title: Influence of proton availability on intracapillary CO2-HCO3(-)-H+ reactions in isolated rat lungs.
abstract: Transcapillary CO2 exchange entails a transient perfusate CO2-HCO3(-)-H+ disequilibrium, leading to net loading or unloading of blood HCO3-. Perfusate reequilibration may or may not reach completion during the time of capillary transit, depending on the rate of intracapillary CO2-HCO3(-)-H+ reactions. Failure to reestablish equilibrium within the "open" capillary system leads to continued reequilibration in the "closed" postcapillary vasculature with resultant shifts in postcapillary perfusate PCO2, pH, and [HCO3-]. In the present study, we determined the effects of perfusate nonbicarbonate buffer capacity (beta) on intracapillary CO2-HCO3(-)-H+ reactions in isolated saline-perfused rat lungs. Effects of beta on the rate of transcapillary CO2 excretion (VCO2) and the magnitude of the postcapillary perfusate pH disequilibrium were measured as a function of luminal vascular carbonic anhydrase (CA) activity. The data indicate that beta markedly influenced the kinetics and dynamics of intravascular CO2-HCO3(-)-H+ reactions. beta affected VCO2 and the relative enhancement of VCO2 by luminal vascular CA. The data emphasize the inadequacies of using traditional "equilibrium" models of the CO2-HCO3(-)-H+ system to investigate capillary CO2 transport and exchange, even in organs (e.g., lungs) that contain significant luminal vascular CA activity.
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
authors.forename: T A
authors.initials: TA
authors.lastname: Heming
authors.forename: A
authors.initials: A
authors.lastname: Bidani
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002021:Buffers; D002196:Capillaries / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008168:Lung / Q000098:blood supply / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D011522:Protons; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001639:Bicarbonates; D002021:Buffers; D011522:Protons; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases