Membrane properties and cell ultrastructure of taste receptor cells in Necturus lingual slices

1. Whole cell patch-clamp recordings and electron micrographs were obtained from cells in Necturus taste buds in lingual slices to study their membrane properties and to correlate these properties with cell ultrastructure. 2. Two different populations of taste receptor cells could be identified: one type possessed voltage-gated Na+ and K+ (noninactivating) currents (group 1 cells); the other type possessed only K+ (inactivating) currents (group 2 cells). 3. The zero-current (''resting'') potential (V-0) and whole cell resistance (R(0)) of these two types of taste cells differed significantly. For group 1 cells, on average, V-0 = -75 mV and R(0) = 24.6 G Omega, and for group 2 cells, V-0 = -49 mV and R(0) = 48.9 G Omega. The difference in R(0) was not explained completely by differences in cell sizes, suggesting that intrinsic membrane properties differed between the taste cell populations. 4. Cells injected with biocytin were inspected with the electron microscope after tissues were reacted with diaminobenzidine. The majority (14 of 16) of cells with voltage-gated Na+ and K+ currents (group 1 cells) were characterized by abundant rough endoplasmic reticulum and dense granular packets in the apical process. These are features of dark cells. All the cells that only possessed K+ currents (group 2 cells) were characterized by well-developed smooth endoplasmic reticulum and an absence of granular packets. These features characterize Light cells. 5. These findings indicate that there is a good, although not exact, correlation between electrophysiological properties and cell morphotype in Necturus taste bud cells. All dark cells possessed Na+ and K+ currents and thus would be expected to be capable of generating action potentials. Most light cells only possessed outward K+ currents and thus would be incapable of generating action potentials.