Читать книгу Neurobiology For Dummies - Frank Amthor - Страница 100

Besides the sodium-potassium ion pump, other transporters exist that are also essential for different aspects of neural function. One is the sodium-calcium exchanger. The main function of the sodium-calcium exchanger is to remove calcium from the cytoplasm. (Calcium levels inside cells are usually held to levels of a few hundred nanomolar.) The sodium-calcium exchanger is found not only in the plasma membranes, but also in mitochondria and the endoplasmic reticulum of neurons. The sodium-calcium exchanger works by using the energy stored in the electrochemical gradient of sodium instead of chemical energy from ATP. The energy derived from three sodium ions flowing down this gradient brings in one calcium ion.

Another important class of transporters is the group of cation chloride co-transporters (sometimes called CCCs). Variants of these exchangers may bring in or push out chloride in exchange for potassium or potassium and sodium. Membrane transporters also exist for neurotransmitters such as glutamate, dopamine, serotonin, and norepinephrine. These transporters are involved in limiting synaptic transmission by scavenging neurotransmitters from the synaptic cleft, thereby recycling the neurotransmitter molecules. (Chapter 4 gets into the processes involved in neurotransmitter release.) In some special cases, transporters can also release neurotransmitters.