Mechanosensitive currents in the neurites of cultured mouse sensory neurones

Almost all sensory neurones in the dorsal root ganglia have a mechanosensory function. The transduction of mechanical stimuli in vivo takes place exclusively at the sensory ending. For cutaneous sensory receptors it has so far proved impossible to directly record the mechanically gated receptor potential because of the small size and inaccessibility of the sensory ending. Here we investigate whether mechanosensitive currents are present in the neurites of freshly isolated adult mouse sensory neurones in culture. Almost all sensory neurone neurites possess currents gated by submicrometre displacement stimuli (92%). Three types of mechanically activated conductance were characterized based on different inactivation kinetics. A rapidly adapting conductance was found in larger sensory neurones with narrow action potentials characteristic of mechanoreceptors. Slowly and intermediate adapting conductances were found exclusively in putative nociceptive neurones. Mechanically activated currents with similar kinetics were found also after stimulating the cell soma. However, soma currents were only observed in around 60% of cells tested and the displacement threshold was several times larger than for the neurite (approximately 6 microm). The reversal potential of the rapidly adapting current indicated that this current is largely selective for sodium ions whereas the slowly adapting current is non-selective. It is likely that distinct ion channel entities underlie these two currents. In summary, our data suggest that the high sensitivity and robustness of mechanically gated currents in the sensory neurite make this a useful in vitro model for the mechanosensitive sensory endings in vivo.