Response ofNitella internodal cell to chemical stimulation

Abstract

Electrical response of excitable internodal cell ofNitella was studied by applying various kinds of odorants to the cell. Changes in membrane potential and resistance during responses induced by odorants were measured intracellularly under a variety of ionic environments in the media. Results were: 1) Some odorants (coumarin, isoamylacetate, methylacetate, 1-octanol, 1-butanol, 1-propanol) produced an all-or-nothing type action potential when the concentration of odorant exceeded a certain threshold. The action depended on the odorant concentration,C. Other odorants (heptanoic acid, β-ionon) induced gradual depolarization of the membrane potential without evoking an action potential. 2) Membrane resistanceR _m changed in various ways during depolarization: some odorants led to a temporal or gradual decrease inR _m, and others caused an increase inR _m when the membrane potential was depolarized by the application of odorants. 3) Magnitude of response to odorantsOR was found to be represented by the following equation: $$OR = (\alpha + \beta \sqrt 1 )\log (C/C_{th} ) for C \geqq C_{th} $$ where α and β are constants for a given odorant,I the ionic strength in the medium, andC _th the threshold concentration of the odorant. 4) Plots of olfactory threshold of human and of internodal cell ofNitella gave a straight line having slope unity. 5) Local application of odorants on the internodal cell induced impulses which transmitted from the part treated by odorants to the other portion. Physico-chemical and physiological implications of the results obtained were discussed.