, being positively charged extra-cellular fluid. The opposite happens with potassium (positively charged) as the cell membrane is permeable to potassium (positively charged) as the cell membrane is permeable to potassium and when this ion enters into the cell by action sodium pump / potassium out subsequently by passive diffusion outside the cell so that more positive ions accumulate in the extracellular fluid. However, it keeps a higher concentration of sodium in potassium ions outside and inside the cell, leaving the latter outside ion concentration gradient, see Image:
FIG.3
What happens when we generate an action potential (as opposed to resting potential):
1 .- Change the permeability of the membrane: the latter was re-permeable semi-permeable sodium and potassium, so that positive ions enter into the cell (sodium ion) gradient of concentration and go out less positive ions outside Cell and negative charge on the outside of the cell. View image:
1 .- Change the permeability of the membrane: the latter was re-permeable semi-permeable sodium and potassium, so that positive ions enter into the cell (sodium ion) gradient of concentration and go out less positive ions outside Cell and negative charge on the outside of the cell. View image:
FIG.4
For example, in the heart muscle generates an action potential curve is recorded on an oscilloscope as follows:
FIG.5
Description of the curve:
The first phase or phase 0 is the rise of the curve and is due to the influx of sodium into the cell. Phase I (slight decrease) at the entrance of chlorine (negative ion), Phase II at the entrance of calcium (plateau of the curve) and phase III to a progressive output of potassium, which causes a decrease in output (positive ions) of the curve. There is a phase IV is caused by decreased outflow of potassium outside the cell. View image:
The first phase or phase 0 is the rise of the curve and is due to the influx of sodium into the cell. Phase I (slight decrease) at the entrance of chlorine (negative ion), Phase II at the entrance of calcium (plateau of the curve) and phase III to a progressive output of potassium, which causes a decrease in output (positive ions) of the curve. There is a phase IV is caused by decreased outflow of potassium outside the cell. View image:
FIG.6
This action potential can start and drive through any part of the cell membrane and thus for example, nerves can send electrical signals at a distance and could be the transmission of pain that starts in one place pressure on containing skin pain receptors to the brain. View Image:
FIG.7
Dr. Andrés Pascual García.
Cardiology- Neumology
Online Medical Consultation:
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