Excitable cells regulation

Pasti L, Zonta M, Pozzan T, Vicini S, Carmignoto G (2001) Cytosolic calcium oscillations in astrocytes may regulate exocytotic release of glutamate. J Neurosci 21 477 84 Fenner R, Neher E (1988) The role of calcium in stimulus-secretion coupling in excitable and non-excitable cells. J Exp Biol 139 329-345... 

In previous reviews on this matter by Gogelein [9] and myself [10] it has been pointed out that the Cl -channels of the central nervous system and of skeletal muscle are distinct from those of non-excitable cells. The latter entity is in itself obviously heterogeneous with respect to its occurrence and function. In apolar as well as in polarized cells Cl -channels may be involved in volume regulation. As a simple rule gating of K" - and Cl -channels is likely to occur whenever cell volume has to be down-regulated [11], as is the case in regulatory volume decrease of cell volume. A simple means to induce this phenomena is the exposure of cells to hypoosmolar solutions [12]. For example Cl -channels play an important role in... 

Capacitative Ca2+ entry is the predominant mode of regulated Ca2+ entry in nonexcitable cells but it also occurs in a number of excitable cell types. This pathway of Ca2+ entry is usually associated with the activation of phospholipase C, which mediates the formation of IP3 (see Ch. 20). Intracellular application of IP3 mimics the ability of hormones and neurotransmitters to activate calcium ion entry, and activation of calcium ion entry by hormones and neurotransmitters can be blocked by intracellular application of low-molecular-weight heparin, which potently antagonizes IP3 binding to its receptor. There is considerable evidence for the presence of an IP3 receptor in the plasma membrane of some cells types. 1(1,3,4,5)P4, a product of IP3 phosphorylation, has been shown in some cells to augment this action of IP3 in activating PM calcium ion entry, but in others IP3 alone is clearly sufficient. 

A test for the sensitivity of a fluorimeter is to measure the intensity of fluorescence of the Raman diffusion peak of a cell filled with water and with an optical pathlength of 1 cm. If the wavelength of excitation is regulated to 250 nm, at which wavelength must the measurement be made (the Raman displacement of water is 3 380 cm-1) ... 

Normal cellular physiology depends on the ability of ions to move across cell membranes. Ion channels are highly specialized transport proteins that facilitate this movement by forming regulated ion-permeable routes through the membranes of nearly all excitable and non-excitable cells. They are found in plasma membranes and in the membranes of intracellular organelles. Plasma membrane ion channels display significant structural and functional diversity (Ashcroft 2006) and... 

Calcium performs a variety of cellular functions in muscle and nerve that ultimately result in muscular contraction. Excellent descriptions of calcium s function in muscle and nerve are to be found in the reviews by Hoyle (37), Cohen (38), and Robertson (39). At the neuromuscular junction, the excitable cells are very sensitive to changes in extracellular concentrations of calcium. Curtis (40) and Luttgau (41) described a fall in the resting action potential and electrical resistance when the extracellular calcium concentration fell below 10 M. The action potential and electrical resistance returned to normal following addition of calcium to this vitro preparation. The magnitude of the Initial muscle membrane action potential, that which regulates the propagation of further muscle contraction, is also mediated by the extracellular calcium concentration. While the inward flow of sodium ions from the extracellular space remains the dominant factor in the mechanism of muscle membrane depolarization, calcium ion flux appears to mediate the cell s permeability to sodium ions. This effect is particularly true in cardiac tissue (W). 

Calcium has a dual role in the regulation of cell function It carries charge and thus contributes to the changes of membrane potential in excitable cells, and it acts as a biochemical messenger by directly binding to proteins and modifying their functional state. Proteins directly or indirectly affected by calcium are very diverse and include enz mies, cy-toskeletal proteins, ion channels, and transcription factors. 

Ion channels are essential for a wide range of functions such as neurotransmitters secretion and muscle contraction. Ion channels mediate Na, Ca +, and Cl conductance induced by membrane potential changes. These channels propagate action potentials in excitable cells and are also involved in the regulation of membrane potential and intracellular Ca + transients in most eukaryotic cells. About 300 genes code for subunits of voltage-gated ion channels. 

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