抄録
Electrophysiological recordings of slowly adapting type I mechanoreceptive (SA I) units innervating the rat hairy skin were performed using an in vitro skin-nerve preparation. The skin was placed with the epidermis-side up in a organ bath. Outskirts of touch dome were incised at a depth of about 200μm so that a test solution blowed upon these incisions percolates through the dome. Caffeine (1-10 mM) blowed from a tube increased the responses of SA I unit to a constant mechanical indentation of 100μm in a dose-dependent manner. Application of 10 mM caffeine increased the response of SA I units by 45-105% (mean=73%, n=9) of the value in the absence of caffeine and shifted stimulus-response relation curves upward without changing the indentation threshold of 12-25μm. 10 mM caffeine did not almost induce spontaneous discharges, unlike the findings in rat sinus hair type I units. On the other hand, solitary Merkel cells freshly dissociated from the rat footpad skin were investigated with whole-cell configurations of the patch clamp technique. At a holding potential of -30mV, extracellular application of caffeine (10mM) produced a TEA-sensitive outward transient current, lasting several seconds, with an increase of conductance in many cells tested. In some Merkel cells, 10 mM caffeine produced an outward transient current followed by an inward sustained current, lasting a minute or longer, with a decrease in membrane conductance. [Jpn J Physiol 54 Suppl:S174 (2004)]
