Ion influx

Sodium channels open more rapidly than K+ channels because they are more voltage sensitive and a small depolarization is sufficient to open them. Larger changes in membrane potential associated with further cell excitation are required to open the less voltage-sensitive K+ channels. Therefore, the increase in the permeability of K+ ions occurs later than that of Na+ ions. This is functionally significant because if both types of ion channels opened concurrently, the change in membrane potential that would occur due to Na+ ion influx would be cancelled out by K+ ion efflux and the action potential could not be generated. 

Ca++ channels start to become activated allowing Ca++ ion influx, which continues to depolarize the membrane toward threshold. 

Fas ligand and interleukin-ip), the neurotransmitter glutamate and thrombin. Like tumor necrosis factor (TNF) receptors, Fas is coupled to downstream death effector proteins that ultimately induce caspase activation (Ch. 22). Fas and TNF receptors recruit proteins called FADD and TRADD respectively FADD and TRADD then activate caspase-8, which, in turn, activates caspase-3 (Fig. 35-4). Calcium ion influx mediates neuronal apoptosis induced by glutamate receptor activation calcium induces mitochondrial membrane permeability transition pore opening, release of cytochrome c and caspase activation. Interestingly, in the absence of neurotrophic factors some neurotrophic factor receptors can activate apoptotic cascades, the low-affinity NGF receptor being one example of such a death receptor mechanism [23],... 

In regards to necrosis, it is clear that the old adage an ounce of prevention is worth a pound of cure applies. Agents that stabilize ion homeostasis have proved to be effective in preventing necrosis in cell culture studies. For example, drugs that activate plasma membrane potassium ion channels or chloride ion channels can prevent membrane depolarization and so inhibit sodium and calcium ion influx. Agents that prevent large sustained increases in intracellular free calcium levels can also prevent neuronal... 

The molecules that transduce noxious heat or cold are members of the transient receptor potential (TRP) receptor family. TRP proteins (Table 57-2) form tetra-meric nonselective cation channels within the plasma membrane, allowing sodium and calcium ion influx [4]. The TRPV3 channel is activated at temperatures between 31 and39°C, TRPV1 at43°C, and TRPV2 at 52-55°C. The heat pain threshold in humans is 43°C, suggesting that... 

Sodium channels are key in conveying nociceptive information from the periphery to the CNS. Voltagegated sodium-ion channels (VGSC) allow Na+ ion influx... 

Theophylline and aminophylline may produce bronchodilation by inhibition of phosphodiesterase (thereby increasing cyclic adenosine monophosphate levels), inhibition of calcium ion influx into smooth muscle, prostaglandin antagonism, stimulation of endogenous catecholamines, adenosine receptor antagonism, and inhibition of release of mediators from mast cells and leukocytes. 

Physiologic effect Inhibition of ion conductance Repetitive firing, shift of voltage dependence of activation Inhibition of phosphorylase phosphatases 1 and 2a Receptor-induced depolarization and excitation Unknown Ciguatoxin repetitive firing, shift of voltage dependence of activation Maitotoxin calcium ion influx... 

A) Antagonism of chloride ion influx at the GABA receptor-chloride channel complex... 

Mechanism of Action An Iminostllbene derivative that decreases sodium and calcium ion influx into neuronal membranes, reducing post-tetanic potentiation at synapses. Therapeutic Effect Reduces seizure activity. 

Diltiazem is a calcium ion influx inhibitor which inhibits the transmembrane influx of calcium ions into cardiac muscle and smooth muscle without changing serum calcium concentration. 

Akerman, K.E., 1978, Changes in membrane potential during calcium ion influx and efflux across the mitochondrial membrane, Biochim. Biophys. Acta 502, pp. 359-366... 

The action potential recorded from a cardiac Purkinje fiber is shown in Figure 23-1. At rest, the interior of the cell is negative relative to the cell s exterior. As in other excitable tissues (neurons, skeletal muscle), an action potential occurs when the cell interior suddenly becomes positive (depolarizes), primarily because of sodium ion influx. The cell interior then returns to a negative potential (repolarizes), primarily because of... 

Krueger BK, Font J, Greengard P (1977) Depolarization-induced phosphorylation of specific proteins, mediated by calcium ion influx, in rat brain synaptosomes. J Biol Chem 252 2764-73 Kubista H, Boehm S (2006) Molecular mechanisms underlying the modulation of exocytotic noradrenaline release via presynaptic receptors. Pharmacol Ther 112 213 12 Kulik A, Vida I, Fukazawa Y et al (2006) Compartment-dependent colocalization of Kir3.2-containing K+ channels and GABAB receptors in hippocampal pyramidal cells. J Neurosci 26 4289-97... 

Fig. 3.18 (A) Schematic drawing of a phospholipid bilayer containing a membrane-solvated globular protein that has a sodium channel in the closed configuration. (B) The globular protein has expanded in conformation to allow a sodium ion influx. (C) Anesthetic molecules have fluidized the entire bilayer and destroyed the regions of solid phase.

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