Role of Kir4.1/Kir5.1 in mediating Angiotensin-II (Ang-II)-induced stimulation of thiazide-sensitive Na-Cl cotransporter.

Background: Angiotensin-II (Ang-II) perfusion stimulates Kir4.1/Kir5.1 in the distal-convoluted-tubule (DCT) and thiazide-sensitive Na-Cl-cotransporter (NCC). However, the role of Kir4.1/Kir5.1 in mediating the effect of Ang-II on NCC is not understood. Methods: We used immunoblotting and patch-clamp-experiments to examine whether Ang-II-induced stimulation of NCC is achieved by activation of Kir4.1/Kir5.1 of the DCT using kidney-renal-tubule-specific AT1aR-knockout (Ks-AT1aR-KO), Ks-Kir4.1-knockout and the corresponding wild-type mice. Results: Ang-II perfusion for 1, 3 and 7 days progressively increased phosphor-NCC (pNCC) and total-NCC (tNCC) expression and the effect of Ang-II-perfusion on pNCC and tNCC was abolished in Ks-AT1aR-KO. Ang-II perfusion for 1-day robustly stimulates Kir4.1/Kir5.1 in the late DCT (DCT2) and to a lesser degree in the early DCT (DCT1), an effect was absent in Ks-AT1aR-KO mice. However, Ang-II perfusion for 7-days did not further stimulate Kir4.1/Kir5.1 in the DCT2 and only modestly increased Kir4.1/Kir5.1-mediated K + currents in DCT1. Deletion of Kir4.1 not only significantly decreased the expression of pNCC and tNCC but also abolished the effect of 1-day Ang-II perfusion on the expression of phospho-with-no-lysine-kinase-4 (pWNK4), phosphor-ste-20-proline-alanine-rich-kinase (pSPAK), pNCC and tNCC. However, 7-days Ang-II perfusion was still able to significantly stimulate the expression of pSPAK, pWNK4, pNCC and tNCC, and increased thiazide-induced natriuresis in kidney-tubule-specific Kir4.1 knockout (Ks-Kir4.1 KO) mice without obvious changes in K + channel activity in the DCT. Conclusions: Short-term Ang-II induced stimulation of pWNK4, pSPAK and pNCC depends on Kir4.1/Kir5.1 activity. However, long-term Ang-II is able to directly stimulate pWNK4, pSPAK and pNCC by a Kir4.1/Kir5.1 independent mechanism.

Role of calcineurin in regulating renal potassium (K+) excretion: Mechanisms of calcineurin inhibitor-induced hyperkalemia.

Calcineurin, protein phosphatase 2B (PP2B) or protein phosphatase 3 (PP3), is a calcium-dependent serine/threonine protein phosphatase. Calcineurin is widely expressed in the kidney and regulates renal Na+ and K+ transport. In the thick ascending limb, calcineurin plays a role in inhibiting NKCC2 function by promoting the dephosphorylation of the cotransporter and an intracellular sorting receptor, called sorting-related-receptor-with-A-type repeats (SORLA), is involved in modulating the effect of calcineurin on NKCC2. Calcineurin also participates in regulating thiazide-sensitive NaCl-cotransporter (NCC) in the distal convoluted tubule. The mechanisms by which calcineurin regulates NCC include directly dephosphorylation of NCC, regulating Kelch-like-3/CUL3 E3 ubiquitin-ligase complex, which is responsible for WNK (with-no-lysin-kinases) ubiquitination, and inhibiting Kir4.1/Kir5.1, which determines NCC expression/activity. Finally, calcineurin is also involved in regulating ROMK (Kir1.1) channels in the cortical collecting duct and Cyp11 2 expression in adrenal zona glomerulosa. In summary, calcineurin is involved in the regulation of NKCC2, NCC, and inwardly rectifying K+ channels in the kidney, and it also plays a role in modulating aldosterone synthesis in adrenal gland, which regulates epithelial-Na+-channel expression/activity. Thus, application of calcineurin inhibitors (CNIs) is expected to abrupt calcineurin-mediated regulation of transepithelial Na+ and K+ transport in the kidney. Consequently, CNIs cause hypertension, compromise renal K+ excretion, and induce hyperkalemia.

[Recording and identification of depolarization-activated current in intercalated cells].

The depolarization-activated current of intercalated cells in the distal nephron was detected for the first time, and the type of ion channel mediating the current was identified based on electrophysiological and pharmacological properties. The whole-cell current of distal nephron in kidney of C57BL/6J mice was recorded by Axon MultiClamp 700B patch-clamp system, and the effects of several K+ channel inhibitors on the depolarization-activated current in intercalated cells were observed. In addition, the immunofluorescence technique was used to investigate the localization of the channel in intercalated cells. The results showed that when K+ concentration of the bath solution was equal to intracellular fluid (140 mmol/L K+), the depolarization-activated current could be recorded in intercalated cells, but this current was not observed in the principal cells. The depolarization-activated current detected in the intercalated cells could be blocked by Kv4.1 inhibitors. The immunofluorescence experiment showed that the fluorescence of Kv4.1 protein was only present in intercalated cells and not observed in principal cells. Kv4.1 protein immunofluorescence was observed in the luminal and basolateral membrane of intercalated cells, but the fluorescence intensity of luminal membrane was higher than that of basolateral membrane. We conclude that the depolarization-activated current detected in intercalated cells is mediated by Kv4.1 and this channel is mainly expressed in the luminal membrane of intercalated cells.

[A method of acutely isolating rat dorsal root ganglion neurons for patch-clamp study of single-channel].

OBJECTIVE: To establish a method of acutely isolating dorsal root ganglion (DRG) neurons for patch clamp study of single-channel. METHODS: DRG neurons of rats were acutely isolated by enzymatic digestion and mechanical blowing. RESULTS: The acutely isolated DRG cells were easy to form the higher sealing resistance (> 5G Omega), which lowered noise level, so that pA-level single channel currents could be recorded. CONCLUSION: The acutely isolated DRG neurons in this study are an ideal for patch-clamp study of single-channel.