Mixture interactions of glutamate and betaine in single squid olfactory neurons

We used nystatin-patch techniques to characterize the responses of squid olfactory receptor neurons to the attractive odorant, L-glutamate, and to study mixture interactions between glutamate and the aversive odorant, betaine. We report that glutamate activates a cation-selective conductance that is permeable to Ca2+, K+, and Na+ and which would depolarize squid olfactory receptor neurons under physiological conditions. The responses to glutamate were concentration dependent. The EC50 of individual cells ranged from 0.3 mmol x l(-l) to 85.0 mmol x l(-l). We found that individual cells were capable of responding to both glutamate and betaine, and that the relative magnitudes of these responses varied from cell to cell. Finally, we report that current responses to binary mixtures of glutamate and betaine are suppressed relative to the sum of the responses to the individual odors in single squid olfactory receptor neurons.