Mathematical Model of ATP Secretion in Taste Cells of the Type II
The taste bud, a functional unit of the peripheral mammalian taste system, consists of 50–80 densely packed cells of several types, including taste cells of the type I-III. Apart from identifying tastant molecules, taste cells encode sensory information in the form of stimulus-dependent release of an afferent neurotransmitter stimulating the taste nerve. The afferent neurotransmission in type II cells is rather peculiar compared to exteroreceptors operating in other sensory organs of vertebrates. In particular, taste cells of the type II employ ATP as an afferent neurotransmitter and release it via ATP- permeable ion channels. Although taste cells are axonless, type II cells are electrically excitable, and neurotransmitter secretion is controlled by action potentials. Here we elaborated a mathematical model of ATP release with a voltage-gated ATP-permeable channel as a conduit of ATP efflux. Based on this model, we analyzed a voltage dependence of steady-state ATP release as well as transient ATP secretion stimulated by a voltage pulse. These computer simulations revealed certain features of channel-mediated ATP secretion that led us to the following inference. Compared to ATP release mediated by gradual receptor potential, the electrical excitability of type II cells provides the higher reliability of synaptic transmission, renders it quantal, and widens a dynamic range of detectable taste stimuli.