The conversion of plasma HCO 3 ? to CO2 by rainbow trout red blood cells in vitro: adrenergic inhibition and the influence of oxygenation status

Abstract

This study employed a recently developed radioisotopic assay (Wood and Perry 1991) to examine the inhibition, induced by catecholamines, of the conversion of plasma HCO 3 (-) to CO2 in acidotic trout blood, and the influence of oxygenation status on the response. Blood was incubated in vitro at PCO 2= 2 torr, and 10(-6) M noradrenaline was employed as the adrenergic stimulus. In particular we investigated whether the inhibition of plasma HCO 3 (-) conversion could be explained by a limited supply of H(+)s for the intracellular HCO 3 (-) dehydration reaction because of competition by the adrenergically activated Na /H(+) exchanger. Hypoxia (PO 2= 15 torr) was employed as a tool to intensify this competition. Hypoxia raised RBC pHi, pHe, and plasma total CO2 concentration (CCO 2) by the Haldane effect, and increased the magnitude of Na(+)/H(+) activation, expressed as the change in the transmembrane pH gradient (pHe-pHi). However hypoxia did not alter the inhibition of the conversion of plasma HCO 3 (-) to CO2 caused by noradrenaline. Hypoxia itself stimulated the RBC-mediated conversion of plasma HCO 3 (-) to CO2 by about 20% in the presence or absence of noradrenaline. The conversion rate was strongly correlated with pHe, pHe-pHi, and plasma CCO 2 in these experiments, but not with pHi. We conclude that adrenergically mediated inhibition in the conversion of plasma HCO 3 (-) to CO2 by trout RBCs is not due to competitive limitation on intracellular H(+)s, but rather to changes in the electrochemical gradient for HCO 3 (-) entry and/or to CO2 recycling from plasma to RBC. The deoxygenated condition helps to promote CO2 excretion at the level of the RBC.

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

“…1991Perry etal. , 1995Perry and Gilmour 1993;Wood 1994;Wood and Simmons 1994;. For example, Wood (1.994) used this assay to demonstrate that a relative inhibition of HCO 3-dehydration through the rbc occurs following exercise, despite an increase of 50% in the absolute rate.…”

“…For example, Wood (1.994) used this assay to demonstrate that a relative inhibition of HCO 3-dehydration through the rbc occurs following exercise, despite an increase of 50% in the absolute rate. Similarly, the assay was employed by Wood and Simmons (1994) to document the effects of oxygenation status and catecholamines on rbc HCO 3-dehydration. Although the different time courses of HCO 3-dehydration in vivo (1 sec) and in vitro (3 min) make it difficult to predict absolute in vivo CO 2 excretion rates using the in vitro assay (see also the discussion of Wood and Perry 1991), this difficulty is eliminated when the assay is utilized for the detection of relative differences.…”

Functional morphology of nucleated erythrocytes during hypoxia (in vitro experiments)

“…У більшості робіт констатується факт зростання клітинного об'єму [10,17,28]. Процес контролюється катехоламінами (переважно норадреналіном) [20,25], що взаємодіють з поверхневими β-адренорецепторами еритроцитів [15,22] і активують Na + -H + і HCO 3 --Cl --антипорти клітин [17,29]. Дія катехоламінів опосередковується через циклічний аденозинмонофосфат [11].…”