Interaction between the second messengers cAMP and Ca2+ in mouse presynaptic taste cells

J Physiol. 2009 Apr 15;587(Pt 8):1657-68. doi: 10.1113/jphysiol.2009.170555. Epub 2009 Feb 16.


The second messenger, 3',5'-cyclic adenosine monophosphate (cAMP), is known to be modulated in taste buds following exposure to gustatory and other stimuli. Which taste cell type(s) (Type I/glial-like cells, Type II/receptor cells, or Type III/presynaptic cells) undergo taste-evoked changes of cAMP and what the functional consequences of such changes are remain unknown. Using Fura-2 imaging of isolated mouse vallate taste cells, we explored how elevating cAMP alters Ca(2+) levels in identified taste cells. Stimulating taste buds with forskolin (Fsk; 1 microm) + isobutylmethylxanthine (IBMX; 100 microm), which elevates cellular cAMP, triggered Ca(2+) transients in 38% of presynaptic cells (n = 128). We used transgenic GAD-GFP mice to show that cAMP-triggered Ca(2+) responses occur only in the subset of presynaptic cells that lack glutamic acid decarboxylase 67 (GAD). We never observed cAMP-stimulated responses in receptor cells, glial-like cells or GAD-expressing presynaptic cells. The response to cAMP was blocked by the protein kinase A inhibitor H89 and by removing extracellular Ca(2+). Thus, the response to elevated cAMP is a PKA-dependent influx of Ca(2+). This Ca(2+) influx was blocked by nifedipine (an inhibitor of L-type voltage-gated Ca(2+) channels) but was unperturbed by omega-agatoxin IVA and omega-conotoxin GVIA (P/Q-type and N-type channel inhibitors, respectively). Single-cell RT-PCR on functionally identified presynaptic cells from GAD-GFP mice confirmed the pharmacological analyses: Ca(v)1.2 (an L-type subunit) is expressed in cells that display cAMP-triggered Ca(2+) influx, while Ca(v)2.1 (a P/Q subunit) is expressed in all presynaptic cells, and underlies depolarization-triggered Ca(2+) influx. Collectively, these data demonstrate cross-talk between cAMP and Ca(2+) signalling in a subclass of taste cells that form synapses with gustatory fibres and may integrate tastant-evoked signals.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • 1-Methyl-3-isobutylxanthine / pharmacology
  • Animals
  • Calcium / metabolism
  • Calcium / physiology*
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels, L-Type / drug effects
  • Calcium Channels, L-Type / physiology
  • Calcium Channels, P-Type / drug effects
  • Calcium Channels, P-Type / physiology
  • Calcium Channels, Q-Type / drug effects
  • Calcium Channels, Q-Type / physiology
  • Calcium Signaling / drug effects
  • Calcium Signaling / genetics
  • Calcium Signaling / physiology
  • Colforsin / pharmacology
  • Cyclic AMP / physiology*
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Glutamate Decarboxylase / biosynthesis
  • Glutamate Decarboxylase / genetics
  • Image Processing, Computer-Assisted
  • Mice
  • Mice, Inbred C57BL
  • Phosphodiesterase Inhibitors / pharmacology
  • Receptors, G-Protein-Coupled / physiology
  • Receptors, Presynaptic / drug effects
  • Receptors, Presynaptic / genetics
  • Receptors, Presynaptic / physiology*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Second Messenger Systems / drug effects
  • Second Messenger Systems / genetics
  • Second Messenger Systems / physiology*
  • Taste Buds / drug effects
  • Taste Buds / physiology*


  • Calcium Channel Blockers
  • Calcium Channels, L-Type
  • Calcium Channels, P-Type
  • Calcium Channels, Q-Type
  • Phosphodiesterase Inhibitors
  • Receptors, G-Protein-Coupled
  • Receptors, Presynaptic
  • Colforsin
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • Glutamate Decarboxylase
  • Calcium
  • 1-Methyl-3-isobutylxanthine