Evidence for a Na(+)-Cl(-)-H(+)-HCO3- exchange system in the mammalian lens.
36Cl- efflux was studied in the isolated rat lens under two conditions that are known to decrease internal pH. The first follows exposure to a pulse of ammonium chloride (50 mM) and the second accompanies exposure to an acidified propionate (20 mM) solution. Under acidifying conditions, a stimulation in 36Cl- efflux was observed, that was abolished on removing external Na+ and also on removing external Cl- and HCO3-. In the absence of external Cl-, the presence of HCO3- (16 mM) resulted in an increase in 36Cl- efflux during internal acidification. In the absence of internal acidification, the addition of 0.1 mM dibutyrylcAMP or 0.5 mM IBMX to the external medium produced a rapid increase in 36Cl- efflux. This stimulation was reduced by 0.2 mM SITS. Neither cAMP or IBMX had any significant effect on the electrical resistance of the lens membranes. It is suggested that a coupled SITS-sensitive, Na(+)-Cl(-)-H(+)-HCO3- exchange mechanism is activated when the lens internal pH falls and further that cAMP may play a role in regulating this mechanism.
Duncan
G
G
Biomedical Research Centre, School of Biological Sciences, University of East Anglia, Norwich, U.K.
Dart
C
C
Croghan
P C
PC
Gandolfi
S A
SA
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism*; D008839:Microelectrodes; D011422:Propionates / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D008565:Membrane Proteins; D011422:Propionates; D000643:Ammonium Chloride; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; C029658:propionic acid