Bicarbonate and DIDS effects on intracellular potential difference in rabbit ciliary epithelium

A change of [HCO3-] in the solution bathing isolated rabbit ciliary epithelium from 30 mM to 0, or vice versa, resulted in a change of intracellular electrical potential difference (PDI) of 7 mV. Intermediate [HCO3-] (5, 10 and 15 mM) solutions were also tested. No perceivable change of PDI occurred when [HCO3-] changed from 30 to 15 mM. PDI depolarized gradually when [HCO3-] decreased from 30 or 15 mM to 0 mM, but PDI hyperpolarized at a faster rate when [HCO3-] increased from 0 to 15 or 30 mM. The amount of change of PDI from 15 to 5 mM, or vice versa, and from 10 to 0 mM or vice versa, was 4 mV. The stilbene, DIDS (10(-4) M), hyperpolarized the PDI in HCO3(-)-rich solutions. The response of DIDS was reduced in HCO3(-)-free medium and inhibited in Cl(-)-free solution. The results suggest the existence of an electrogenic bicarbonate transport or Na+/HCO3- cotransport system.