Evidence for glutamate receptor mediated transmission at mechanoreceptors in the skin

The functional role of Merkel cells in the mechanosensitivity of the slowly adapting type I responses has been a controversial issue for many years. Here we show, for the first time, that glutamate receptor-mediated transmission is largely responsible for the static component of the slowly adapting type I response. An isolated sinus hair preparation was used to study the two types (I and II) of slowly adapting units. A broad spectrum ionotropic glutamate receptor antagonist kynurenate (1-10 mM) caused reliable and dose-dependent reductions in the static component of type I unit responses to mechanical stimulation. In addition, an amino acid transmitter candidate aspartate applied to the preparation selectively increased responses in type I units but not responses in type II units. This evidence establishes that the Merkel cell is a mechano-electric transducer, and challenges prevailing views that the Merkel cell acts merely as a support or target cell in the epidermis.