The pharmacology of mechanogated membrane ion channels

In this article, the actions, mechanisms and applications of various ions and drugs that interact with MG channels have been discussed. At present, no compound has been found that displays the high specificity and affinity exhibited by tetrodotoxin or alpha-bungarotoxin that proved so useful in the functional and structural characterization of the voltage-gated Na+ channel and the acetylcholine receptor channel, respectively. Nevertheless, three different classes of compounds have been discovered since Paintal's review that clearly block MG channels. These compounds, represented by amiloride, gentamicin and gadolinium, act mainly on the SA cation channel, which appears to be shared by many nonsensory and some mechanosensory cells. Each class of compound can be distinguished by the voltage and concentration dependence of the block and most likely involves different mechanisms of blocking action. In general, the MG channel blocker pharmacology indicates a variety of "receptor sites" on MG channels. The recognition and acceptance of such receptors should provide added impetus for continued screening for more potent drugs, venoms and toxins. In the case of activators, little is understood of the mechanisms by which the various amphipathic and amphiphilic compounds stimulate MG channels, although different bilayer and protein mechanisms have been evoked. Even less is understood of the role the new class of MG K+ channel and their modulation by fatty acids plays in physiological and perhaps pathological processes. However, given that K+ channels in general tend to reduce the excitability of nerve and muscle, plausible roles include fatty acid regulation of vascular tone and control of neuronal network excitability. In both cases, more detailed understanding is required regarding the physiological stimuli that modulate these channels through their fatty acid receptors. It may turn out that recognition and/or development of cell-type specific agents that activate such MG channels will possess high therapeutic potential. In any case, the observation that MG channels can be chemically blocked and/or activated by a wide range of compounds requires revision of the long-standing conclusion of Paintal that mechanotransduction is a process that has a low susceptibility to chemical influence.