Abstract
Taste bud cells (TBCs) fire action potentials in response to taste stimuli. Recent studies showed that the action potentials opened hemichannels to release ATP, a neurotransmitter. Voltage-gated Na+ channels consist of α and β subunits. Ten genes encoding α subunits and four genes encoding β subunits have been identified. We investigated the expression of mRNA encoding α and β subunits and electrophysiological properties of voltage-gated Na+ currents in mouse fungiform TBCs. RT-PCR studies using mRNA extracted from taste buds suggested the expression of Nav 1.3, Nav 1.5, and Nav 1.6 α subunits and β1 subunit. In whole-cell clamp experiments, the midpoint of activation and inactivation was ∼-25 mV and ∼-65 mV, respectively. The recovery from inactivation was well fitted with double exponential with tau1 of ∼20 ms and tau2 of ∼800 ms. A subset of TBCs exhibited the Na+ currents in the presence of 1 μ M TTX. The TTX-resistant component was ∼6% of total voltage-gated Na+ currents recorded on membrane depolarization from -70 mV to -20mV. These results suggest that TBCs can be classified into at least two groups based on TTX-sensitivity. One group of TBCs expresses only TTX-sensitive Na+ channels (Nav 1.3 and/or Nav 1.6). Another has a little amount of TTX-resistant Nav 1.5 channels in addition to TTX-sensitive ones. Supported by a COE program (center #J19) granted to Kyushu Institute of Technology by MEXT of Japan. [J Physiol Sci. 2008;58 Suppl:S168]
