Neuronal plasma membrane

There is one last, important point. The unequal distribution of ions across the plasma membrane of the neuron leads to a net negative charge on the inside of the neuron and a net positive charge on the outside. This separation of charge creates a potential difference, or voltage, across the neuronal plasma membrane. For a neuron at rest, this potential difference amounts to about 65 millivolts (mV), with the inside negative. By convention, we say that the resting potential of the neuron is -65 mV. 

In sum, the natural tendency will be for sodium, calcium, and chloride ions to flow into the neuron and for potassium ions to flow out, and in so doing to reduce the membrane potential to zero. In reality, this is not so easy. The plasma membrane of the neuron is not very permeable to these ions. If it were, it would be impossible to sustain concentration gradients across it. The rate of passive diffusion of these ions across this membrane is very slow, though not zero, and different for each ion. So how do ions get across the neuronal plasma membrane rapidly There are two ways gated channels and active transport by pumps. 

This conclusion is supported by the mechaiusm of action of imipramine. Once a neurotransmitter has been released into the synapse, there are two ways to terminate its action. The first is to degrade it to inactive products, by MAO for example. The second is to remove the neurotransmitter through reuptake into the presynaptic neuron. This mechaiusm is the predominant one for clearing the synapse of serotonin, norepinephrine, and dopamine. Specific proteins embedded in the neuronal plasma membrane mediate the reuptake of these monoamine neurotransmitters. Imipramine is a nonspecific monoamine reuptake inhibitor that is, it slows the reuptake of aU three of these monoamines, which enhances the activity of these neurotransmitters. This also suggests that a deficit in the activity of one or more of the monoamines underlies the problem of depression. 

Thomzig, A., Wenzel, M., Karschin, C., Eaton, M. J., Skatchkov, S. N., Karschin, A., Veh, R. W. Kir6.1 is the principal pore-forming subunit of astrocyte but not neuronal plasma membrane K-ATP channels, Molecular and Cellular Neuroscience 2001, 18, 671-690. 

Neurons oxidize glucose by glycolysis and the citric acid cycle, and the flow of electrons from these oxidations through the respiratory chain provides almost all the ATP used by these cells. Energy is required to create and maintain an electrical potential across the neuronal plasma membrane. The membrane contains an electrogenic ATP-driven antiporter, the Na+K+ ATPase, which simultaneously pumps 2 K+ ions into and 3 Na+ ions out of the neuron (see Fig. 11-37). The resulting... 

C. Wu, S. Butz, Y. Ying and R. G. W. Anderson, Tyrosine kinase receptors concentrated in caveolae-like domains from neuronal plasma membrane. J Biol Chem 272,3554-3559 (1997). 

Synaptosomes can be subfractionated into a heavy membrane fraction that contains plasma membranes, synaptic vesicle clusters and most of the contaminating membranes, a light membrane fraction that is enriched in synaptic vesicles and devoid of measurable contamination by mitochondria or neuronal plasma membranes, and a... 

Neurons in the central nervous system communicate by chemical transmission. Of relevance to the present discussion are monoamine neurons that release dopamine, norepinephrine, or serotonin as one of their transmitters in response to an action potential. Reuptake transporter proteins embedded in the neuronal plasma membrane then clear the synapse of monoamines, typically taking up 70-80%) of the released transmitter. This reuptake is thought to be the major termination mechanism for the monoamine chemical signaling process. 

Shi R, Qiao X, Emerson N, Malcom A (2001) Dimethylsulfoxide enhances CNS neuronal plasma membrane resealing after injury in low temperature or low calcimn. J Neurocytol 30(9-10) 829-839... 

Calcium channels (Cay channels) mediate calcium influx in neuronal cells in response to membrane depolarisation, mediating a wide range of intracellular processes such as activation of calcium-dependent enzymes, gene transcription, and neurotransmitter exocytosis/secretion. Their activity is an essential requirement for the coupling of electric signals in the neuronal plasma membrane to physiological events within the cells. Biochemical characterisation of native brain Cay channels revealed that, in addition to the large principal... 

A EXPERIMENTAL FIGURE 7-34 Probability of channel opening and current flux through individual voltage-gated K" channels increases with the extent of membrane depolarization. These patch-clamp tracings were obtained from patches of neuronal plasma membrane clamped at three different potentials, +50, +20, and -10 mV. The upward deviations in the current indicate the opening of channels and movement of... 

A FIGURE 14-30 Proteolytic cleavage of APP, a neuronal plasma membrane protein. (Left) Sequential proteolytic cleavage by a-secretase (step ) and y-secretase (step B) produces an innocuous membrane-embedded peptide of 26 amino acids. y-Secretase is a complex of several proteins, but the proteolytic site that catalyzes intramembrane cleavage probably resides within presenilin 1. Right) Cleavage in the... 

About 80% of the energy produced in the brain is consumed by neurons, which constitute only 10% of all brain cells. Such large amounts of energy are indispensable for the maintenance and restoration of neuronal plasma membrane potentials (of several Hz frequency) during events linked to neurotransmission. 

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