Central chemoreception is the mechanism by which specialized CO2/pH sensors (i.e., chemoreceptors) located in the brainstem regulates breathing in response to changes in tissue pH. This mechanism is important for normal breathing, especially during sleep, and disruption of chemoreception is thought to contribute to several pathological states including central sleep apnea, periodic breathing and central hypoventilation syndrome. Despite intensive investigation, cellular and molecular mechanisms underlying central chemoreception remain poorly understood. Recent evidence indicates that pH-sensitive neurons located in the retrotrapezoid nucleus (RTN) are important chemoreceptors. Evidence also indicates that CO2/H+-evoked ATP release in the RTN contributes to integrated output of the RTN and respiratory drive. We hypothesize that pH-sensitive RTN glial cells are the source of this purinergic drive to breathe. We propose that a discreet population of RTN glia sense H+ by inhibition of heteromeric Kir4.1-Kir5.1 channels, and release ATP to activate pH-sensitive neurons by activation of P2 receptors. We also propose that a portion of H+-evoked ATP released in the RTN will be hydrolyzed to adenosine and serve to limit chemoreceptor activity by initiating vasodilation to buffer tissue pH. The proposed research will use a combination of electrophysiological, immunohistochemical and genetic approaches to determine the cellular identity of pH-sensitive RTN glia, the molecular mechanism by which they sense pH, and their interactions with pH-sensitive neurons and local vasculature. The four specific aims of this project are: 1) determine the cellular identity of pH-sensitive RTN glia, 2) determine the molecular mechanism by which RTN glia sense changes in pH, 3) identify interactions between pH-sensitive glia and pH-sensitive neurons, 4) determine if pH-sensitive glia in the RTN modulate local microcirculation. It is our hope that determining these mechanisms will lead to new therapeutic avenues for the management of conditions resulting from suppressed respiratory drive.
The results of these studies will identity two novel mechanisms by which glial cells contribute to the mechanism by of chemoreception. Specifically, we will establish that a population of glial cells sense H+ by inhibition of Kir4.1-Kir5.1 channels and can provide an excitatory purinergic drive to the neural network that controls depth and frequency of breathing. We also determine that these pH-sensitive glia regulate vascular tone to help buffer tissue pH and limit chemoreceptor activity. Determining these basic cellular mechanisms will help guide new pharmacological approaches for the treatment of respiratory control disorders.
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