Tubocurarine, open channel

Tubocurarine - Open Channel Blocker With Low Unblocking Rate... 

Some antagonists combine the ability to block open ion channels with a competitive action at or near the agonist binding site. A well-characterized example is the nicotinic blocker tubocurarine (see Chapter 6). Agonists may also be open channel blockers, thus limiting the maximal response that they can elicit. Such agents (e g., decamethonium) may therefore behave as partial agonists when tested on an intact tissue ... 

Tubocurarine. Neuronal nicotinic receptors are blocked by micromolar concentrations of (+)-tubocurarine, which is an effective, slow dissociating open channel blocker on ganglionic receptors (280). Nevertheless, there is no evidence that the block involves "trapping" of tubocurarine (291). This compound is likely to have additional effects, other than simple open channel block, given that effects compatible with a partial agonist action... 

A second family of K -channels comprises the Ca -sensitive K -channels - there are three recognized currents of this type. One, the high-conductance Ca -activated K -channel (Ibkicx)) - also called maxi-K channel, or BK channel - is blocked by TEA, Ba, quinine, tubocurarine, charybdotoxin, iberiotoxin, noxiustoxin, soyasaponin and penitrem A. This channel shows voltage-dependence, and the open-state probability of this large conductance channel increases with a rise in [Ca ] over the range O.l-lOpM, and... 

When d-tubocurarine binds at the acetylcholine receptor site, it prevents opening of the ion channels that depolarize the membrane. This prevents a nerve impulse, and results in paralysis. 

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