Membrane properties of two types of basal cells in Necturus taste buds

Abstract

Necturus taste buds contain two types of basal cells: presumptive stem cells and Merkel-like basal cells. Both types of basal cells are small round cells located at the base of the taste bud, indistinguishable from each other with light microscopy. However, with electron microscopy, autoradiography, or immunocytochemistry, these two types of basal cells can be easily distinguished. We isolated basal cells from taste buds, characterized their voltage-dependent currents using gigaseal whole-cell recordings, and processed the cells for electron microscopy or immunocytochemistry. We were able to distinguish two cell types electrophysiologically and to correlate cell type with membrane properties. Isolated Merkel-like basal cells had several voltage- activated currents: transient, TTX-sensitive, inward Na+ current; sustained, saturating outward K+ current; and slowly inactivating inward Ca2+ current. These currents are similar to those observed in taste receptor cells. In contrast, presumptive stem cells from Necturus taste buds only had outward K+ currents.

Postnatal Development of Membrane Excitability in Taste Cells of the Mouse Vallate Papilla

“…Their specific role in taste bud physiology is unknown. According to work on Necturus taste cells (Bigiani and Roper, 1993;Delay et al, 1994;Mackay-Sim et al, 1996), unexcitable cells endowed with potassium current might represent putative stem basal cells or a transitional state during the continuous turnover of taste sensory cells (see below).…”

“…The life span of taste cells is ϳ10 d in fungiform and vallate papillae of the adult rat (Beidler and Smallman, 1965;Farbman, 1980). Many mature taste cells are electrically excitable and are thought to develop from unexcitable, undifferentiated cells within the taste buds (Delay et al, 1986(Delay et al, , 1994. As a consequence, variations in the membrane properties of taste cells in adult animals are expected to occur.…”

Development of voltage-dependent currents in taste receptor cells

“…A minority of receptor cells are inexcitable (Bigiani and Roper, 1993;McPheeters et al, 1994). There are also two types of basal cells in the mudpuppy taste bud: Merkel-like basal cells and basal stem cells (Bigiani and Roper, 1993;Delay et al, 1993Delay et al, , 1994. Merkellike basal cells contain serotonin and are electrically excitable.…”

“…In contrast, basal stem cells are undifferentiated and represent an actively dividing population. They incorporate I'HIthymidine in their nuclei within 12-24 hours after injection of the radioactive nucleotide (Delay and Roper, 1989;Delay et al, 1994).…”

“…Early studies suggested that the stem cells reside in the epithelium surrounding the taste buds and that their progeny migrate laterally, entering the taste bud to become taste receptor cells (Beidler and Smallman, 1965;Scalzi, 1967;Murray, 1973). However, later studies, employing electron microscopy, demonstrate that there is a population of stem cells residing in the taste buds: the undiff'erentiated basal cells described above (Delay et al, 1986(Delay et al, , 1994Delay and Roper, 1989). Quantitative [3H]thymidine analysis of cell lineage in the mouse vallate taste bud suggests a single lineage of cell types in the taste bud from basal cell to dark receptor cell to light receptor cell (Delay et al, 1986).…”