44 - Mechanosensitive Ion Channels in Eukaryotic Cells

Abstract

This chapter discusses mechanosensitive (MS) ion channels in eukaryotic cells. MS channels are ubiquitous, abundant, and diverse. The chapter also refers briefly to the genetic and molecular work. It is mentioned that MS channel breakthroughs have occurred on three fronts over the last half decade—electrophysiologic, genetic, and molecular. The chapter includes list of the criteria MS channel performing a mechanical cellular task by Morris (1992). The criteria that need to be met can be compared to those that have been met by ligand-gated and voltage-gated channels with established physiological roles. The discussion of explorations of MS channels includes fungal germling of bean rust, Xenopus oocytes MS channels, NMDA (glutamate) channels in mouse neurons, and others. For single-channel recordings, the name "MS channel" carries an implicit assumption that some susceptible gating structure experiences tension in the plane of the membrane and that this biases the channel's open probability. The available information on possible mechanisms of ion channel mechanosensitivity suggests that both the extremes are important. At one extreme, the specialized receptors, cytoarchitecture is central to function. At the other extreme are bacterial MS channels, which can be reconstituted into artificial bilayers and retain their mechanosensitivity. The term MS channel may be reserved for physiological mechanotransducer channels. Although MS channels detectable at the single-channel level have been on the scene for almost two decades, they should only be afforded a status coequal with voltage-gated and ligand-gated channels once it is abundantly clear that their MS gating has a biological meaning. The chapter concludes by stating that the inherent mechanosusceptibility of many other channels also acquires biological meaning (rather than solely biophysical meaning), if it is shown that evolution has had to look for ways to protect cells from unwanted mechanically driven membrane currents.