Voltage dependent sites

The PBRis distinct from the central BZ receptor although both can be present in the same tissues in differing ratios. PBRs are predominately localized on the outer mitochondrial membrane and are thus intracellular BZ recognition sites. The PBR is composed of three subunits an 18,000 mol wt subunit that binds isoquinoline carboxamide derivatives a 30,000 mol wt subunit that binds BZs and a 32,000 mol wt voltage-dependent anion channel subunit. The porphyrins may be endogenous ligands for the PBR. PBRs are involved in the control of cell proliferation and differentiation and steroidogenesis. 

When the required test voltage is not available at site, the reduced voltage power frequency withstand test may be carried out at still lower test voltages, depending upon the voltage availability at site. Then the duration of the test must be increased as shown in Table 14.8, and IS 10118-3 and BS 159. 

Choice of rated lighting impulse withstand voltage depends on exact site conditions and duties. 

In the previous section was given the experimental demonstration of two sites. Here the steady state scheme and equations necessary to calculate the single channel currents are given. The elemental rate constants are thereby defined and related to experimentally determinable rate constants. Eyring rate theory is then used to introduce the voltage dependence to these rate constants. Having identified the experimentally required quantities, these are then derived from nuclear magnetic resonance and dielectric relaxation studies on channel incorporated into lipid bilayers. 

Fig. 7. A. Kinetic scheme for two site single filing channel. Ten rate constants are required. In the absence of a transmembrane potential, however, the two-fold symmetry of the channel reduces this to five rate constants. Then Eyring rate theory is used to introduce the voltage dependence as shown in Eq. 6.

An increase in [Na+]j can also regulate the Na+/Ca2+ exchanger. In particular, when intracellular Na+ increases, it binds to the transport site of the exchanger molecule, and after this Na+ influx, an inactivation process of the exchanger occurs. This inactivation process, very similar to the phenomenon occurring in voltage-dependent ionic channels, is named... 

The acute toxicity of p,p -DDT to both vertebrates and invertebrates is attributed mainly to its action upon axonal Na+ channels, which are voltage dependent (see Figure 5.4 Eldefrawi and Eldefrawi 1990). The molecule binds reversibly to a site... 

This chapter summarizes recent work on the molecular basis of the toxic actions of ciguatoxin and brevetoxins. It is shown (i) that the molecular target for these toxins is the voltage-dependent Na channel of excitable tissues arid (ii) that ciguatoxin and brevetoxins share a common receptor site on the Na channel. 

The polypeptide toxins from the scorpions Centruroides suffusus and Tityus ser-rulatus. These toxins act by shifting the voltage dependence of the activation of Na channels, thereby inducing a Na channel activity at negative potentials at which Na channels are normally closed 63,64). Site 4 toxins, because of their high affinity for the Na channel, have been efficient tools to elucidate the molecular structure of the Na channel 30,65,66). 

Joseph-Iiauzun, E., Farges, R., Delmas, P., Ferrara, P. Loison, G. (1997). The Mr 18,000 subunit of the peripheral-type benzodiazepine receptor exhibits both benzodiazepine and isoquinoline carboxamide binding sites in the absence of the voltage-dependent anion channel or of the adenine nucleotide carrier. J. Biol. Chem. 272, 28102-6. 

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