Adenylyl cyclase expression and modulation of cAMP in rat taste cells.
Abaffy, Tatjana, Kristina R. Trubey, and Nirupa Chaudhari.
Department of Physiology and Biophysics, University of Miami School of Medicine,
Miami, Florida 33101
APStracts 10:0060C, 2003.
cAMP is a second messenger implicated in sensory transduction for taste. The identity of
adenylyl cyclase (AC) in taste cells has not been explored. We have employed RT-PCR
to identify the AC isoforms present in taste cells and found that AC 4, 6, and 8 are
expressed as mRNAs in taste tissue. These proteins are also expressed in a subset of taste
cells as revealed by immunohistochemistry. Alterations of cAMP concentrations are
associated with transduction of taste stimuli of several classes. The involvement of
particular ACs in this modulation has not been investigated. We demonstrate that
glutamate, which is a potent stimulus eliciting a taste quality termed umami, causes a
decrease in cAMP in forskolin-treated taste cells. The potentiation of this response by
inosine monophosphate, the lack of response to d-glutamate, and the lack of response to
umami stimuli in nonsensory lingual epithelium all suggest that the cAMP modulation
represents umami taste transduction. Because cAMP downregulation via ACs can be
mediated through Gai proteins, we examined the colocalization of the detected ACs with
Gai proteins and found that 66% of AC8 immunopositive taste cells are also positive for
gustducin, a taste-specific Gai protein. Whether AC8 is directly involved in signal
transduction of umami taste remains to be established.
Received 27 November 2002; accepted in final form 11 February 2003
APS Manuscript Number C556-2.
Article publication pending Am J Physiol Cell Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 25 March 2003