Effects of changed lipid composition on responses of liposomes to various odorants: possible mechanism of odor discrimination

In a previous paper [Nomura, T., & Kurihara, K. (1987) Biochemistry (preceding paper in this issue)], we showed that azolectin liposomes are depolarized by various odorants and there is a good correlation between the responses in the liposomes and the frog or porcine olfactory responses. In this study, we examined effects of changed lipid composition on responses of liposomes to various odorants. The membrane potential changes in response to odorants were monitored with the fluorescent dye 3,3'-dipropylthiocarbocyanine iodide [diS-C3(5)]. Egg phosphatidylcholine (PC) liposomes showed depolarizing responses to nine odorants among ten odorants tested. The magnitudes of depolarization by alcohols were similar to those in azolectin liposomes, but those by other odorants were much less than those in azolectin liposomes. Addition of sphingomyelin (SM) to PC led to an increase in the magnitude of depolarization by most odorants. Addition of phosphatidylethanolamine (PE) to PC (PE/PC = 0.25) led to depolarizing responses to four odorants among six odorants tested, and a further increase in PE content (PE/PC = 0.54) led to depolarizing responses only to two odorants. Addition of SM to the lipids of this composition of PC and PE [SM/(PC + PE) = 0.22] led to depolarizing responses to four odorants again. Liposomes made of a mixture of SM, PE, and PC exhibited depolarizing responses to four odorants tested, and addition of cholesterol to the lipids [cholesterol/(PC + PE + SM) = 0.05 and 0.11] led to depolarizing responses only to two and one odorant, respectively. Thus, changes in lipid composition of liposomes led to great changes in specificity of the responses to odorants.(ABSTRACT TRUNCATED AT 250 WORDS)