Mechanisms of CO2 transport in rectal salt gland of aedes. I. Ionic requirements of CO2 secretion.

Rectal salt glands of Aedes dorsalis can be successfully isolated and microperfused in vitro. Microperfused salt glands maintain a large, stable transepithelial potential (-40 to -50 mV, lumen negative) and secrete total CO2 at high and stable rates [CO2 net flux ( JCO2net ) = 799 +/- 57 pmol . min-1 . mm-1]. Bilateral Na+ and K+ or serosal Cl- substitutions and serosal addition of 1.0 mM ouabain, 2.0 mM amiloride, or 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid had no effect on JCO2net . Removal of luminal Cl- inhibited JCO2net by 80%, whereas serosal addition of 1.0 mM acetazolamide or 0.5 mM 4,4'-diisothiocyano-2,2'-disulfonic acid inhibited JCO2net by 80 and 40%, respectively. Net Cl- reabsorption ( JClnet = -888 +/- 57 pmol . min-1 . mm-1) was equivalent to total CO2 secretion, suggesting that CO2 transport was mediated by a 1:1 exchange of luminal Cl- for serosal HCO-3.