Evidence for a [formula omitted] exchange system in the mammalian lens

Abstract

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 m m) and the second accompanies exposure to an acidified propionate (20 m m) 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 HCO 3 − . In the absence of external Cl −, the presence of HCO 3 − (16 m m) resulted in an increase in 36Cl efflux during internal acidification. In the absence of internal acidification, the addition of 0·1 m m dibutyrylcAMP or 0·5 m m IBMX to the external medium produced a rapid increase in 36Cl − efflux. This stimulation was reduced by 0·2 m m 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 − HCO 3 − exchange mechanism is activated when the lens internal pH falls and further that cAMP may play a role in regulating this mechanism.