Inhibition of voltage-gated K+ channels in dendritic cells by rapamycin

Rapamycin, an inhibitor of the serine/threonine kinase mammalian target of rapamycin (mTOR), is a widely used immunosuppressive drug. Rapamycin affects the function of dendritic cells (DCs), antigen-presenting cells participating in the initiation of primary immune responses and the establishment of immunological memory. Voltage-gated K(+) (Kv) channels are expressed in and impact on the function of DCs. The present study explored whether rapamycin influences Kv channels in DCs. To this end, DCs were isolated from murine bone marrow and ion channel activity was determined by whole cell patch clamp. To more directly analyze an effect of mTOR on Kv channel activity, Kv1.3 and Kv1.5 were expressed in Xenopus oocytes with or without the additional expression of mTOR and voltage-gated currents were determined by dual-electrode voltage clamp. As a result, preincubation with rapamycin (0-50 nM) led to a gradual decline of Kv currents in DCs, reaching statistical significance within 6 h and 50 nM of rapamycin. Rapamycin accelerated Kv channel inactivation. Coexpression of mTOR upregulated Kv1.3 and Kv1.5 currents in Xenopus oocytes. Furthermore, mTOR accelerated Kv1.3 channel activation and slowed down Kv1.3 channel inactivation. In conclusion, mTOR stimulates Kv channels, an effect contributing to the immunomodulating properties of rapamycin in DCs.     

Regulation of the Na+/K+ ATPase by Klotho

Klotho-hypomorphic (Klotho(hm)) mice suffer from renal salt wasting and hypovolemia despite hyperaldosteronism. The present study explored the effect of Klotho on renal Na(+)/K(+) ATPase activity. According to immunohistochemistry and confocal microscopy Na(+)/K(+) ATPase protein abundance in isolated collecting ducts was lower in Klotho(hm) mice than in their wild type littermates (Klotho(+/+)). Analysis with dual electrode voltage clamp recording showed that expression of Klotho in Xenopus oocytes increased the Na(+)/K(+) ATPase pump current. Treatment of Xenopus oocytes with Klotho protein similarly increased the pump current. In conclusion, Klotho increases the membrane abundance and activity of the Na(+)/K(+) ATPase. Decreased Na(+)/K(+) ATPase activity could thus contribute to the volume-depletion of klotho(hm) mice.     

Down-Regulation of the Epithelial Na+ Channel ENaC by Janus kinase 2

Janus kinase-2 (JAK2), a signaling molecule mediating effects of various hormones including leptin and growth hormone, has previously been shown to modify the activity of several channels and carriers. Leptin is known to inhibit and growth hormone to stimulate epithelial Na⁺ transport, effects at least partially involving regulation of the epithelial Na⁺ channel ENaC. However, no published evidence is available regarding an influence of JAK2 on the activity of the epithelial Na⁺ channel ENaC. In order to test whether JAK2 participates in the regulation of ENaC, cRNA encoding ENaC was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild type JAK2, gain-of-function ^V617FJAK2 or inactive ^K882EJAK2. Moreover, ENaC was expressed with or without the ENaC regulating ubiquitin ligase Nedd4-2 with or without JAK2, ^V617FJAK2 or ^K882EJAK2. ENaC was determined from amiloride (50 μM)-sensitive current (I _amil) in dual electrode voltage clamp. Moreover, I _amil was determined in colonic tissue utilizing Ussing chambers. As a result, the I _amil in ENaC-expressing oocytes was significantly decreased following coexpression of JAK2 or ^V617FJAK2, but not by coexpression of ^K882EJAK2. Coexpression of JAK2 and Nedd4-2 decreased I _amil in ENaC-expressing oocytes to a larger extent than coexpression of Nedd4-2 alone. Exposure of ENaC- and JAK2-expressing oocytes to JAK2 inhibitor AG490 (40 μM) significantly increased I _amil. In colonic epithelium, I _amil was significantly enhanced by AG490 pretreatment (40 μM, 1 h). In conclusion, JAK2 is a powerful inhibitor of ENaC.     

Upregulation of KCNQ1/KCNE1 K+ channels by Klotho

Klotho is a transmembrane protein expressed primarily in kidney, parathyroid gland, and choroid plexus. The extracellular domain could be cleaved off and released into the systemic circulation. Klotho is in part effective as β-glucuronidase regulating protein stability in the cell membrane. Klotho is a major determinant of aging and life span. Overexpression of Klotho increases and Klotho deficiency decreases life span. Klotho deficiency may further result in hearing loss and cardiac arrhythmia. The present study explored whether Klotho modifies activity and protein abundance of KCNQ1/KCNE1, a K⁺ channel required for proper hearing and cardiac repolarization. To this end, cRNA encoding KCNQ1/KCNE1 was injected in Xenopus oocytes with or without additional injection of cRNA encoding Klotho. KCNQ1/KCNE1 expressing oocytes were treated with human recombinant Klotho protein (30 ng/ml) for 24 h. Moreover, oocytes which express both KCNQ1/KCNE1 and Klotho were treated with 10 µM DSAL (D-saccharic acid-1,4-lactone), a β-glucuronidase inhibitor. The KCNQ1/KCNE1 depolarization-induced current (I_Ks) was determined utilizing dual electrode voltage clamp, while KCNQ1/KCNE1 protein abundance in the cell membrane was visualized utilizing specific antibody binding and quantified by chemiluminescence. KCNQ1/KCNE1 channel activity and KCNQ1/KCNE1 protein abundance were upregulated by coexpression of Klotho. The effect was mimicked by treatment with human recombinant Klotho protein (30 ng/ml) and inhibited by DSAL (10 µM). In conclusion, Klotho upregulates KCNQ1/KCNE1 channel activity by 'mainly' enhancing channel protein abundance in the plasma cell membrane, an effect at least partially mediated through the β-glucuronidase activity of Klotho protein.     

Regulation of the Ca2+ Channel TRPV6 by the Kinases SGK1, PKB/Akt, and PIKfyve

The serum- and glucocorticoid-inducible kinase SGK1 and the protein kinase PKB/Akt presumably phosphorylate and, by this means, activate the mammalian phosphatidylinositol-3-phosphate-5-kinase PIKfyve (PIP5K3), which has in turn been shown to regulate transporters and channels. SGK1-regulated channels include the Ca²⁺ channel TRPV6, which is expressed in a variety of epithelial and nonepithelial cells including tumor cells. SGK1 and protein kinase B PKB/Akt foster tumor growth. The present study thus explored whether TRPV6 is regulated by PIKfyve. TRPV6 was expressed in Xenopus laevis oocytes with or without additional coexpression of constitutively active ^S422DSGK1, constitutively active ^T308D,S473DPKB, wild-type PIKfyve, and ^S318APIKfyve lacking the SGK1 phosphorylation site. TRPV6 activity was determined from the current (I_Ca) resulting from TRPV6-induced Ca²⁺ entry and subsequent activation of Ca²⁺-sensitive endogenous Cl^? channels. TRPV6 protein abundance in the cell membrane was determined utilizing immunohistochemistry and Western blotting. In TRPV6-expressing oocytes I_H was increased by coexpression of ^S422DSGK1 and by ^T308D,S473DPKB. Coexpression of wild-type PIKfyve further increased I_H in TRPV6 + ^S422DSGK1-expressing oocytes but did not significantly modify I_Ca in oocytes expressing TRPV6 alone. ^S318APIKfyve failed to significantly modify I_Ca in the presence and absence of ^S422DSGK1. ^S422DSGK1 increased the TRPV6 protein abundance in the cell membrane, an effect augmented by additional expression of wild-type PIKfyve. We conclude that PIKfyve participates in the regulation of TRPV6.     

Regulation of Na(+)-coupled glucose carrier SGLT1 by human papillomavirus 18 E6 protein

Tumor cells utilize preferably glucose for energy production. They accomplish cellular glucose uptake in part through Na⁺-coupled glucose transport mediated by SGLT1 (SLC5A1). This study explored the possibility that the human papillomavirus 18 E6 protein HPV18 E6 (E6) participates in the stimulation of SGLT1 activity. E6 is one of the two major oncoproteins of high-risk human papillomaviruses, which are the causative agent for cervical carcinoma. According to Western blotting, SGLT1 is expressed in the HPV18-positive cervical carcinoma cell line HeLa. To explore whether E6 affects SGLT1 activity, SGLT1 was expressed in Xenopus oocytes with and without E6 and electrogenic glucose transport determined by dual electrode voltage clamp. In SGLT1-expressing oocytes, but not in oocytes injected with water or expressing E6 alone, glucose triggered a current (I_g). I_g was significantly increased by coexpression of E6 but not by coexpression of E2. According to chemiluminescence and confocal microscopy, coexpression of E6 significantly increased the SGLT1 protein abundance in the cell membrane. The decay of I_g following inhibition of carrier insertion by Brefeldine A (5 μM) was not significantly affected E6 coexpression. Accrodingly, E6 was not effective by increasing carrier protein stability in the membrane. In conclusion, HPV18 E6 oncoprotein participates in the upregulation of SGLT1.     

Perceived Feasibility,Acceptability, and Cultural Adaptation for a Mental Health Intervention in Rural Haiti

Culture, Medicine, and Psychiatry - Mental healthcare is largely unavailable throughout Haiti, particularly in rural areas. The aim of the current study is to explore perceived feasibility,...     

Cardiovascular autonomic response to food ingestion in patients with gastritis: a comparison between Helicobacter pylori-positive and -negative patients

BACKGROUND: Feeding evokes a cardiovascular response associated to an increased sympathetic drive. The role of the parasympathetic component in this regard is less clear. Improvement of postprandial vasovagal complaints after Helicobacter pylori eradication in three cases led us to assess autonomic response to feeding in H. pylori-positive patients in search for an exacerbated parasympathetic response. MATERIAL AND METHODS: Patients with mild or moderate chronic histologic gastritis were studied. Subjects with the same diagnosis but testing negative for H. pylori were used as controls. Noninvasive cardiovascular tests were applied before and after feeding. RESULTS: On sympathetic tests, standing postprandial blood pressure was lower than preprandially in 5/12 H. pylori-positive patients and in 0/9 controls, p = .045. Resting postprandial BP on handgrip test was significantly lower than preprandially only in H. pylori-positive patients (71 +/- 8 versus 76 +/- 6 mmHg, p = .0068). Regarding parasympathetic tests, the 4-s unloaded exercise revealed greater initial heart rate response to unloaded cycling after feeding than preprandially again only in H. pylori-positive patients (1.40 +/- 0.20 versus 1.33 +/- 0.17, p = .0195). On tests influenced by both branches of the autonomic system, a difference was seen in the chronotropic response to handgrip. Postprandial heart rate on effort of H. pylori-positive patients was not higher than preprandially in contrast to controls [intervals between 2 consecutive R waves on electrocardiogram (R-R intervals) of 666 +/- 39 versus 685 +/- 62 ms, p = .0195], suggesting blunted sympathetic activation in the former. CONCLUSION: Supporting the observations that motivate the study, our findings indicate blunted sympathetic reactivity and exacerbated vagal response to feeding in H. pylori-positive patients.