Search

We previously reported that a deficiency in the vasopressin V1a receptor (V1aR) results in type 4 renal tubular acidosis, which suggests that vasopressin exerts direct effects on the physiological actions of aldosterone. We investigated the role of vasopressin for nucleocytoplasmic transport of mineralocorticoid receptor (MR) in the intercalated cells. Vasopressin V1aR-deficient (V1aR−/−) mice showed largely decreased expression of MR and 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) in the medulla of the kidney, which was partially ameliorated by fludrocortisone treatment. The incubation of IN-IC cells, an intercalated cell line established from temperature-sensitive SV40 large T antigen-expressing rats, with aldosterone or vasopressin increased the nuclear-to-cytoplasmic ratio of the MR from 11.2 to 47.2% and from 18.7 to 61.2%, respectively, in 30 min without any changes in MR expression from the whole cell extract. The immunohistochemistry analysis of the IN-IC cells revealed the nuclear accumulation of MRs after a 30-min incubation with aldosterone or vasopressin. These effects were accompanied by an increase in regulator of chromosome condensation-1 (RCC-1) due to aldosterone and a decrease in Ran GTPase-activating protein 1 (Ran Gap1) due to vasopressin. RNA interference against V1aR abolished the nuclear accumulation of MR induced by aldosterone or vasopressin. Vasopressin increased PKCα and -β1 expression, and aldosterone increased PKCδ and -ζ expression, but these effects were abolished with a V1aR knockdown. These results suggest that vasopressin directly regulates the nucleocytoplasmic transport of MRs via the V1aR in the intercalated cells of the collecting ducts.

Arginine vasopressin (AVP) and hypertonicity in the renal medulla play a major role in the urine concentration mechanism. Previously, we showed that rat vasopressin V2 receptor (rV2R) promoter activity was increased by vasopressin V2R stimulation and decreased by vasopressin V1a receptor (V1aR) stimulation in a LLC-PK1 cell line stably expressing rat V1aR (LLC-PK1/rV1aR). In the present study, we investigated the effects of hypertonicity on the rV2R promoter activity and on the suppression of rV2R promoter activity by V1aR stimulation in LLC-PK1/rV1aR cells. rV2R promoter activity was increased in NaCl- or mannitol-induced hypertonicity. The hypertonicity-responsive site in the rV2R promoter region was limited to 10 bp, including the Sp1 motif. The increase of V2R promoter activity by hypertonicity was significantly inhibited by a JNK inhibitor (SP600125) and PKA inhibitor (H89). In contrast, rV2R promoter activity was remarkably suppressed by V1aR stimulation in the hypertonic condition rather than in the isotonic condition. The AVP-stimulated intracellular Ca2+ concentration was increased in the hypertonic condition, suggesting the functional activation of V1aR by hypertonicity. In conclusion, 1) V2R promoter activity is increased by hypertonicity via the JNK and PKA pathways, 2) suppression of V2R expression by the V1aR-Ca2+ pathway is enhanced by hypertonicity, and 3) hypertonicity enhances the V1aR-Ca2+ pathway. The counteractivity of V2R and V1aR could be required to maintain minimum urine volume in the dehydrated state.