Characteristics of acid extrusion from Chinese hamster ovary cells expressing different prostaglandin EP receptors

Acid extrusion responses to prostaglandin E2 were investigated in Chinese hamster ovary (CHO) cells heterologously expressing human EP1, EP2, and EP3I receptors (hEP1, hEP2 and hEP3I) by using a microphysiometer that detected small pH changes in the extracellular microenvironment. In the cells expressing hEP1, which is known to increase intracellular Ca2+, prostaglandin E2 (1 and 10 nM) slowly accelerated acid extrusion, but at higher concentrations an initial transient phase (approximately 5 times greater than the basal acidification) overlapped the slowly developing phase. In contrast, the cells expressing hEP2, which evokes cAMP production, showed dual responses to prostaglandin E2: an initial reduction followed by an acceleration of acid extrusion. In the cells expressing hEP3I, which is known to produce both a decrease in cAMP and a modest increase in intracellular Ca2+, acid extrusion was gradually accelerated by prostaglandin E2 and reached a plateau at around 2 min. Elimination of extracellular Ca2+ diminished the responses to prostaglandin E2 in hEP1 cells, but had little effect on the responses in hEP2 and hEP3I cells. Forskolin mimicked the dual effects of prostaglandin E2 observed in the hEP2 cells. Pretreatment with pertussis toxin inhibited the response to prostaglandin E2 in hEP3I cells, but the responses in hEP1 and hEP2 cells were not affected. Na+/H+ exchanger (NHE) inhibitors (EIPA and HOE642) suppressed all the responses induced by prostaglandin E2 in hEP1, hEP2, and hEP3I cells. These results suggest that EP receptor subtypes regulate acid extrusion mainly via NHE-1 through distinct signal transduction pathways in CHO cells.