Date of Award:

12-2010

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Timothy A. Gilbertson

Committee

Timothy A. Gilbertson

Committee

Jon Y. Takemoto

Committee

Gregory J. Podgorski

Committee

Joan M. Hevel

Committee

Silvana Martini

Abstract

A number of studies have demonstrated the ability of free fatty acids to activate taste cells and elicit behavioral responses consistent with there being a taste of fat. Here I show for the first time that long chain unsaturated free fatty acid, linoleic acid, depolarizes taste cells and elicits a robust intracellular calcium rise via the activation of transient receptor potential channel type M5. The linoleic acid-induced responses depend on G protein-phospholipase C pathway indicative of the involvement of G protein-coupled receptors in the transduction of fatty acids. Mice lacking transient receptor potential channel type M5 exhibit no preference for and show reduced sensitivity to linoleic acid. Together, these studies show that transient receptor potential channel type M5 plays an essential role in fatty acid transduction and suggest that fat may reflect a bona fide sixth primary taste. Studies to identify the types of taste cells that respond to fatty acids show that both type II and type III taste cells express fatty acid-activated receptors. Fatty acids elicit robust intracellular calcium rise primarily in type II taste cells and a subset of type III taste cells. However, a significant subset of type II taste cells respond to high potassium chloride, which has been broadly used as the indicator for type III taste cells as well, suggesting the expression of voltage-gated calcium channels in these cells. This finding conflicts with previous studies that type II taste cells lack voltage-gated calcium channels. To explore if voltage-gated calcium channels are expressed in subsets of type II taste cells, transgenic mice with type II or III taste cells marked by green fluorescent proteins are used. Results show that a subset of type II taste cells exhibit voltage-gated calcium currents, verifying the expression of voltage-gated calcium channels in these cells. These results question the utility of being able to use high potassium chloride solution to identify unequivocally type III taste cells within the taste buds. A model for the transduction of fatty acids in taste cells consistent with these findings and our previous data is presented.

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This work made publicly available electronically on December 23, 2010.

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