Calcium conductivity cells

Macdonald, R. L., Skerritt, J. H., Werz, M. A. Adenosine agonists reduce voltage-dependent calcium conductance of mouse sensory neurones in cell culture, J. Physiol. 1986, 370, 75-90. 

Fig. 2.9 Two-dimensional bifurcation diagram outlining the main bifurcation structure for the /3-cell model in the (Vs, ks) parameter plane. Notice the squid-shaped black region with chaotic dynamics. Vs characterizes the voltage dependence of the gating variable for the calcium conductance, and k is a measure of the ratio of the fast and the slow time scales.

Cepeda C, Colwell CS, Itri JN, Chandler SH, Levine MS (1998) Dopaminergic modulation of NMDA-induced whole cell currents in neostriatal neurons in slices contribution of calcium conductances. J Neurophysiol 79 82-94. 

Phenytoin is a hydantoin derivative like dantrolene and the oldest non-sedative anticonvulsant drug known. It alters sodium, potassium and calcium conductance across cell membranes thereby altering membrane potentials and amino acid and neurotransmitter concentrations (i.e. norepinephrine (noradrenaline), acetylcholine and GABA). Its major mode of action appears to be the blockade of sodium channels and e inhibition of the generation of repetitive action potentials (membrane stabilization) (see Chs 9 and 12). 

In another article, Wang et al. (1993) used the CVCC conductivity cell for measurement of a variety of molten cryolite melts with additives of aluminum fluoride, aluminum oxide, calcium fluoride, magnesium fluoride, and lithium fluoride. On the basis of the measured results, a multiple regression equation for the electrical conductivity of cryolite melts was derived. Influence of the bath composition on the electrical conductivity at different bath temperatures was discussed. A comparison of the measured results with the published electrical conductivity values for cryolite melts was made. The new regression equation can be used to calculate electrical conductivity of cryolite melts in modern industrial bath chemistry. 

Not all cells in the cardiac conduction system rely on sodium influx for initial depolarization. Some tissues depolarize in response to a slower inward ionic current caused by calcium influx. These calcium-dependent tissues are found primarily in the SA and AV nodes (both L- and T-channels) and possess distinct conduction properties in comparison with the sodium-dependent fibers. Calcium-dependent cells generally have a less negative RMP (-40 to -60 mV) and a slower conduction velocity. Furthermore, in calcium-dependent tissues, recovery of excitability outlasts full repolarization, whereas in sodium-dependent tissues, recovery is prompt after repolarization. These two types of electrical fibers also differ dramatically in how drugs modify their conduction properties (see below). 

Negative chronotropic and dromotropic effects. ACh acts to decrease the rate of spontaneous depolarization of the cells of the SA node, decreasing heart rate. It also acts to decrease the rate of conduction through the atrioventricular (AV) node, through changes in sodium and calcium conductance. 

Fish, R.D., Sperti, G., Colucci, W.S., and Clapham, D.E. (1988) Phorbol ester increases the dihydropyridine-sensitive calcium conductance in a vascular smooth muscle cell line. Circulation Research, 62 1049-1054. 

Disease States. Rickets is the most common disease associated with vitamin D deficiency. Many other disease states have been shown to be related to vitamin D. These can iavolve a lack of the vitamin, deficient synthesis of the metaboUtes from the vitamin, deficient control mechanisms, or defective organ receptors. The control of calcium and phosphoms is essential ia the maintenance of normal cellular biochemistry, eg, muscle contraction, nerve conduction, and enzyme function. The vitamin D metaboUtes also have a function ia cell proliferation. They iateract with other factors and receptors to regulate gene transcription. 

Verapamil (Table 1), the first slow channel calcium blocker synthesized to selectively inhibit the transmembrane influx of calcium ions into cells, lowers blood pressure in hypertensive patients having good organ perfusion particularly with increased renal blood flow. Sustained-release verapamil for once a day dosing is available for the treatment of hypertension. Constipation is a prominent side effect. Headache, dizziness, and edema are frequent and verapamil can sometimes cause AV conduction disturbances and AV block. Verapamil should not be used in combination with -adrenoceptor blockers because of the synergistic negative effects on heart rate and contractile force. 

The anode material in SOF(7s is a cermet (rnetal/cerarnic composite material) of 30 to 40 percent nickel in zirconia, and the cathode is lanthanum rnanganite doped with calcium oxide or strontium oxide. Both of these materials are porous and mixed ionic/electronic conductors. The bipolar separator typically is doped lanthanum chromite, but a metal can be used in cells operating below 1073 K (1472°F). The bipolar plate materials are dense and electronically conductive. 

In addition to intracellular heme-containing proteins, big-conductance calcium-dependent K+ (BKCa) channels and calcium-spark activated transient Kca channels in plasma membrane are also tar geted by CO [3]. As well known, nitric oxide (NO) also activates BKca channels in vascular smooth muscle cells. While both NO and CO open BKCa channels, CO mainly acts on alpha subunit of BKCa channels and NO mainly acts on beta subunit of BKca channels in vascular smooth muscle cells. Rather than a redundant machinery, CO and NO provide a coordinated regulation of BKca channel function by acting on different subunits of the same protein complex. Furthermore, pretreatment of vascular smooth muscle... 

Use of biochemical and biological information for bioprocesses is also significant to the advancement of BRE. Here, the information on the signal transduction from external Ca was utilized for regulation of ginsenoside biosynthetic pathway of cultured cells of P. notoginseng. A quantitative study on the effects of external calcium and calcium sensors was conducted to... 

The mechanism of these effects involves enhanced depolarization of these cells due to decreased potassium permeability and increased sodium and calcium permeability. With fewer K+ ions leaving the cell and with more Na+ and Ca++ ions entering the cell, the inside of the cell becomes less negative and approaches threshold more rapidly. In this way, action potentials are generated faster and travel through the conduction pathway more quickly so that the heart can generate more heartbeats per minute (see Figure 14.1). 

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