Mechanisms of CO2 transport in rectal salt gland of Aedes. II. Site of Cl(-)-HCO3(-) exchange.

In the previous paper [Am. J. Physiol. 246 (Regulatory Integrative Comp. Physiol. 15): R727 - R734 , 1984] evidence was presented that indicated HCO3(-) transport in the microperfused rectal salt gland of Aedes dorslis larvae is mediated by a 1:1 exchange of luminal Cl(-) for serosal HCO3(-). The present work demonstrates clearly that the anterior segment is the site of Cl(-)HCO3(-) exchange. Changes in total CO2 concentration of collected perfusates are the same in perfused anterior segments as in whole, perfused salt glands. Furthermore Cl(-) reabsorption in the perfused anterior segment is equivalent to total CO2 secretion and is completely inhibited by bilateral CO2 and HCO3(-) removal. Contrary to a previous hypothesis, both salt gland segments are capable of secreting strongly hyperosmotic fluids containing high concentrations of Na+, Cl(-), and HCO3(-)-CO3(2-).