Physiology

The membrane of astrocytes contains a variety of neurotransmitter transporters, ion channels, and gap junctions. The neurotransmitter transporters act to clear the ECS of neurotransmitters, which accumulate during electrical activity. The continued presence of neurotransmitters in the ECS could lead to cell death by increased intracellular Ca2 + , e.g., glutamate. Alternatively, the sustained presence of GABA may lead to prolonged inhibition of cells. Astrocytes also contain a variety of ion channels. Although Na + channels are present, they are not present in sufficient density relative to K+ channels to cause action potentials. Multiple K+ channels are present and because astrocytes are almost exclusively permeable to K+ at rest, they act as K+ electrodes and the resting membrane potential is dictated almost exclusively by the transmembrane concentration of K+ ions. As such, astrocytes are exquisitely sensitive to changes in extracellular K+ concentration, and changes in this concentration due to increased neuronal activity are immediately sensed by astrocytes. Astrocytes also contain Ca2+ channels, but there has been controversy about whether Ca2 + channels are present in vivo. In cultured astrocytes and in astrocytes studied after having undergone trauma, Ca2+ channels have been shown to be present. However, one study could find no evidence of Ca2 + channels present in vitro, suggesting instead that increased intracellular Ca2 + occurred due to the activation of metabotropic glutamate receptors. These data suggested that the presence of Ca2+ channels in previous studies was due to up-regulation of Ca2+ channel expression induced by culture conditions or injury. However, technical limitations have made answering this question difficult. Patch clamp recordings suffer from the effects ofspace clamp induced by the gap junctional dissipation of current. However, a study using electrophysiological techniques and antibodies directed at Ca2+ channel subunits indicated that nifedipine-sensitive L-type Ca2+ channels are present on both astrocytes and axons in the adult rat optic nerve.

Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

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