Summary
Active HCO t-3 secretion in the anterior rectal salt gland of the mosquito larva,Aedes dorsalis, is mediated by a 1∶1 Cl−/HCO −3 exchanger. The cellular mechanisms of HCO −3 and Cl− transport are examined using ion- and voltage-sensitive microelectrodes in conjunction with a microperfused preparation which allowed rapid saline changes. Addition of DIDS or acetazolamide to, or removal of CO2 and HCO −3 from, the serosal bath caused large (20 to 50 mV) hyperpolarizations of apical membrane potential (V a) and had little effect on basolateral potential (V bl). Changes in luminal Cl− concentration alteredV a in a repid, linear manner with a slope of 42.2 mV/decaloga lCl −. Intracellular Cl− activity was 23.5mm and was approximately 10mm lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl− concentration had no effect onV bl, indicating an electrically silent basolateral Cl− exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated\(a_{HCO_3 }^c \) was 14.4mm. These results show that under control conditions HCO3 enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. A tentative cellular model is proposed in which Cl enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl−-selective channel, and HCO −3 exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl− exit and HCO3 entry, and the effects of serosal addition of the Cl−/HCO3 exchange inhibitor, DIDS, on\(J_{net}^{CO_2 } \) and transepithelial potential (V ic) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl− and HCO −3 movements.
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Strange, K., Phillips, J.E. Cellular mechanism of HCO −3 and Cl− transport in insect salt gland. J. Membrain Biol. 83, 25–37 (1985). https://doi.org/10.1007/BF01868735
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DOI: https://doi.org/10.1007/BF01868735