Modulation of Acid Sensing in Pulmonary C-Fiber Sensory Nerves by Protease-activated Receptor-2

The long-term goal of this research project is to elucidate the mechanisms of acid sensing in bronchopulmonary C-fibers and its effect on cardiopulmonary functions. Tissue acidosis frequently occurs in various pathophysiological conditions including inflammation, ischemia, and carcinogenesis. Endogenous or exogenous airway acidification can cause cardiorespiratory symptoms that are at least in part mediated through the activation of bronchopulmonary C-fibers and the subsequent reflex responses. However, the acid sensing mechanism in vagal bronchopulmonary sensory nerves is not completely understood, and its regulation under pathophysiological conditions is not known. Protease-activated receptor-2 (PAR2) is expressed in the airways and lungs. The elevated levels of both the endogenous agonists and the expression of PAR2 have been detected under airway inflammatory conditions. In view of the important role of vagal bronchopulmonary C-fiber sensory nerves in regulating cardiopulmonary functions especially under pathophysiological conditions, the main objective of this proposal is to uncover the cellular/molecular mechanism underlying the modulation of acid sensing in vagal pulmonary C-fibers by PAR2 activation that occurs during airway inflammation. Five specific aims are proposed in this project: 1) to determine if activation of PAR2 enhances pulmonary C-fiber-mediated cardiopulmonary responses to acid stimulation in anesthetized rats; 2) to determine if activation of PAR2 enhances the acid-evoked increase of intracellular Ca2+ in isolated vagal pulmonary C-neurons; 3) to identify the expression of ASIC subtypes and TRPVI that responsible for the acid sensing in pulmonary C-fibers by single-cell RT-PCR; 4) to investigate the effect of PAR2 activation on acid-evoked whole-cell responses in isolated pulmonary C-neurons; and 5) to investigate the effect of PAR2 activation on the single-channel activities evoked by acid in isolated pulmonary C-neurons. Single-fiber recording, Ca2+ imaging, single-cell RT-PCR, whole-cell and single-channel patch-clamp recordings will be carried out in anesthetized rats or in isolated neurons. Our preliminary studies have already demonstrated the feasibility of the proposed studies. Results obtained from this project will provide the important information regarding the acid sensing mechanism in vagal pulmonary C-fibers and its modulation by PAR2 in airway inflammatory conditions. ii~ Amount Requested: $77,000 $77,000 $77,000 $77,000 ~ $0