Physico-chemical studies of taste reception. IV. Response of individual phospholipid membrane to a variety of chemical stimuli.

Variations in the membrane potential across model membranes made of Millipore filter paper and various single phospholipids were measured in response to salt, acid and distilled water. The phospholipids used were phosphatidylcholine (c), spingomyelin (SM), phosphatidylethanolamine (PE), and phosphatidylserine (PS). Results were compared with those obtained with the model membrane made of the total lipids extracted from bovine tongue epithelium, which simulated well the receptor potential observed with intact tast organs. The membrane potential of PE- and PS-membranes increased monotonously with increase of the concentration of 1:1 type salt, while that of PC- and SM-membranes exhibited no appreciable change in 1:1 salt solutions. Application of CaC12 to the membranes brought about a varity of response depending on the species of lipids used. PE- and PS-membranes showed a larger change in the membrane potential than PC- and SM-membranes when pH of the solution was varied. Fe-3+ was strongly absorbed on the surface of PC and SM-membranes, while Fe-3+ bound to PE- and PS-membranes was easily removed by an application of salt solution. A transient increase in the membrane potential was observed when distilled water was applied to the membrane adapted to an appropriate salt solution, which was similar to the water response observed in taste cells. PC- and SM-membranes responded to water when the membrane adapted to either NaC1 or CaC12, but PS-membrane responded only when the membrane was adapted to a solution containing CaC12. PE-membrane did not respond to water in any cases examined. The membrane prepared with a mixture of two species of phospholipids responded neither to salt nor to water, while the membranes prepared with the total lipids or a mixture of three species of lipids in appropriate ratio responded to both. The water response of the total lipids membrane vanished in a high temperature medium, while the water response of PC-membrane retained in all temperature ranges examined, i.e. between 20 degrees and 62 degrees C. The results obtained suggest that a mosaic structure, where each domain has different functions against various chemical stimuli, is formed on the surface of the model membrane made of the total lipids.