Low pH stimulates vasopressin V2 receptor promoter activity and enhances downregulation induced by V1a receptor stimulation.

Arginine vasopressin (AVP) plays a key role in the urine concentration mechanism via the vasopressin V2 receptor (V2R) and aquaporin 2 (AQP2) in the kidney. It is well known that V2R is localized on the basolateral side and the V1a receptor (V1aR) is distributed on the luminal side of the collecting ducts. Previously, we reported an increase of V1aR mRNA and a decrease of V2R mRNA in the collecting ducts under chronic metabolic acidosis. However, the regulatory mechanism of V2R in acidic conditions has not yet been determined. In the present study, we investigated the effect of changes in pH on V2R promoter activity, using the LLC-PK(1) cell line stably expressing rat V1aR (LLC-PK(1)/rV1aR). The rV2R promoter activity was significantly increased at 12 h after the incubation in low-pH conditions, which was sustained for 24 h. mRNA and protein expressions of V2R were also increased in low-pH conditions. V1aR stimulation suppressed rV2R promoter activity in a pH-dependent manner. PKA and JNK inhibitors suppressed rV2R promoter activity in both neutral and low-pH conditions without FBS. However, a JNK inhibitor prevented the increase of V2R promoter activity only in low-pH conditions in the presence of FBS. In summary, V2R expression is increased at transcriptional, mRNA, and protein levels in LLC-PK(1)/rV1aR cells under low-pH conditions. Acidic condition-induced V2R enhancement was suppressed by V1aR stimulation, suggesting the crucial role of V1aR in water and electrolyte homeostasis in acidosis.