Channel opening, mechanism

Vasodilators are a group of dtugs, which relax the smooth muscle cells of the blood vessels and lead to an increased local tissue blood flow, a reduced arterial pressure and a reduced central venous pressure. Vasodilators reduce the cardiac pre-load as well as after-load and thereby reduce cardiac work. They are used in a variety of conditions including hypertension, cardiac failure and treatment/prevention of angina pectoris. Major groups are Ca2+-channel blockers (e.g. dihydropyridines), NO-donators (e.g. organic nitrates), K+-channel openers (minoxidil), phosphodiesterase inhibitors (e.g. sildenafil), Rho-kinase inhibitors (e.g. Y27632) or substances with unknown mechanism of action (e.g. hydralazine). Inhibitors of the... 

Another mechanism postulated to explain the conductometric behavior of these microemulsions attributes it to the transfer of sodium counterions from a reversed micelle to another through water channels opened by intermicellar coalescence [255-258],... 

The first physically plausible mechanism for receptor activation was proposed by del Castillo and Katz (1957). They made the important distinction that agonist binding and channel opening of the AChR must occur as two separate steps ... 

Expressions relating the equilibrium occupancy of any state in this mechanism to agonist concentration can be derived as described in Chapter 1. If we define the equilibrium constants for agonist binding as K = kffk+1 and K2 = k 2lk+2 and a constant E describing the efficiency of channel opening (equivalent to efficacy) as E= (l a, then the equilibrium occupancy of the open state (A2R ) will be ... 

With mechanisms such as these, it is often possible to simplify the analysis of the action of a channel blocker by assuming that agonist binding is much faster than channel opening and closing and then combining several closed states together so that the mechanism approximates a three-state system ... 

This is an important result. The simple open-channel block mechanism predicts that the total open time per burst is the same as the mean open time in the absence of blocker (Neher, 1983), even though openings are now chopped up by channel blockages. In fact, for channels that give bursts of openings in control recordings, the total open time per burst is constant in the presence or absence ... 

During excitation, ion channels open and close and a few ions flow 98 Gating mechanisms for Na+ and K+ channels in the axolemma are voltage-dependent 98... 

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