DEVELOPMENT OF VOLTAGE-DEPENDENT CURRENTS IN TASTE RECEPTOR-CELLS

Taste buds, the specialized end organs of gustation, comprise a renewi ng sensory epithelium. Undifferentiated basal cells become taste recep tor cells by elongating and extending processes apically toward the ta ste pore. Mature taste cells are electrically excitable and express vo ltage-dependent Na+ Ca2+, and K+ currents, whereas basal stem cells ex hibit only slowly activating K+ currents. The question we have address ed in the present study is whether contact with the taste pore is requ ired for expression of voltage-dependent inward currents in Necturus t aste cells. Mature taste cells were distinguished from developing cell s by labeling the apical surface of the cells with fluorescein-isothio cyanate-conjugated wheat germ agglutinin (FITC-WGA), while the tissue was still intact. Elongate cells lacking FITC-WGA staining were interp reted as developing taste cells that had not yet reached the taste por e. Giga-seal whole-cell recording revealed that most developing taste cells lacked inward currents. Although some developing cells expressed inward currents, they were much smaller than those of mature cells, a nd the activation kinetics of the K+ currents were slower than in matu re cells. Electron microscopy confirmed the identity of labeled and un labeled cells. All FITC-WGA-labeled cells exhibited the ultrastructura l characteristics of mature taste receptor cells, whereas most unlabel ed taste cells had a characteristic morphology that was markedly diffe rent from mature taste receptor cells or basal stem cells. These data suggest that contact with the taste pore is required for the developme nt of inward currents in taste cells. (C) 1996 Wiley-Liss, Inc.