Cellular mechanism of HCO-3 and Cl- transport in insect salt gland

J Membr Biol. 1985;83(1-2):25-37. doi: 10.1007/BF01868735.

Abstract

Active HCO-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 (Va) and had little effect on basolateral potential (Vbl). Changes in luminal Cl- concentration altered Va in a rapid, linear manner with a slope of 42.2 mV/decalog a1Cl-. Intracellular Cl- activity was 23.5 mM and was approximately 10 mM lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl- concentration had no effect on Vbl, indicating an electrically silent basolateral Cl- exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated acHCO-3 was 14.4 mM. These results show that under control conditions HCO-3 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 HCO-3 entry, and the effects of serosal addition of the Cl-/HCO-3 exchange inhibitor, DIDS, on JCO2net and transepithelial potential (Vte) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl- and HCO-3 movements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aedes / metabolism*
  • Animals
  • Bicarbonates / metabolism*
  • Biological Transport
  • Chlorides / metabolism*
  • Epithelium / metabolism
  • Epithelium / physiology
  • Kinetics
  • Larva / metabolism
  • Membrane Potentials
  • Microelectrodes
  • Models, Biological
  • Perfusion
  • Salt Gland / metabolism*

Substances

  • Bicarbonates
  • Chlorides