The cellular factors that determine the magnitude of the firing rate response of chemosensitive neurons to increased CO 2 /H + are typically attributed to acid‐induced increased firing rate pathways (accelerators). However, a marked reduction in the CO 2 /H + ‐induced increased firing rate during postnatal development has been observed in neurons from the locus coeruleus (LC). This response has been hypothesized to be due to the development of a decelerating pathway that arises from CO 2 /H + activation of Ca 2+ channels, which in turn induces the Ca 2+ ‐activation of K Ca channels. In order to investigate the contribution of such a braking pathway in the magnitude of the firing rate in individual neurons, we have developed a preliminary computational model of excitable single neuron that simulates the voltage‐gated currents as well as the pH and Ca 2+ sensitive K + currents using the Hodgkin‐Huxley formulation. In our simulations we found that inhibition of the L‐type Ca 2+ current led to a larger hypercapnic‐induced firing rate response. These findings constitutes theoretical evidence that the cellular factors limiting the firing rate response of chemosensitive neurons are associated with acid activated Ca 2+ and Ca 2+ activated K Ca currents, allowing us to conclude that a braking pathway may play a more significant role in setting neuronal chemosensitivity. Supported by NIH Grant HL56683.