The Influence of Carbon Dioxide on Cellular Cyclic Adenosine Monophosphate

Abstract

Inorganic carbon is fundamental to the physiology of all organisms, however elevated CO2 is generally detrimental. Numerous class III adenylyl cyclases (AC) from both prokaryotic and mammalian organisms have been shown to respond to inorganic carbon in vitro, however, at present there is limited evidence in vivo. This thesis demonstrates in cellulo evidence that hypercapnia CO2 blunts agonist induced cAMP signalling. The eect of CO2 is independent of changes in intracellular and extracellular pH, independent of the mechanism used to activate the cAMP signalling pathway, and is independent of the cell line employed. Through a combination of pharmacological and genetic tools this eect of elevated CO2 on cAMP signalling is demonstrated to require Ca2+ ion release from IP3 receptors in the endoplasmic reticulum. Consistent with these ndings, CO2 caused an increase in cytoplasmic Ca2+ concentrations which require the presence of active IP3 receptors and is absent under comparable acidotic conditions. Physiological relevance for this signalling mechanism is demonstrated through activity of the sodium dependant proton exchanger NHE3. This transporter exhibits well-characterised inhibition by cAMP dependant protein kinase PKA to increase bicarbonaturia in vivo. Overall these results provide conclusive evidence of potentially profound eects of inorganic carbon on intracellular cell signalling, which could lead to signicant insight into the pathophysiology and treatment of numerous disorders including metabolic acidosis, reperfusion injuries, acute lung injury and obesity