Activation Na+channels

Transmitter-gated ion channel Voltage-activated Na+ channel Voltage-activated Ca + channel... 

Na+, are voltage-activated Na+ channels involved Ca2+, are voltage-activated Ca2+ channels involved , increase J., decrease n.d., not determined NA, noradrenaline DA, dopamine VTA, ventral tegmental area. 

A dramatic increase in Na"" permeability requires a dramatic increase in the number of channels that allow Na"" to enter the cell. Thus, the resting p is only a small frac tion of what it could be because most membrane sodium channels are closed at rest. What stimulus causes the hidden Na" channels to reveal themselves It turns out that the activation of these Na channels is triggered by membrane depolarization. When is at its usual resting levels around -70 mV, these Na" channels are closed and p is low. However, depolarization causes the channels to open. Because the voltage-activated Na channels respond to depolarization, the response of the membrane to depolarization is regenerative, and thus explosive (Figure 10.3). A small depolarization of the membrane opens Na" channels, which causes influx of Na"" into the cell and additional depolarization, which in turn opens more Na" channels. This explains the all-or-none nature of the action potential once it is triggered, it runs to completion. 

Source Gleitz e al. (1996a) Kavain inhibits non-stereospecifically veratridine activated Na channels. Vlanta Medica, 62, 580—581, with permission from Georg Thieme Verlag. 

Na ]i and [Ca i and the release of endogenous glutamate from cerebrocortical synaptosomes found that both kavalactones were equally effective, confirming a non-stereospecific inhibition of veratridine-activated Na channels (Gleitz etal., 1996a). 

Also known as atraxin. Toxic component of the funnel web spider Atrax robustus. Disrupts ACh vesicles and depletes the nerve terminals of ACh. MW 15 000-20 000. Activates Na channels. 

Minor sites of action at high concentrations memantine affects many CNS targets, including serotonin and dopamine uptake, nicotinic acetylcholine receptors (nAChRs), serotonin receptors, sigma-1 receptors, and voltage-activated Na+ channels [2,3]. 

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