EFFECT OF AQUEOUS SOLUTIONS OF SOME 1-1 ELECTROLYTES ON ELECTRICAL RESPONSE OF TYPE 1 (SALT) CHEMORECEPTOR CELL IN LABELLA OF PHORMIA

The former classification of the four known chemoreceptor cells in the labellar sensilla trichodea of Phormia regina (salt, sugar, water, and anion receptors) is rejected as too teleological and replaced by types 1, 2, 3, and 4 respectively. The effects of solutions of monovalent ion-pair (1:1) electrolytes on both action potential and receptor potential modulated electrical responses of the type 1 cell are re-examined. Unstimulated response with the sensillum can only be detected in types 1 and 3 cells; in the former the mean frequency of discharge of action potentials (APGF) is 2·5 impulses/sec. The APGF of the type 1 cell is plotted against stimulus activity of KCl, KBr, KI, and NaCl at constant temperature for an instant 0·35 sec after the commencement of stimulation. Mean time-courses of APGF are plotted against elapsed stimulation time for several activities of NaCl and KCl stimulus solutions. A build-up of APGF is always observed in the initial 10 to 30 msec of response before the adapting decline. Relative d.c. displacements representing changes in potential across the receptor membrane are plotted against the activity of stimulus electrolyte for KCl, KBr, and KI. Solutions of choline chloride suppress unstimulated discharge of the type 1 cell at high concentrations (1-3 M), and cause hyperpolarization of the receptor membrane. This may be due to excess chloride ion on the outside of the receptor membrane in the presence of large, non-permeant cations. Abbreviations and symbols: APGF Frequency of generation of action potentials fi, fi Individual and mean APGF at any given instant fs, fs Individual and mean APGF at ts = 0·35 sec representing 'steady state' of response fu, fu Individual and mean APGF when receptor is not stimulated ts Time elapsed since the commencement of stimulation a± Mean electrolytic activity of a given component of the stimulus solution. Other symbols are defined where they appear in the text. © 1968.