Abstract
Frog taste discs contain three types of cells (type Ib, type II and type III cells). These three types of cells have voltage-gated Na+ inward currents. Merkel-like basal cells of the taste disc contain serotonin (5-hydroxytryptamin, 5-HT). Therefore, 5-HT has been thought to play an important role in gustatory transduction. In the present study, the effects of 5-HT on membrane properties of three types of cells of the bullfrog (Rana catesbeiana) taste disc were investigated. The patch clamp technique was used to make recordings from taste cells in vertical slices of taste discs. Cell types were identified by staining with Luciffer yellow in a pipette. The amplitudes of peak INa in type Ib, II and III cells obtained in the present study were –2153.1 ± 227.7 pA (mean ± SD, n = 5), –1423.1 ± 155.5 pA (n = 13) and –754.1 ± 59.0 pA (n = 6), respectively. External application of a 5-HT1A receptor agonist, (+/-)-8-OH-2-(D1-n-propyl-amino)tetralin (8-OH DPAT) (20 μM), inhibited 14-22% of the peak INa in three types of cells, and the effect of 8-OH DPAT was reversible. These inhibitory effects were statistically significant (P < 0.05). The present findings indicate that the effects of 5-HT on the three types of cells were similar, suggesting that the release of 5-HT from Merkel-like basal cells affects electrical membrane properties of adjacent cells rather than a specific type of cell. [Jpn J Physiol 55 Suppl:S159 (2005)]
