Transduction dynamics of intrapulmonary CO2 receptors

We have developed a functional model for quantitatively characterizing the transduction dynamics of the intrapulmonary CO2 receptors (IPC) in the snake lung. The model was based on experiments in which the neural discharges of several IPCs were recorded in response to abrupt step changes in CO2 concentration. Initial attempts to model the transduction dynamics linearly proved inadequate, although the linear model captured gross features such as rate sensitivity and the existence of two time constants in the adaptation time-course. However, with the incorporation of two static nonlinear features, namely, thresholding and preferential directionality of the rate-sensitive component, it was possible to account for over 80% of the total variation in the data. The model produced accurate predictions of IPC responses to other inputs, such as pseudorandom binary changes in CO2. The model also allows the prediction of IPC discharge in spontaneous breathing given measurements of lung CO2 concentration, and may serve as a starting point for further studies of transduction mechanisms at the cellular level.