Anorexic effect of K+ channel blockade in mesenteric arterial smooth muscle and intestinal epithelial cells

Cl- induces endothelium-dependent mesenteric arteriolar vasorelaxation through the NKCC1/TRPV4/NCX axis

AIMS

Although absorbed NaCl increases intestinal blood flow to facilitate absorption and transportation, it is unclear if it can directly mediate mesenteric arterial relaxation. We aimed to investigate and test our hypothesis that Cl- induces mesenteric arterial vasorelaxation via endothelium-dependent hyperpolarization (EDH).

MAIN METHODS

We used wire myograph to study NaCl-induced vasorelaxation of mesenteric arteries isolated from mice. Cl-, Ca2+ and K+ imaging was performed in human vascular endothelial cells pre-treated with pharmacological agents.

KEY FINDINGS

The Cl- concentration-dependently induced vasorelaxation of mesenteric arteries likely through EDH. The Cl--induced vasorelaxation was attenuated in TRPV4 KO mice and inhibited by selective blockers of Na+-K+-2Cl- cotransporter 1 (NKCC1) (bumetanide, 10 μM), transient receptor potential vanilloid 4 (TRPV4) (RN-1734, 40 μM), and small conductance Ca2+-activated K+ channels (SKCa) (apamin, 3 μM)/ intermediate conductance Ca2+-activated K+ channels (IKCa) (TRAM-34, 10 μM) and myoendothelial gap junction (18α-glycyrrhetinic acid, 10 μM), but enhanced by a selective activator of IKCa/SKCa (SKA-31, 0.3 μM). Cl- decreased intracellular K+ concentrations in endothelial cells, which was reversed by apamin (200 nM) plus TRAM-34 (500 nM). Extracellular Cl- raised intracellular Cl- concentrations in endothelial cells, which was attenuated by bumetanide (10 μM). Finally, Cl- induced a transient Ca2+ signaling via TRPV4 in endothelial cells, which became sustained when the Ca2+ exit mode of Na+-Ca2+ exchanger (NCX) was blocked.

SIGNIFICANCE

Cl- induces a pure EDH-mediated vasorelaxation of mesenteric arteries through activation of endothelial NKCC1/TRPV4/NCX axis. We have provided a novel insight into the role of Cl--induced vasorelaxation via EDH mechanism.

Assessment of redox state and biochemical parameters of salivary glands in rats treated with anti-obesity drug sibutramine hydrochloride

OBJECTIVES

To investigate the effects of anti-obesity drug sibutramine hydrochloride (SB) on redox state and biochemical parameters in the salivary glands.

MATERIALS AND METHODS

Adult male Wistar rats were randomly divided into the following groups (n = 8 per group): control rats treated with vehicle (C) and rats treated with SB (10 mg/kg/day) by intragastric gavage for 28 days. The parotid (PG) and submandibular (SMG) glands were processed using histomorphometric analysis, and total protein, amylase, mucin, and oxidative damage to lipids were determined by measuring the formation of thiobarbituric acid reactive substances (TBARS), total antioxidant capacity (TAC), uric acid (UA), total glutathione (tGSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), and AKT phosphorylation.

RESULTS

SB decreased the acinar area, and increased the stromal area in PG, while no effect on the morphometric parameters was observed in SMG. SB also increased oxidative damage to lipids (TBARs). The SB group showed lower total protein, amylase, TAC, UA, tGSH, SOD, CAT, and GPx than the C group in PG, while in SMG, SB decreased total protein, mucin, tGSH, SOD, CAT, and GPx. However, increased AKT phosphorylation observed in both salivary glands suggests that SB exerts low-intensity oxidative stress.

CONCLUSIONS

SB impaired enzymatic and non-enzymatic antioxidant defenses in the salivary glands of rats.

CLINICAL RELEVANCE

Chronic treatment with SB could mitigate salivary gland dysfunction due to disturbance of redox state.

GLUT3 as an Intersection of Glycerophospholipid Metabolism and the Innate Immune Response to Candida albicans

Immune cells can optimize the management of metabolic resources to balance their energy requirements in order to regulate immune responses. The interconnection between immunometabolism and fungal infections is becoming increasingly apparent. Using proteome and metabolome assays, we found that stimulation of primary human monocytes by Candida albicans was accompanied by upregulation of glucose transporter 3 (GLUT3) and activation of the glycerophospholipid metabolism pathway. Upregulated GLUT3 expression has been preliminarily confirmed in monocytes from patients with C. albicans bloodstream infection. Our findings support the importance of GLUT3 in the complex network of glycerophospholipid metabolism and the innate immune responses against C. albicans. In summary, this study might contribute to decipher the regulatory mechanism between the monocyte metabolic reprogramming and innate immune response and reveal potential targets for the antifungal treatments.

Potassium channels in intestinal epithelial cells and their pharmacological modulation: a systematic review

Several potassium channels (KCs) have been described throughout the gastrointestinal tract. Notwithstanding, their contribution to both physiologic and pathophysiologic conditions, as inflammatory bowel disease (IBD), remains underexplored. Therefore, we aim to systematically review, for the first time, the evidence on the characteristics and modulation of KCs in intestinal epithelial cells (IECs). PubMed, Scopus, and Web of Science were searched to identify studies focusing on KCs and their modulation in IECs. The included studies were assessed using a reporting inclusiveness checklist. From the 745 identified records, 73 met the inclusion criteria; their reporting inclusiveness was moderate-high. Some studies described the physiological role of KCs, while others explored their importance in pathological settings. Globally, in IBD animal models, apical K_Ca1.1 channels, responsible for luminal secretion, were upregulated. In human colonocytes, basolateral K_Ca3.1 channels were downregulated. The pharmacological inhibition of K_2P and K_v influenced intestinal barrier function, promoting inflammation. Evidence suggests a strong association between KCs expression and secretory mechanisms in human and animal IECs. Further research is warranted to explore the usefulness of KC pharmacological modulation as a therapeutic target.

Nutrient-induced hyperosmosis evokes vasorelaxation via TRPV1 channel-mediated, endothelium-dependent, hyperpolarisation in healthy and colitis mice

BACKGROUND AND PURPOSE

In humans, blood flow in the mesenteric circulation is greatly increased after meals, but the mechanisms underlying postprandial mesenteric vasorelaxation induced by nutrients and whether this process is involved in the pathogenesis of colitis, are not well understood. Here we have studied the direct actions of nutrients on mesenteric arterial tone and the underlying molecular mechanisms in healthy and colitis mice.

EXPERIMENTAL APPROACH

Colitis in C57BL/6 mice was induced with dextran sodium sulphate. Nutrient-induced vasorelaxation of mesenteric arterioles from humans and mice was studied with wire myograph assays. Ca²⁺ and Na⁺ imaging were performed in human vascular endothelial cells and vascular smooth muscle cells, using selective pharmacological agents and shRNA knockdown of TRPV1 channels.

KEY RESULTS

Glucose, sodium and mannitol concentration-dependently induced endothelium-dependent relaxation of human and mouse mesenteric arterioles via hyperosmotic action,. Hyperosmosis-induced vasorelaxation was almost abolished by selective blockers for TRPV1, IK_Ca and SK_Ca channels. Glucose markedly stimulated Ca²⁺ influx through endothelial TRPV1 channels, an effect attenuated by selective blockers and shRNA knockdown of TRPV1 channels. Capsaicin synergised the glucose-induced vasorelaxation. Nutrient-induced hyperosmosis also activated Na⁺ /K⁺ -ATPase and the Na/Ca exchanger (NCX) to decrease [Ca²⁺ ]_i in VSMCs. Glucose-induced vasorelaxation was impaired in mouse colitis.

CONCLUSION AND IMPLICATIONS

Nutrient-induced hyperosmosis evoked endothelium-dependent mesenteric vasorelaxation via the TRPV1/Ca²⁺ / endothelium-dependent hyperpolarisation pathway to increase normal mucosal perfusion, which is impaired in our model of colitis. The TRPV1/Ca²⁺ / endothelium-dependent hyperpolarisation pathway could provide novel drug targets for gastrointestinal diseases with hypoperfusion, such as chronic colitis and mesenteric ischaemia.

Near-infrared light control of membrane potential by an electron donor-acceptor linked molecule

Near-infrared (NIR) light control of living cellular activities is a highly desired technique for living cell manipulation because of its advantage of high penetrability towards living tissue. In this study, (π-extended porphyrin)-fullerene linked molecules are designed and synthesized to achieve NIR light control of the membrane potential. A donor-(π-extended porphyrin)-acceptor linked molecule exhibited the formation of the charge-separated state with a relatively long lifetime (0.68 μs) and a moderate quantum yield (27-31%). The hydrophilic trimethylammonium-linked triad molecule successfully altered PC12 cells' membrane potential via photoinduced intramolecular charge separation.

Sound Localization in Preweanling Mice Was More Severely Affected by Deleting the Kcna1 Gene Compared to Deleting Kcna2, and a Curious Inverted-U Course of Development That Appeared to Exceed Adult Performance Was Observed in All Groups

The submillisecond acuity for detecting rapid spatial and temporal fluctuations in acoustic stimuli observed in humans and laboratory animals depends in part on select groups of auditory neurons that preserve synchrony from the ears to the binaural nuclei in the brainstem. These fibers have specialized synapses and axons that use a low-threshold voltage-activated outward current, IKL, conducted through Kv1 potassium ion channels. These are in turn coupled with HCN channels that express a mixed cation inward mixed current, IH, to support precise synchronized firing. The behavioral evidence is that their respective Kcna1 or HCN1 genes are absent in adult mice; the results are weak startle reflexes, slow responding to noise offsets, and poor sound localization. The present behavioral experiments were motivated by an in vitro study reporting increased IKL in an auditory nucleus in Kcna2-/- mice lacking the Kv1.2 subunit, suggesting that Kcna2-/- mice might perform better than Kcna2+/+ mice. Because Kcna2-/- mice have only a 17-18-day lifespan, we compared both preweanling Kcna2-/- vs. Kcna2+/+ mice and Kcna1-/- vs. Kcna1+/+ mice at P12-P17/18; then, the remaining mice were tested at P23/P25. Both null mutant strains had a stunted physique, but the Kcna1-/- mice had severe behavioral deficits while those in Kcna2-/- mice were relatively few and minor. The in vitro increase of IKL could have resulted from Kv1.1 subunits substituting for Kv1.2 units and the loss of the inhibitory "managerial" effect of Kv1.2 on Kv1.1. However, any increased neuronal synchronicity that accompanies increased IKL may not have been enough to affect behavior. All mice performed unusually well on the early spatial tests, but then, they fell towards adult levels. This unexpected effect may reflect a shift from summated independent monaural pathways to integrated binaural processing, as has been suggested for similar observations for human infants.

Different functional roles for K+ channel subtypes in regulating small intestinal glucose and ion transport

Although K⁺ channels are important in mediating the driving force for colonic ion transport, their role in small intestinal transport is poorly understood. To investigate this, small intestinal short circuit currents (I_sc ) and HCO₃ ^- secretion were measured in mice, and intracellular pH (pH_i) was measured in small intestinal epithelial SCBN cells. The expression and location of Kv subtypes were verified by RT-PCR, western blotting and immunohistochemistry. Diabetic mice were also used to investigate the role of Kv subtypes in regulating intestinal glucose absorption. We found that K_V7.1 is not involved in duodenal ion transport, while K_Ca3.1 selectively regulates duodenal I_sc and HCO₃ ^- secretion in a Ca²⁺-mediated but not cAMP-mediated manner. Blockade of K_Ca3.1 increased the rate of HCO₃ ^- fluxes via cystic fibrosis transmembrane conductance regulator (CFTR) channels in SCBN cells. Jejunal I_sc was significantly stimulated by glucose, but markedly inhibited by 4-aminopyridine (4-AP) and tetraethylammonium (TEA). Moreover, both Kv1.1 and Kv1.3 were expressed in jejunal mucosae. Finally, 4-AP significantly attenuated weight gain of normal and diabetic mice, and both 4-AP and TEA significantly lowered blood glucose of diabetic mice. This study not only examines the contribution of various K⁺ channel subtypes to small intestinal epithelial ion transport and glucose absorption, but also proposes a novel concept for developing specific K⁺ channel blockers to reduce weight gain and lower blood glucose in diabetes mellitus.

KV channels and the regulation of vascular smooth muscle tone

VSMCs in resistance arteries and arterioles express a diverse array of K_V channels with members of the K_V 1, K_V 2 and K_V 7 families being particularly important. Members of the K_V channel family: (i) are highly expressed in VSMCs; (ii) are active at the resting membrane potential of VSMCs in vivo (-45 to -30 mV); (iii) contribute to the negative feedback regulation of VSMC membrane potential and myogenic tone; (iv) are activated by cAMP-related vasodilators, hydrogen sulfide and hydrogen peroxide; (v) are inhibited by increases in intracellular Ca²⁺ and vasoconstrictors that signal through G_q -coupled receptors; (vi) are involved in the proliferative phenotype of VSMCs; and (vii) are modulated by diseases such as hypertension, obesity, the metabolic syndrome and diabetes. Thus, K_V channels participate in every aspect of the regulation of VSMC function in both health and disease.

AMP-activated protein kinase: a therapeutic target in intestinal diseases

Adenosine monophosphate (AMP)-activated protein kinase (AMPK), a highly conserved energy sensor, has a crucial role in cardiovascular, neurodegenerative and inflammatory diseases, as well as in cancer and metabolic disorders. Accumulating studies have demonstrated that AMPK activation enhances paracellular junctions, nutrient transporters, autophagy and apoptosis, and suppresses inflammation and carcinogenesis in the intestine, indicating an essential role of AMPK in intestinal health. AMPK inactivation is an aetiological factor in intestinal dysfunctions. This review summarizes the favourable outcomes of AMPK activation on intestinal health, and discusses AMPK as a potential therapeutic target for intestinal diseases.

Alterations of voltage-dependent K(+) channels in the mesenteric artery during the early and chronic phases of diabetes

This study investigated the alteration of voltage-dependent K(+) (Kv) channels in mesenteric arterial smooth muscle cells from control (Long-Evans Tokushima Otsuka [LETO]) and diabetic (Otsuka Long-Evans Tokushima Fatty [OLETF]) rats during the early and chronic phases of diabetes. We demonstrated alterations in the mesenteric Kv channels during the early and chronic phase of diabetes using the patch-clamp technique, the arterial tone measurement system, and RT-PCR in Long-Evans Tokushima (LETO; for control) and Otsuka Long-Evans Tokushima Fatty (OLETF; for diabetes) type 2 diabetic model rats. In the early phase of diabetes, the amplitude of mesenteric Kv currents induced by depolarizing pulses was greater in OLETF rats than in LETO rats. The contractile response of the mesenteric artery induced by the Kv inhibitor, 4-aminopyridine (4-AP), was also greater in OLETF rats. The expression of most Kv subtypes- including Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv1.6, Kv2.1, Kv3.2, Kv4.1, Kv4.3, Kv5.1, Kv6.2, Kv8.1, Kv9.3, and Kv10.1-were increased in mesenteric arterial smooth muscle from OLETF rats compared with LETO rats. However, in the chronic phase of diabetes, the Kv current amplitude did not differ between LETO and OLETF rats. In addition, the 4-AP-induced contractile response of the mesenteric artery and the expression of Kv subtypes did not differ between the two groups. The increased Kv current amplitude and Kv channel-related contractile response were attributable to the increase in Kv channel expression during the early phase of diabetes. The increased Kv current amplitude and Kv channel-related contractile response were reversed during the chronic phase of diabetes.

Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters

The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na⁺/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca²⁺]_cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca²⁺ in IEC are regulated by cation channels and transporters, such as Ca²⁺ channels, K⁺ channels, Na⁺/Ca²⁺ exchangers, and Na⁺/H⁺ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes.

Extracellular calcium modulates the inhibitory effect of 4-aminopyridine on Kv current in vascular smooth muscle cells

4-Aminopyridine is widely used as a Kv channel blocker. However, its mechanism of action is still a matter of debate. Extracellular calcium as well as 4-aminopyridine have been reported to interact with the activation kinetics of particular Kv channels. The objective of the present study was to investigate whether extracellular calcium could modulate the inhibition of Kv current by 4-aminopyridine in vascular myocytes. Kv current was recorded by using whole-cell patch-clamp in freshly isolated smooth muscle cells from rat mesenteric artery. Macroscopic properties of Kv current were not affected by change in extracellular calcium from 0 to 2mM. During a 10s depolarizing pulse, 4-aminopyridine inhibited the peak current without affecting the end-pulse current. The concentration-effect curve of 4-aminopyridine was shifted to the left in the presence of 2mM calcium compared to 0 calcium. After 4-aminopyridine washout, current recovery from block was slower in the presence than in the absence of calcium. Inhibition of Kv current by 4-aminopyridine (0.5mM) and the Kv2 blocker stromatoxin (50nM) was additive and stromatoxin did not alter the potentiation of 4-aminopyridine effect by extracellular calcium. These results showed that extracellular calcium modulated the inhibitory potency of 4-aminopyridine on Kv current in vascular myocytes. The component of Kv current that was inhibited by 4-aminopyridine in a calcium-sensitive manner was distinct from Kv2 current.

KV2.1 and electrically silent KV channel subunits control excitability and contractility of guinea pig detrusor smooth muscle

Voltage-gated K(+) (K(V)) channels are implicated in detrusor smooth muscle (DSM) function. However, little is known about the functional role of the heterotetrameric K(V) channels in DSM. In this report, we provide molecular, electrophysiological, and functional evidence for the presence of K(V)2.1 and electrically silent K(V) channel subunits in guinea pig DSM. Stromatoxin-1 (ScTx1), a selective inhibitor of the homotetrameric K(V)2.1, K(V)2.2, and K(V)4.2 as well as the heterotetrameric K(V)2.1/6.3 and K(V)2.1/9.3 channels, was used to examine the role of these K(V) channels in DSM function. RT-PCR indicated mRNA expression of K(V)2.1, K(V)6.2-6.3, K(V)8.2, and K(V)9.1-9.3 subunits in isolated DSM cells. K(V)2.1 protein expression was confirmed by Western blot and immunocytochemistry. Perforated whole cell patch-clamp experiments revealed that ScTx1 (100 nM) inhibited the amplitude of the K(V) current in freshly isolated DSM cells. ScTx1 (100 nM) did not significantly change the steady-state activation and inactivation curves for K(V) current. However, ScTx1 (100 nM) decreased the activation time-constant of the K(V) current at positive voltages. Although our patch-clamp data could not exclude the presence of the homotetrameric K(V)2.1 channels, the biophysical characteristics of the ScTx1-sensitive current were consistent with the presence of heterotetrameric K(V)2.1/silent K(V) channels. Current-clamp recordings showed that ScTx1 (100 nM) did not change the DSM cell resting membrane potential. ScTx1 (100 nM) increased the spontaneous phasic contraction amplitude, muscle force, and muscle tone as well as the amplitude of the electrical field stimulation-induced contractions of isolated DSM strips. Collectively, our data revealed that K(V)2.1-containing channels are important physiological regulators of guinea pig DSM excitability and contractility.

Increased sensitivity of serotonin on the voltage-dependent K+ channels in mesenteric arterial smooth muscle cells of OLETF rats

This study examined the mechanisms of hypertension in diabetes. We investigated the effects of serotonin (5-HT) on voltage-dependent K(+) (Kv) channel activity, vasoconstriction, 5-HT receptor expression levels, and the involvement of protein kinase C (PKC) in mesenteric arteries of Otsuka Long-Evans Tokushima fatty (OLETF) rats compared with Long-Evans Tokushima Otsuka (LETO) rats. Blood pressure, body weight, blood glucose level, and mesenteric arterial wall thickness were greater in OLETF rats. The 5-HT-induced vasoconstriction of mesenteric arteries was greater in OLETF rats than in LETO rats and inhibited by the 5-HT(2A) inhibitor inhibitor, ketanserin. The Kv currents in mesenteric arterial smooth muscle cells (MASMCs), determined using a perforated patch clamp technique, was inhibited by 1 mM 4-AP (42.5 +/- 4.1% vs. 63.5 +/- 2.3% in LETO vs. OLETF rats at +40 mV), but was insensitive to 1 mM TEA and 100 nM iberiotoxin. The inhibition of Kv current by 1 microM 5-HT in MASMCs was greater in OLETF rats than in LETO rats (17.1 +/- 2.2% vs. 33.2 +/- 2.7% in LETO vs. OLETF rats at +40 mV), and the inhibition was prevented by treatment with the PKCalpha- and beta- selective inhibitor, Gö6976. The expression level of 5-HT(2A), but not 5-HT(2B), receptor and the expression levels of total PKC, PKCbeta, and PKCepsilon, but not PKCalpha, were higher in the mesenteric arteries of OLETF rats compared with LETO rats. The enhanced expression of 5-HT(2A) receptor together with PKCbeta may promote mesenteric vasoconstriction and increase vascular resistance in OLETF rats.

Endurance swimming stimulates transepithelial calcium transport and alters the expression of genes related to calcium absorption in the intestine of rats

Endurance impact exercise, e.g., running, is known to enhance the intestinal calcium absorption. However, nonimpact exercise, e.g., swimming, is more appropriate for osteoporotic patients with cardiovascular diseases or disorders of bone and joint, but the effect of swimming on the intestinal calcium transport was unknown. This study, therefore, aimed to investigate the transepithelial calcium transport and the expression of related genes in the intestine of rats trained to swim nonstop 1 h/day, 5 days/wk for 2 wk. We found that endurance swimming stimulated calcium transport in the duodenum, proximal jejunum, and cecum, while decreasing that in the proximal colon. Swimming affected neither the transepithelial potential difference nor resistance. As demonstrated by real-time PCR, the small intestine, especially the duodenum, responded to swimming by upregulating a number of genes related to the transcellular calcium transport, i.e., TRPV5, TRPV6, calbindin-D9k, PMCA1b, and NCX1, and the paracellular calcium transport, i.e., ZO-1, ZO-2, ZO-3, cingulin, occludin, and claudins, as well as nuclear receptor of 1,25(OH)2D3. In contrast, swimming downregulated those genes in the colon. Microarray analysis showed that swimming also altered the expression of duodenal genes related to the transport of several ions and nutrients, e.g., Na+, K+, Cl-, glucose, and amino acids. In conclusion, endurance swimming enhanced intestinal calcium absorption, in part, by upregulating the calcium transporter genes. The present microarray study also provided relevant information for further investigations into the intestinal nutrient and electrolyte transport during nonimpact exercise.

Gene expression profile of duodenal epithelial cells in response to chronic metabolic acidosis

Chronic metabolic acidosis (CMA) affects ion transport, permeability, and metabolism of the intestinal absorptive cells. Most effects of CMA on the intestine are long-term adaptations at genomic level. To identify the CMA-regulated genes, the Illumina's microarray featuring high-performance BeadArray technology was performed on RNA samples from the rat duodenal epithelial cells exposed to long-standing acidemia. After 21 days of CMA, we found 423 transcripts upregulated and 261 transcripts downregulated. Gene ontology analysis suggested effects of CMA on cellular processes, such as cell adhesion, proliferation, fuel metabolism, and biotransformation. Interestingly, 27 upregulated transcripts (e.g., Aqp1, Cacnb1, Atp1a2, Kcnab2, and Slc2a1) and 13 downregulated transcripts (e.g., Slc17a7, Slc9a4, and Slc30a3) are involved in the absorption of water, ions, and nutrients. Some upregulated genes, such as Slc38a5 and Slc1a7 encoding glutamine transporters, may be parts of the total body adaptation to alleviate negative nitrogen balance. Therefore, the present results provided a novel genome-wide information for further investigations of the mechanism of CMA effect on the intestine.

Depolarization and decreased surface expression of K+ channels contribute to NSAID-inhibition of intestinal restitution

Non-steroidal anti-inflammatory drugs (NSAIDs) contribute to gastrointestinal ulcer formation by inhibiting epithelial cell migration and mucosal restitution; however, the drug-affected signaling pathways are poorly defined. We investigated whether NSAID inhibition of intestinal epithelial migration is associated with depletion of intracellular polyamines, depolarization of membrane potential (E(m)) and altered surface expression of K(+) channels. Epithelial cell migration in response to the wounding of confluent IEC-6 and IEC-Cdx2 monolayers was reduced by indomethacin (100 microM), phenylbutazone (100 microM) and NS-398 (100 microM) but not by SC-560 (1 microM). NSAID-inhibition of intestinal cell migration was not associated with depletion of intracellular polyamines. Treatment of IEC-6 and IEC-Cdx2 cells with indomethacin, phenylbutazone and NS-398 induced significant depolarization of E(m), whereas treatment with SC-560 had no effect on E(m). The E(m) of IEC-Cdx2 cells was: -38.5+/-1.8 mV under control conditions; -35.9+/-1.6 mV after treatment with SC-560; -18.8+/-1.2 mV after treatment with indomethacin; and -23.7+/-1.4 mV after treatment with NS-398. Whereas SC-560 had no significant effects on the total cellular expression of K(v)1.4 channel protein, indomethacin and NS-398 decreased not only the total cellular expression of K(v)1.4, but also the cell surface expression of both K(v)1.4 and K(v)1.6 channel subunits in IEC-Cdx2. Both K(v)1.4 and K(v)1.6 channel proteins were immunoprecipitated by K(v)1.4 antibody from IEC-Cdx2 lysates, indicating that these subunits co-assemble to form heteromeric K(v) channels. These results suggest that NSAID inhibition of epithelial cell migration is independent of polyamine-depletion, and is associated with depolarization of E(m) and decreased surface expression of heteromeric K(v)1 channels.

Ketamine blocks voltage-gated K(+) channels and causes membrane depolarization in rat mesenteric artery myocytes

Clinical doses of ketamine typically increase blood pressure, heart rate, and cardiac output. However, the precise mechanism by which ketamine produces these cardiovascular effects remains unclear. The voltage-gated K(+) (K(V)) channel is the major regulator of resting membrane potential (E (m)) and vascular tone in many arteries. Therefore, we sought to evaluate the effects of ketamine on K(V) currents using the standard whole-cell patch clamp recordings in single myocytes, enzymatically dispersed from rat mesenteric arteries. Ketamine [(+/-)-racemic mixture] inhibited K(V) currents reversibly and concentration dependently with a K ( d ) of 566.7 +/- 32.3 microM and Hill coefficient of 0.75 +/- 0.03. The inhibition of K(V) currents by ketamine was voltage independent, and the time courses of channel activation and inactivation were little affected. The effects of ketamine on steady-state activation and inactivation curves were also minimal. Use-dependent inhibition was not observed either. S(+)-ketamine inhibited K(V) currents with similar potency and efficacy as the racemic mixture. The average resting E (m) in rat mesenteric artery myocytes was -44.1 +/- 4.2 mV, and both racemic and S(+)-ketamine induced depolarization of E (m) (15.8 +/- 3.6 and 24.3 +/- 5.0 mV at 100 microM, respectively). We conclude that ketamine induces E (m) depolarization in vascular myocytes by blocking K(V) channels in a state-independent manner, which may contribute to the increased vascular tone and blood pressure produced by this drug under a clinical setting.

Open channel block of A-type, kv4.3, and delayed rectifier K+ channels, Kv1.3 and Kv3.1, by sibutramine

The effects of sibutramine on voltage-gated K+ channel (Kv)4.3, Kv1.3, and Kv3.1, stably expressed in Chinese hamster ovary cells, were investigated using the whole-cell patch-clamp technique. Sibutramine did not significantly decrease the peak Kv4.3 currents, but it accelerated the rate of decay of current inactivation in a concentration-dependent manner. This phenomenon was effectively characterized by integrating the total current over the duration of a depolarizing pulse to +40 mV. The IC50 value for the sibutramine block of Kv4.3 was 17.3 microM. Under control conditions, the inactivation of Kv4.3 currents could be fit to a biexponential function, and the time constants for the fast and slow components were significantly decreased after the application of sibutramine. The association (k+1) and dissociation (k-1) rate constants for the sibutramine block of Kv 4.3 were 1.51 microM-1s-1 and 27.35 s-1, respectively. The theoretical KD value, derived from k-1/k+1, yielded a value of 18.11 microM. The block of Kv4.3 by sibutramine displayed a weak voltage dependence, increasing at more positive potentials, and it was use-dependent at 2 Hz. Sibutramine did not affect the time course for the deactivating tail currents. Neither steady-state activation and inactivation nor the recovery from inactivation was affected by sibutramine. Sibutramine caused the concentration-dependent block of the Kv1.3 and Kv3.1 currents with an IC50 value of 3.7 and 32.7 microM, respectively. In addition, sibutramine reduced the tail current amplitude and slowed the deactivation of the tail currents of Kv1.3 and Kv3.1, resulting in a crossover phenomenon. These results indicate that sibutramine acts on Kv4.3, Kv1.3, and Kv3.1 as an open channel blocker.

Serotonin-induced ion channel modulations in mesenteric artery myocytes from normotensive and DOCA-salt hypertensive rats

Although serotonin (5-hydroxytryptamine, 5-HT) has been found to be a potent vasoconstrictor, a pivotal role of 5-HT in the control of appetite and mood control by the modulation of neuronal synapse has also been proposed. Selective 5-HT reuptake inhibitors (SSRIs) are frequently used to suppress appetite and treat depressive disorder, and the target protein of SSRIs is the 5-HT transporter (5-HTT) in the neuronal synapse. However, SSRIs may increase the free 5-HT concentration in circulating blood because platelets and vascular smooth muscles express functional 5-HTT. In addition, enhanced vasoactive action of 5-HT and alterations in 5-HT receptor subtypes have been reported in some types of hypertension. Therefore, we can infer that the use of drugs such as SSRIs in some hypertensive patients is potentially risky. Altered functional expression of ion channels in vascular smooth muscle is suggested to be a mechanism for the enhanced vasoconstriction by vasoactive agonists, including 5-HT. In this brief review, we compared the electrophysiological properties of mesenteric artery myocytes and their modulation by 5-HT between sham-operated control and deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

Serotonin depolarizes the membrane potential in rat mesenteric artery myocytes by decreasing voltage-gated K+ currents

We hypothesized that voltage-gated K+ (Kv) currents regulate the resting membrane potential (Em), and that serotonin (5-HT) causes Em depolarization by reducing Kv currents in rat mesenteric artery smooth muscle cells (MASMCs). The resting Em was about -40 mV in the nystatin-perforated patch configuration, and the inhibition of Kv currents by 4-aminopyridine caused marked Em depolarization. The inhibition of Ca2+-activated K+ (KCa) currents had no effect on Em. 5-HT (1 microM) depolarized Em by approximately 11 mV and reduced the Kv currents to approximately 63% of the control at -20 mV. Similar 5-HT effects were observed with the conventional whole-cell configuration with a weak Ca2+ buffer in the pipette solution, but not with a strong Ca2+ buffer. In the presence of tetraethylammonium (1mM), 5-HT caused Em depolarization similar to the control condition. These results indicate that the resting Em is largely under the regulation of Kv currents in rat MASMCs, and that 5-HT depolarizes Em by reducing Kv currents in a [Ca2+]i-dependent manner.

KChIP2b modulates the affinity and use-dependent block of Kv4.3 by nifedipine

Rapidly activating Kv4 voltage-gated ion channels are found in heart, brain, and diverse other tissues including colon and uterus. Kv4.3 can co-assemble with KChIP ancillary subunits, which modify kinetic behavior. We examined the affinity and use dependence of nifedipine block on Kv4.3 and its modulation by KChIP2b. Nifedipine (150 microM) reduced peak Kv4.3 current approximately 50%, but Kv4.3/KChIP2b current only approximately 27%. Nifedipine produced a very rapid component of open channel block in both Kv4.3 and Kv4.3/KChIP2b. However, recovery from the blocked/inactivated state was strongly sensitive to KChIP2b. Kv4.3 Thalf,recovery was slowed significantly by nifedipine (120.0+/-12.4 ms vs. 213.1+/-18.2 ms), whereas KChIP2b eliminated nifedipine's effect on recovery: Kv4.3/KChIP2b Thalf,recovery was 45.3+/-7.2 ms (control) and 47.8+/-8.2 ms (nifedipine). Consequently, Kv4.3 exhibited use-dependent nifedipine block in response to a series of depolarizing pulses which was abolished by KChIP2b. KChIPs alter drug affinity and use dependence of Kv4.3.

Phobic memory and somatic vulnerabilities in anorexia nervosa: a necessary unity?

Anorexia nervosa is a clinically significant illness that may be associated with permanent medical complications involving almost every organ system. The paper raises a question whether some of them are associated with premorbid vulnerability such as subcellular ion channel abnormalities ('channelopathy') that determines the clinical expression of the bodily response to self-imposed malnutrition. Aberrant channels emerge as a tempting, if rather speculative alternative to the notion of cognitively-driven neurotransmitter modulation deficit in anorexia nervosa. The concept of channelopathies is in keeping with some characteristics of anorexia nervosa, such as a genetically-based predisposition to hypophagia, early onset, cardiac abnormalities, an appetite-enhancing efficacy of some antiepileptic drugs, and others. The purpose of this article is to stimulate further basic research of ion channel biophysics in relation to restrictive anorexia.

Heteromultimeric Kv1 channels contribute to myogenic control of arterial diameter

Inhibition of vascular smooth muscle (VSM) delayed rectifier K+ channels (K(DR)) by 4-aminopyridine (4-AP; 200 micromol/L) or correolide (1 micromol/L), a selective inhibitor of Kv1 channels, enhanced myogenic contraction of rat mesenteric arteries (RMAs) in response to increases in intraluminal pressure. The molecular identity of K(DR) of RMA myocytes was characterized using RT-PCR, real-time PCR, and immunocytochemistry. Transcripts encoding the pore-forming Kvalpha subunits, Kv1.2, Kv1.4, Kv1.5, and Kv1.6, were identified and confirmed at the protein level with subunit-specific antibodies. Kvbeta transcript (beta1.1, beta1.2, beta1.3, and beta2.1) expression was also identified. Kv1.5 message was approximately 2-fold more abundant than that for Kv1.2 and Kv1.6. Transcripts encoding these three Kv1alpha subunits were approximately 2-fold more abundant in 1st/2nd order conduit compared with 4th order resistance RMAs, and Kvbeta1 was 8-fold higher than Kvbeta2 message. RMA K(DR) activated positive to -50 mV, exhibited incomplete inactivation, and were inhibited by 4-AP and correolide. However, neither alpha-dendrotoxin or kappa-dendrotoxin affected RMA K(DR), implicating the presence of Kv1.5 in all channels and the absence of Kv1.1, respectively. Currents mediated by channels because of coexpression of Kv1.2, Kv1.5, Kv1.6, and Kvbeta1.2 in human embryonic kidney 293 cells had biophysical and pharmacological properties similar to those of RMA K(DR). It is concluded that K(DR) channels composed of heteromultimers of Kv1 subunits play a critical role in myogenic control of arterial diameter.

A family exhibiting arterial tortuosity syndrome displays homozygosity for markers in the arterial tortuosity locus at chromosome 20q13

Arterial tortuosity associated with hyperextensible skin and hypermobility of joints, features that are characteristics of Ehlers-Danlos syndrome (EDS), has been described in several families. An arterial tortuosity locus has recently been mapped to chromosome 20q13. Here, we report a consanguineous Kurdish family in which an affected child manifested elongation and severe tortuosity of the aorta, carotid, and other arteries. Additional clinical symptoms include loose skin, hypermobile joints, hernias, and facial features that resemble EDS individuals. To examine whether the arterial tortuosity locus was involved in this child, homozygosity analysis was performed using microsatellite markers on 20q13. The affected child was found homozygous, whereas the unaffected parents and three siblings were heterozygous. Additional typing defined the genomic interval to a 37-cm region within which the arterial tortuosity locus is located. Three functional candidate genes (B4GALT5, KCNB1, and PTGIS) were sequenced. No mutations were discovered in the coding regions of these three genes and the promoter regions of B4GALT5 and KCNB1 genes. Moreover, the B4GALT5 mRNA expression was unaltered in patient-derived lymphoblastoid cells. In the PTGIS gene promoter, the affected child was homozygous for eight variable number of tandem repeats, while parents and unaffected siblings carried six repeats.

Non-contractile cells with thin processes resembling interstitial cells of Cajal found in the wall of guinea-pig mesenteric arteries

Arterial interstitial cells of Cajal (ICC)-like cells (AIL cells) with a multipolar, irregular, elongated shape and with numerous thin (often less than 1 microm), sometimes branching, processes with lengths up to approximately 60 microm were isolated enzymatically from 1st to 7th order branches of guinea-pig mesenteric artery. Some of the processes of AIL cells were growing (average speed approximately 0.15 microm min-1) and their growth was blocked by 10 microM latrunculin B, an inhibitor of actin polymerisation. Staining with BODIPY phalloidin, a fluorescent dye selective for F-actin, showed the presence of F-actin in the processes of AIL cells. Voltage clamp of single AIL cells revealed an inward current that was four times more dense than in myocytes and was abolished by 10 microM nicardipine, and an outward current carried exclusively by potassium ions that was reduced by 1 mM 4-aminopyridine and/or 100 nM iberiotoxin but unaffected by 10 nM dendrotoxin-K. Imaging of intracellular ionised calcium with fluo-4 using a laser scanning confocal microscope showed local or global calcium transients lasting several seconds in approximately 28 % of AIL cells. When membrane current was recorded simultaneously, the calcium transients were found to correspond to long-lasting transient outward currents, which occurred at potentials positive to -40 mV. Unlike myocytes, AIL cells did not contract in response to 1 mM caffeine or 5 microM noradrenaline, although they responded with a [Ca2+]i increase. The segments of intact arteries did not stain for c-kit, a marker of ICCs. Single AIL cells stained positive for vimentin, desmin and smooth muscle myosin. The presence of ICC-like cells is demonstrated for the first time in the media of resistance arteries.

Impaired voltage-gated K+ channel expression in brain during experimental cancer cachexia

Cancer-induced cachexia affects most advanced cancer patients. It is characterized by anorexia, profound metabolic dysfunctions, and severe neurological disorders. Here we show that voltage-gated potassium channel (Kv) expression is impaired in the brain of tumor-bearing animals. Expression of both delayed rectifier (Kv1.1, Kv1.2, Kv1.3, Kv1.5, Kv1.6, Kv2.1, Kv3.1, Kv4.2) and A-type potassium channels (Kv1.4, Kv3.3, Kv3.4) was greatly down-regulated in brain from animals bearing a Yoshida AH-130 ascites hepatoma. The possible compensatory mechanisms (Kv1.4/Kv4.2), expression of redundant genes (Kv3.1/Kv3.3) and heteromultimeric channel formation (Kv2.1/Kv9.3) were also affected. The high circulating levels of TNFalpha and the reduced expression of the anti-apoptotic protein Bcl-XL found in the brain of tumor-bearing animals indicate that this response could be mediated by an increase in brain cell death due to apoptosis. The results suggest that brain function is impaired during cancer cachexia, and may account for the cancer-induced anorectic response and other neurological alterations.

Different Kv2.1/Kv9.3 heteromer expression during brain and lung post-natal development in the rat

The Kv2.1/Kv9.3 heteromer generates an O2 sensitive potassium channel and induces a slow deactivation that has important consequences for brain and lung physiology. We examined the developmental regulation of Kv2.1 and Kv9.3 mRNAs in brain and lung. Both genes followed parallel expression patterns in brain, increasing progressively through post-natal life. In lung, however, the expression of the two genes followed opposite trends: Kv2.1 transcripts decreased, while Kv9.3 mRNA increased. The Kv9.3/Kv2.1 ratio shows that while in brain the expression of both genes followed a similar pattern, the relative abundance of Kv9.3 increased steadily through post-natal life in lung. Furthermore, there is selective regulation of gene expression during the suckling-weaning transition. Our results suggest that different Kv9.3/Kv2.1 ratios could have physiological implications in both organs during post-natal development, and that diet composition and selective tissue-specific insulin regulation modulate the expression of Kv2.1 and Kv9.3.