Coupling strength between localized Ca(2+) transients and K(+) channels is regulated by protein kinase C

Encapsulation of 4-oxo-N-(4-hydroxyphenyl) retinamide in human serum albumin nanoparticles promotes EZH2 degradation in preclinical neuroblastoma models

Neuroblastoma is the most prevalent and aggressive solid tumor that develops extracranially in children between the ages of 0-14 years, which accounts for 8-10% of all childhood malignancies and ∼15% of pediatric cancer-related mortality. The polycomb repressive complex 2 (PRC2) protein, EZH2, is overexpressed in neuroblastoma and mediates histone H3 methylation at lysine 27 (K27) positions through its methyl transferase activity and is a potential epigenetic silencer of many tumor suppressor genes in cancer. Phosphorylation of EZH2 decreases its stability and leads to proteasomal degradation. The 4-oxo-N-(4-hydroxyphenyl) retinamide (4O4HPR) promotes EZH2 degradation via activation of PKC-δ, but its limited solubility and physiological instability limit its application. In the current study, the encapsulation of 4O4HPR in Human Serum Albumin Nanoparticles (HSANPs) enhanced the solubility and physiological stability of the nanoformulation, leading to improved therapeutic efficacy through G2-M cell cycle arrest, depolarization of mitochondrial membrane potential, generation of reactive oxygen species and caspase 3 mediated apoptosis activation. The molecular mechanistic approach of 4O4HPR loaded HSANPs has activated caspase 3, which further cleaves PKC-δ into two fragments wherein the cleaved fragment of PKC-δ possesses the kinase activity that phosphorylates EZH2 and decreases the protein stability leading to its further ubiquitination in SH-SY5Y cells. Co-immunoprecipitation experiments revealed the direct interaction between PKC-δ and EZH2 phosphorylation, followed by ubiquitination. Moreover, 4O4HPR loaded HSANPs demonstrated improved in vivo biodistribution, greater dispersibility, and biocompatibility and exhibited enhanced protein instability and degradation of EZH2 in the neuroblastoma xenograft mouse model.

Methylation-reprogrammed CHRM3 results in vascular dysfunction in the human umbilical vein following IVF-ET

Assisted reproductive technology (ART) has been used globally among infertile couples. However, many epidemiological investigations have indicated that ART is associated with a range of long-term adverse health outcomes in offspring, including cardiovascular disease, obesity and increased plasma lipid levels. Until now, direct evidence has been limited regarding the pathological changes in vascular function in fetuses with ART. In this study, human umbilical cords were collected from healthy normal pregnancies and IVF-ET pregnancies. Vascular functional studies involving acetylcholine (ACh), antagonists of its specific receptors, and L-type calcium channel/PKC-MLC20 phosphorylation pathway specific inhibitors were conducted. Quantitative real-time PCR, Western blotting and methylation analyses were performed on umbilical vein samples. We found that the umbilical vein constriction induced by ACh in the IVF-ET group was significantly attenuated compared with that in the healthy normal pregnancy group, which was not only associated with the hypermethylation of ACh muscarinic receptor subtype 3 (CHRM3) and decreased expression of CHRM3, PKCβ and CaV1.2, but was also related to the reduced phosphorylation of MLC20. The present study revealed that the hypermethylation of CHRM3, leading to a reduction in CHRM3 expression and downregulation of the CaV1.2/PKC-MLC20 phosphorylation pathway, was responsible for the decreased sensitivity to ACh observed in the umbilical vein under IVF-ET conditions. The hypermethylation of CHRM3 caused by IVF-ET might play an important role in altered vasoconstriction and impact cardiovascular systems in the long run.

Goblet cell LRRC26 regulates BK channel activation and protects against colitis in mice

Goblet cells (GCs) are specialized cells of the intestinal epithelium contributing critically to mucosal homeostasis. One of the functions of GCs is to produce and secrete MUC2, the mucin that forms the scaffold of the intestinal mucus layer coating the epithelium and separates the luminal pathogens and commensal microbiota from the host tissues. Although a variety of ion channels and transporters are thought to impact on MUC2 secretion, the specific cellular mechanisms that regulate GC function remain incompletely understood. Previously, we demonstrated that leucine-rich repeat-containing protein 26 (LRRC26), a known regulatory subunit of the Ca²⁺-and voltage-activated K⁺ channel (BK channel), localizes specifically to secretory cells within the intestinal tract. Here, utilizing a mouse model in which MUC2 is fluorescently tagged, thereby allowing visualization of single GCs in intact colonic crypts, we show that murine colonic GCs have functional LRRC26-associated BK channels. In the absence of LRRC26, BK channels are present in GCs, but are not activated at physiological conditions. In contrast, all tested MUC2^- cells completely lacked BK channels. Moreover, LRRC26-associated BK channels underlie the BK channel contribution to the resting transepithelial current across mouse distal colonic mucosa. Genetic ablation of either LRRC26 or BK pore-forming α-subunit in mice results in a dramatically enhanced susceptibility to colitis induced by dextran sodium sulfate. These results demonstrate that normal potassium flux through LRRC26-associated BK channels in GCs has protective effects against colitis in mice.

Influence of protein corona and caveolae-mediated endocytosis on nanoparticle uptake and transcytosis

Transcytosis of nanoparticles (NPs) is emerging as an attractive alternative to the paracellular route in cancer drug delivery with studies suggesting targeting caveolae-mediated endocytosis to maximize NP transcytosis. However, there are limited studies on transcytosis of NPs, especially for corona-coated NPs. Most studies focused on cellular uptake as an indirect measure of the NP's transcellular permeability (Pd). Here, we probed the effect of protein corona on the uptake and transcytosis of 20, 40, 100, and 200 nm polystyrene nanoparticles (pNP-PC) across HUVECs in a microfluidic channel that modelled the microvasculature. We observed increased cell uptake with size of pNP-PC although it was the smallest 20 nm pNP-PC that exhibited the highest transcellular Pd. In the absence of corona however, cell uptake decreased with size, and the largest 200 nm pNP-PEG exhibited the lowest transcellular Pd. By inhibiting caveolae-mediated endocytosis in HUVECs, smaller pNPs had a larger drop in cell uptake than larger pNPs, regardless of surface coating. However, only the smallest (20 nm) and largest (200 nm) pNP-PC had a decrease in Pd following inhibition with MβCD. Our findings showed that the protein corona affected the transcytosis of NPs, and their uptake by caveolae-mediated endocytosis did not necessarily lead to transcytosis.

Molecular and functional characterization of inwardly rectifying K+ currents in murine proximal colon

KEY POINTS

Interstitial cells of Cajal (ICC) from murine colonic muscles express genes encoding inwardly rectifying K+ channels. Transcripts of Kcnj2 (Kir2.1), Kcnj4 (Kir2.3), Kcnj14 (Kir2.4), Kcnj5 (Kir3.4), Kcnj8 (Kir 6.1) and Kcnj11 (Kir6.2) were found in colonic ICC. A conductance with properties consistent with Kir2 channels was observed in ICC but not in smooth muscle cells (SMC). Despite expression of gene transcripts, G-protein gated K+ channel (Kir3) and KATP (Kir6) currents were not resolved in ICC. KATP is a conductance prominent in SMC. Kir2 antagonist caused depolarization of freshly dispersed ICC and colonic smooth muscles, suggesting that this conductance is active under resting conditions in colonic muscles. The conclusion of the present study is that ICC express the Ba2+ -sensitive, inwardly rectifying K+ conductance in colonic muscles. This conductance is most probably a result of heterotetramers of Kir2 gene products, with this regulating resting potentials and the excitability of colonic muscles.

ABSTRACT

Membrane potentials of gastrointestinal muscles are important because voltage-dependent Ca2+ channels in smooth muscle cells (SMC) provide the Ca2+ that triggers contraction. Regulation of membrane potential is complicated because SMC are electrically coupled to interstitial cells of Cajal (ICC) and PDGFRα+ cells. Activation of conductances in any of these cells affects the excitability of the syncytium. We explored the role of inward rectifier K+ conductances in colonic ICC that might contribute to regulation of membrane potential. ICC expressed Kcnj2 (Kir2.1), Kcnj4 (Kir2.3), Kcnj14 (Kir2.4), Kcnj5 (Kir3.4), Kcnj8 (Kir 6.1) and Kcnj11 (Kir6.2). Voltage clamp experiments showed activation of inward current when extracellular K+ ([K+ ]o ) was increased. The current was inwardly rectifying and inhibited by Ba2+ (10 μm) and ML-133 (10 μm). A similar current was not available in SMC. The current activated in ICC by elevated [K+ ]o was not affected by Tertiapin-Q. Gβγ, when dialysed into cells, failed to activate a unique, Tertiapin-Q-sensitive conductance. Freshly dispersed ICC showed no evidence of functional KATP . Pinacidil failed to activate current and the inward current activated by elevated [K+ ]o was insensitive to glibenclamide. Under current clamp, ML-133 caused the depolarization of isolated ICC and also that of cells impaled with microelectrodes in intact muscle strips. These findings show that ICC, when isolated freshly from colonic muscles, expressed a Ba2+ -sensitive, inwardly rectifying K+ conductance. This conductance is most probably a result of the expression of multiple Kir2 family paralogues, and the inwardly rectifying conductance contributes to the regulation of resting potentials and excitability of colonic muscles.

Dual-targeting biomimetic delivery for anti-glioma activity via remodeling the tumor microenvironment and directing macrophage-mediated immunotherapy

A dual-targeting biomimetic codelivery and treatment strategy was developed for anti-glioma activity.

Tumor-associated macrophages (TAMs) are the major components in the tumor microenvironment (TME). The polarization from the protumor M2 (TAM2) to antitumor M1 (TAM1) phenotype can not only lift the immunosuppressive constraints and elicit cytotoxic T-cell immunity but also augment the chemotherapy efficacy. However, the treatment feasibility by TAM modulation in brain tumors and the mechanisms remained unknown. A dual-targeting biomimetic codelivery and treatment strategy was developed for anti-glioma activity. We demonstrated that the albumin nanoparticles modified with dual ligands, a transferrin receptor (TfR)-binding peptide T12 and mannose, efficiently passed through the BBB via the nutrient transporters (i.e., TfR and the albumin-binding receptor SPARC) that were both overexpressed in the BBB and glioma cells, thus achieving biomimetic delivery to glioma. Importantly, after penetrating the BBB, this system can take advantage of the overexpression of the SPARC and mannose receptors on TAM2, thus also targeting the protumor TAM2. With the codelivery disulfiram/copper complex and regorafenib, the system efficiently inhibited the glioma cell proliferation and successfully “re-educated” the protumor TAM2 towards antitumor TAM1. The treatment efficacy was examined in the glioma-bearing nude mice and immunocompetent mice. It showed this system yielded an enhanced treatment outcome, owing to the synergistic combination of chemotherapy and macrophage-directed immunotherapy. The importance of this delivery and therapeutic strategy was to remodel the immune microenvironment and reprogram TAM and trigger macrophage-directed anti-glioma immunotherapy via the interplay of the TAM, Treg, and CD8⁺ T cells and the effector cytokines. The albumin-based biomimetic brain delivery also provides a promising method for the pharmacotherapy of brain diseases.

Transferrin-conjugated paclitaxel prodrugs for targeted cancer therapy

Paclitaxel (PTX) is one of the most effective chemotherapeutic drugs ever developed and is effective against a wide spectrum of tumors.

Serum Albumin Binding Inhibits Nuclear Uptake of Luminescent Metal-Complex-Based DNA Imaging Probes

The DNA binding and cellular localization properties of a new luminescent heterobimetallic Ir(III) Ru(II) tetrapyridophenazine complex are reported. Surprisingly, in standard cell media, in which its tetracationic, isostructural Ru(II) Ru(II) analogue is localized in the nucleus, the new tricationic complex is poorly taken up by live cells and demonstrates no nuclear staining. Consequent cell-free studies reveal that the Ir(III) Ru(II) complex binds bovine serum albumin, BSA, in Sudlow's Site I with a similar increase in emission and binding affinity to that observed with DNA. Contrastingly, in serum-free conditions the complex is rapidly internalized by live cells, where it localizes in cell nuclei and functions as a DNA imaging agent. The absence of serum proteins also greatly alters the cytotoxicity of the complex, where high levels of oncosis/necrosis are observed due to this enhanced uptake. This suggests that simply increasing the lipophilicity of a DNA imaging probe to enhance cellular uptake can be counterproductive as, due to increased binding to serum albumin protein, this strategy can actually disrupt nuclear targeting.

Maternal high-salt diets affected pressor responses and microvasoconstriction via PKC/BK channel signaling pathways in rat offspring

SCOPE

High-salt (HS) intake is linked to hypertension, and prenatal exposure to maternal HS diets may have long-term impact on cardiovascular systems. The relationship between HS diets and cardiovascular disease has received extensive attention. This study determined pressor responses and microvessel functions in the adult offspring rats exposed to prenatal HS.

METHODS AND RESULTS

The offspring of 5-month old as young adults in rats were used. Blood pressure, vascular tone, intracellular Ca(2+), and BK channels in mesenteric arteries were measured in the offspring. Phenylephrine (Phe)-induced pressor responses were significantly higher in the prenatal HS offspring. Vessel tension and intracellular Ca(2+) concentrations associated with Phe-induced pressor responses were increased in the mesenteric arteries of the HS offspring. PKC α- and δ-isoforms were upregulated in mesenteric arteries of the HS offspring. The enhanced Phe-mediated vascular activity was linked to the altered PKC-modulated BK channel functions.

CONCLUSION

The results suggested that prenatal exposure to HS altered microvascular activity probably via changes in PKC/BK signaling pathways, which may lead to increased risks of hypertension in the offspring.

Secondary structure of corona proteins determines the cell surface receptors used by nanoparticles

Nanoparticles used for biological and biomedical applications encounter a host of extracellular proteins. These proteins rapidly adsorb onto the nanoparticle surface, creating a protein corona. Poly(ethylene glycol) can reduce, but not eliminate, the nonspecific adsorption of proteins. As a result, the adsorbed proteins, rather than the nanoparticle itself, determine the cellular receptors used for binding, the internalization mechanism, the intracellular transport pathway, and the subsequent immune response. Using fluorescence microscopy and flow cytometry, we first characterize a set of polystyrene nanoparticles in which the same adsorbed protein, bovine serum albumin, leads to binding to two different cell surface receptors: native albumin receptors and scavenger receptors. Using a combination of circular dichroism spectroscopy, isothermal titration calorimetry, and fluorescence spectroscopy, we demonstrate that the secondary structure of the adsorbed bovine serum albumin protein controls the cellular receptors used by the protein-nanoparticle complexes. These results show that protein secondary structure is a key parameter in determining the cell surface receptor used by a protein-nanoparticle complex. We expect this link between protein structure and cellular outcomes will provide a molecular basis for the design of nanoparticles for use in biological and biomedical applications.

Rare Earth Nanoprobes for Functional Biomolecular Imaging and Theranostics

Contrast agents designed to visualize the molecular mechanisms underlying cancer pathogenesis and progression have deepened our understanding of disease complexity and accelerated the development of enhanced drug strategies targeted to specific biochemical pathways. For the next generation probes and imaging systems to be viable, they must exhibit enhanced sensitivity and robust quantitation of morphologic and contrast features, while offering the ability to resolve the disease-specific molecular signatures that may be critical to reconstitute a more comprehensive portrait of pathobiology. This feature article provides an overview on the design and advancements of emerging biomedical optical probes in general and evaluates the promise of rare earth nanoprobes, in particular, for molecular imaging and theranostics. Combined with new breakthroughs in nanoscale probe configurations, and improved dopant compositions, and multimodal infrared optical imaging, rare-earth nanoprobes can be used to address a wide variety of biomedical challenges, including deep tissue imaging, real-time drug delivery tracking and multispectral molecular profiling.

Spontaneous and evoked contractions are regulated by PKC-mediated signaling in detrusor smooth muscle: involvement of BK channels

Protein kinase C (PKC) and large conductance Ca(2+)-activated potassium channels (BK) are downregulated in the detrusor smooth muscle (DSM) in partial bladder outlet obstruction (PBOO). DSM from these bladders display increased spontaneous activity. This study examines the involvement of PKC in the regulation of spontaneous and evoked DSM contractions and whether pharmacologic inhibition of PKC in normal DSM contributes to increased detrusor excitability. Results indicate the PKC inhibitor bisindolylmaleimide 1 (Bim-1) prevented a decline in the amplitude of spontaneous DSM contractions over time in vitro, and these contractions persist in the presence of tetrodotoxin. Bim-1 also reduced the basal DSM tone, and the ability to maintain force in response to electrical field stimulation, but did not affect maximum contraction. The PKC activator phorbol-12,13-dibutyrate (PDBu) significantly reduced the amplitude and increased the frequency of spontaneous contractions at low concentrations (10 nM), while causing an increase in force at higher concentrations (1 μM). Preincubation of DSM strips with iberiotoxin prevented the inhibition of spontaneous contractions by PDBu. The BK channel openers isopimaric acid and NS1619 reduced the Bim-1-induced enhancement of spontaneous contractions in DSM strips. Our data suggest that PKC has a biphasic activation profile in the DSM and that it may play an important role in maintaining the quiescent state of the normal bladder during storage through the effects on BK channel, while helping to maintain force required for bladder emptying. The data also suggest that PKC dysfunction, as seen in PBOO, contributes to detrusor overactivity.

Baicalin, a flavonoid from Scutellaria baicalensis Georgi, activates large-conductance Ca2+-activated K+ channels via cyclic nucleotide-dependent protein kinases in mesenteric artery

Baicalin isolated from Scutellaria baicalensis is a traditional Chinese herbal medicine used for cardiovascular dysfunction. The ionic mechanism of the vasorelaxant effects of baicalin remains unclear. We investigated whether baicalin relaxes mesenteric arteries (MAs) via large-conductance Ca2+-activated K+ (BK(Ca)) channel activation and voltage-dependent Ca2+ channel (VDCC) inhibition. The contractility of MA was determined by dual wire myograph. BK(Ca) channels and VDCCs were measured using whole-cell recordings in single myocytes, enzymatically dispersed from rat MAs. Baicalin (10-100 microM) attenuated 80 mM KCl-contracted MA in a concentration-related manner. L-NAME (30 microM) and indomethacin (10 microM) little affected baicalin (100 microM)-induced vasorelaxations. Contractions induced by iberiotoxin (IbTX, 0.1 microM), Bay K8644 (0.1 microM) or PMA (10 microM) were abolished by baicalin 100 microM. In MA myocytes, baicalin (0.3-30 microM) enhanced BK(Ca) channel activity in a concentration-dependent manner. Increased BK(Ca) currents were abolished by IbTX (0.1 microM). Baicalin-mediated (30 microM) BK(Ca) current activation was significantly attenuated by an adenylate cyclase inhibitor (SQ 22536, 10 microM), a soluble guanylate cyclase inhibitor (ODQ, 10 microM), competitive antagonists of cAMP and cGMP (Rp-cAMP, 100 microM and Rp-cGMP, 100 microM), and cAMP- and cGMP-dependent protein kinase inhibitors (KT5720, 0.3 microM and KT5823, 0.3 microM). Perfusate with PMA (0.1 microM) abolished baicalin-enhanced BK(Ca) currents. Additionally, baicalin (0.3-30 microM) reduced the amplitude of VDCC currents in a concentration-dependent manner and abolished VDCC activator Bay K8644-enhanced (0.1 microM) currents. Baicalin produced MA relaxation by activating BK(Ca) and inhibiting VDCC channels by endothelium-independent mechanisms and by stimulating the cGMP/PKG and cAMP/PKA pathways.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

CaM kinase II in colonic smooth muscle contributes to dysmotility in murine DSS-colitis

BACKGROUND

Altered calcium mobilization has been implicated in the development of colonic dysmotility in inflammatory bowel disease. The aim of this study was to investigate the mechanisms by which disrupted intracellular Ca(2+) signalling contributes to the impaired contractility of colon circular smooth muscles.

METHODS

Acute colitis was induced in C57Bl/6 mice with dextran sulphate sodium (DSS) in the drinking water for 5 days.

KEY RESULTS

Spontaneous and acetylcholine-evoked contractions, caffeine-evoked hyperpolarization, and SERCA2 and phospholamban expression were reduced compared with controls. Tetrodotoxin did not restore control levels of contractile activity. The amplitudes, but not the frequency, of intracellular Ca(2+) waves were increased compared with controls. Caffeine abolished intracellular Ca(2+) waves in control smooth muscle cells, but not in smooth muscle cells from DSS-treated mice. CaM kinase II activity and cytosolic levels of HDAC4 were increased, and I kappaB alpha levels were decreased in distal colon smooth muscles from DSS-treated mice.

CONCLUSIONS & INFERENCES

These results suggest that disruptions in intracellular Ca(2+) mobilization due to down-regulation of SERCA2 and phospholamban expression lead to increased CaM kinase II activity and cytosolic HDAC4 that may contribute to the dysmotility of colonic smooth muscles in colitis by enhancing NF-kappaB activity.

Intercellular adhesion molecule-1-dependent neutrophil adhesion to endothelial cells induces caveolae-mediated pulmonary vascular hyperpermeability

We investigated the role of caveolae in the mechanism of increased pulmonary vascular permeability and edema formation induced by the activation of polymorphonuclear neutrophils (PMNs). We observed that the increase in lung vascular permeability induced by the activation of PMNs required caveolin-1, the caveolae scaffold protein. The permeability increase induced by PMN activation was blocked in caveolin-1 knockout mice and by suppressing caveolin-1 expression in rats. The response was also dependent on Src phosphorylation of caveolin-1 known to activate caveolae-mediated endocytosis in endothelial cells. To address the role of PMN interaction with endothelial cells, we used an intercellular adhesion molecule (ICAM)-1 blocking monoclonal antibody. Preventing the ICAM-1-mediated PMN binding to endothelial cells abrogated Src phosphorylation of caveolin-1, as well as the increase in endothelial permeability. Direct ICAM-1 activation by crosslinking recapitulated these responses, suggesting that ICAM-1 activates caveolin-1 signaling responsible for caveolae-mediated endothelial hyperpermeability. Our results provide support for the novel concept that a large component of pulmonary vascular hyperpermeability induced by activation of PMNs adherent to the vessel wall is dependent on signaling via caveolin-1 and increased caveolae-mediated transcytosis. Thus, it is important to consider the role of the transendothelial vesicular permeability pathway that contributes to edema formation in developing therapeutic interventions against PMN-mediated inflammatory diseases such as acute lung injury.

Activation of BKCa channels via cyclic AMP- and cyclic GMP-dependent protein kinases by eugenosedin-A in rat basilar artery myocytes

BACKGROUND AND PURPOSE

The study investigated whether eugenosedin-A, a 5-hydroxytryptamine and alpha/beta adrenoceptor antagonist, enhanced delayed-rectifier potassium (K(DR))- or large-conductance Ca(2+)-activated potassium (BK(Ca))-channel activity in basilar artery myocytes through cyclic AMP/GMP-dependent and -independent protein kinases.

EXPERIMENTAL APPROACH

Cerebral smooth muscle cells (SMCs) were enzymatically dissociated from rat basilar arteries. Conventional whole cell, perforated and inside-out patch-clamp electrophysiology was used to monitor K(+)- and Ca(2+)-channel activities.

KEY RESULTS

Eugenosedin-A (1 microM) did not affect the K(DR) current but dramatically augmented BK(Ca) channel activity in a concentration-dependent manner. Increased BK(Ca) current was abolished by charybdotoxin (ChTX, 0.1 microM) or iberiotoxin (IbTX, 0.1 microM), but not affected by a small-conductance K(Ca) blocker (apamin, 100 microM). BK(Ca) current activation by eugenosedin-A was significantly inhibited by an adenylate cyclase inhibitor (SQ 22536, 10 microM), a soluble guanylate cyclase inhibitor (ODQ, 10 microM), competitive antagonists of cAMP and cGMP (Rp-cAMP, 100 microM and Rp-cGMP, 100 microM), and cAMP- and cGMP-dependent protein kinase inhibitors (KT5720, 0.3 microM and KT5823, 0.3 microM). Eugenosedin-A reversed the inhibition of BK(Ca) current induced by the protein kinase C activator, phorbol myristyl acetate (PMA, 0.1 microM). Eugenosedin-A also prevented BK(Ca) current inhibition induced by adding PMA, KT5720 and KT5823. Moreover, eugenosedin-A reduced the amplitude of voltage-dependent L-type Ca(2+) current (I(Ca,L)), but without modifying the voltage-dependence of the current.

CONCLUSIONS AND IMPLICATIONS

Eugenosedin-A enhanced BK(Ca) currents by stimulating the activity of cyclic nucleotide-dependent protein kinases. Physiologically, this activation would result in the closure of voltage-dependent calcium channels and thereby relax cerebral SMCs.

Activation of NFATc3 down-regulates the beta1 subunit of large conductance, calcium-activated K+ channels in arterial smooth muscle and contributes to hypertension

Large conductance, Ca2+-activated K+ (BK) channels modulate the excitability and contractile state of arterial smooth muscle. Recently, we demonstrated that during hypertension, expression of the accessory beta1 subunit was decreased relative to the pore-forming alpha subunit of the BK channel. Reduced beta1 subunit expression resulted in BK channels with impaired function due to lowered sensitivity to Ca2+. Here, we tested the hypothesis that activation of the calcineurin/NFATc3 signaling pathway down-regulates beta1 expression during angiotensin II-induced hypertension. Consistent with this hypothesis, we found that in vivo administration of angiotensin II-activated calcineurin/NFATc3 signaling in arterial smooth muscle. During angiotensin II infusion, arterial smooth muscle BK channel function was decreased in wild type (WT) but not in NFATc3 null (NFATc3-/-) mice. Accordingly, beta1 expression was decreased in WT but not in NFATc3-/- arteries. Angiotensin II-induced down-regulation of the beta1 subunit required Ca2+ influx via L-type Ca2+ channels. However, in the absence of angiotensin II, moderate elevation of [Ca2+]i alone was not sufficient to activate NFAT transcriptional activity and, thus, decrease beta1 subunit expression. Importantly, angiotensin II infusion increased systemic blood pressure to a lower extent in NFATc3-/- than in WT mice, indicating that this transcription factor is required for the development of severe hypertension during chronic angiotensin II signaling activation. We conclude that activation of calcineurin and NFATc3 during sustained angiotensin II signaling down-regulates the expression of the beta1 subunit of the BK channel, which in turn contributes to arterial dysfunction and the development of hypertension.

KCa channel insensitivity to Ca2+ sparks underlies fractional uncoupling in newborn cerebral artery smooth muscle cells

In smooth muscle cells, localized intracellular Ca2+ transients, termed "Ca2+ sparks," activate several large-conductance Ca2+-activated K+ (KCa) channels, resulting in a transient KCa current. In some smooth muscle cell types, a significant proportion of Ca2+ sparks do not activate KCa channels. The goal of this study was to explore mechanisms that underlie fractional Ca2+ spark-KCa channel coupling. We investigated whether membrane depolarization or ryanodine-sensitive Ca2+ release (RyR) channel activation modulates coupling in newborn (1- to 3-day-old) porcine cerebral artery myocytes. At steady membrane potentials of -40, 0, and +40 mV, mean transient KCa current frequency was approximately 0.18, 0.43, and 0.26 Hz and KCa channel activity [number of KCa channels activated by Ca2+ sparksxopen probability of KCa channels at peak of Ca2+ sparks (NPo)] at the transient KCa current peak was approximately 4, 12, and 24, respectively. Depolarization between -40 and +40 mV increased KCa channel sensitivity to Ca2+ sparks and elevated the percentage of Ca2+ sparks that activated a transient KCa current from 59 to 86%. In a Ca2+-free bath solution or in diltiazem, a voltage-dependent Ca2+ channel blocker, steady membrane depolarization between -40 and +40 mV increased transient KCa current frequency up to approximately 1.6-fold. In contrast, caffeine (10 microM), an RyR channel activator, increased mean transient KCa current frequency but did not alter Ca2+ spark-KCa channel coupling. These data indicate that coupling is increased by mechanisms that elevate KCa channel sensitivity to Ca2+ sparks, but not by RyR channel activation. Overall, KCa channel insensitivity to Ca2+ sparks is a prominent factor underlying fractional Ca2+ spark uncoupling in newborn cerebral artery myocytes.

VIP and PACAP regulate localized Ca2+ transients via cAMP-dependent mechanism

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been suggested as participants in enteric inhibitory neural regulation of gastrointestinal motility. These peptides cause a variety of postjunctional responses including membrane hyperpolarization and inhibition of contraction. Neuropeptides released from enteric motor neurons can elicit responses by direct stimulation of smooth muscle cells as opposed to other transmitters that rely on synapses between motor nerve terminals and interstitial cells of Cajal. Therefore, we studied the responses of murine colonic smooth muscle cells to VIP and PACAP(1-38) with confocal microscopy and patch-clamp technique. Localized Ca2+ transients (Ca2+ puffs) were observed in colonic myocytes, and these events coupled to spontaneous transient outward currents (STOCs). VIP and PACAP increased Ca2+ transients and STOC frequency and amplitude. Application of dibutyryl cAMP had similar effects. The adenylyl cyclase blocker MDL-12,330A alone did not affect spontaneous Ca2+ puffs and STOCs but prevented responses to VIP. Disruption of A-kinase-anchoring protein (AKAP) associations by application of AKAP St-Ht31 inhibitory peptide had effects similar to those of MDL-12,330A. Inhibition of ryanodine receptor channels did not block spontaneous Ca2+ puffs and STOCs but prevented the effects of dibutyryl cAMP. These findings suggest that regulation of Ca2+ transients (which couple to activation of STOCs) may contribute to the inhibitory effects of VIP and PACAP. Regulation of Ca2+ transients by VIP and PACAP occurs via adenylyl cyclase, increased synthesis of cAMP, and PKA-dependent regulation of ryanodine receptor channels.

Transport across the endothelium: regulation of endothelial permeability

An important function of the endothelium is to regulate the transport of liquid and solutes across the semi-permeable vascular endothelial barrier. Two cellular pathways controlling endothelial barrier function have been identified. The transcellular pathway transports plasma proteins of the size of albumin or greater via the process of transcytosis in vesicle carriers originating from cell surface caveolae. Specific signalling cues are able to induce the internalisation of caveolae and their movement to the basal side of the endothelium. Caveolin-1, the primary structural protein required for the formation of caveolae, is also important in regulating vesicle trafficking through the cell by controlling the activity and localisation of signalling molecules that mediate vesicle fission, endocytosis, fusion and finally exocytosis. An important function of the transcytotic pathways is to regulate the delivery of albumin and immunoglobulins, thereby controlling tissue oncotic pressure and host-defence. The paracellular pathway induced during inflammation is formed by gaps between endothelial cells at the level of adherens and tight junctional complexes. Paracellular permeability is increased by second messenger signalling pathways involving Ca2+ influx via activation of store-operated channels, protein kinase Calpha (PKCalpha), and Rho kinase that together participate in the stimulation of myosin light chain phosphorylation, actin-myosin contraction, and disruption of the junctions. In this review of the field, we discuss the current understanding of the signalling pathways regulating paracellular and transcellular endothelial permeability.

Gating and ionic currents reveal how the BKCa channel's Ca2+ sensitivity is enhanced by its beta1 subunit

Large-conductance Ca(2+)-activated K(+) channels (BK(Ca) channels) are regulated by the tissue-specific expression of auxiliary beta subunits. Beta1 is predominantly expressed in smooth muscle, where it greatly enhances the BK(Ca) channel's Ca(2+) sensitivity, an effect that is required for proper regulation of smooth muscle tone. Here, using gating current recordings, macroscopic ionic current recordings, and unitary ionic current recordings at very low open probabilities, we have investigated the mechanism that underlies this effect. Our results may be summarized as follows. The beta1 subunit has little or no effect on the equilibrium constant of the conformational change by which the BK(Ca) channel opens, and it does not affect the gating charge on the channel's voltage sensors, but it does stabilize voltage sensor activation, both when the channel is open and when it is closed, such that voltage sensor activation occurs at more negative voltages with beta1 present. Furthermore, beta1 stabilizes the active voltage sensor more when the channel is closed than when it is open, and this reduces the factor D by which voltage sensor activation promotes opening by approximately 24% (16.8-->12.8). The effects of beta1 on voltage sensing enhance the BK(Ca) channel's Ca(2+) sensitivity by decreasing at most voltages the work that Ca(2+) binding must do to open the channel. In addition, however, in order to fully account for the increase in efficacy and apparent Ca(2+) affinity brought about by beta1 at negative voltages, our studies suggest that beta1 also decreases the true Ca(2+) affinity of the closed channel, increasing its Ca(2+) dissociation constant from approximately 3.7 microM to between 4.7 and 7.1 microM, depending on how many binding sites are affected.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Ion channels in mesangial cells: function, malfunction, or fiction

Ion channels in glomerular mesangial cells from humans, rats, and mice have been studied by electrophysiological, molecular, and gene-knockout methods. Two channels, a large, Ca(2+)-activated K(+) channel (BK) and a store-operated Ca(2+) channel (SOCC), can be defined with respect to molecular structure and function. Human BK, comprised of a pore-forming alpha-subunit and an accessory beta1-subunit, operate as Ca(2+)-sensing feedback modulators of contractile tone. SOCC have also been characterized in a mouse cell line; they are comprised of molecules belonging to the transient receptor potential subfamily.

Neuronal correlates of gastric pain induced by fundus distension: a 3T-fMRI study

Visceral hypersensitivity in gastric fundus is a possible pathogenesis for functional dyspepsia. The cortical representation of gastric fundus is still unclear. Growing evidence shows that the insula, but not the primary or secondary somatosensory region (SI or SII), may be the cortical target for visceral pain. Animal studies have also demonstrated that amygdala plays an important role in processing visceral pain. We used fMRI to study central projection of stomach pain from fundus balloon distension. We also tested the hypothesis that there will be neither S1 nor S2 activation, but amygdala activation with the fundus distension. A 3T-fMRI was performed on 10 healthy subjects during baseline, fullness (12.7 +/- 0.6 mmHg) and moderate gastric pain (17.0 +/- 0.8 mmHg). fMRI signal was modelled by convolving the predetermined psychophysical response. Statistical comparisons were performed between conditions on a group level. Gastric pain activated a wide range of cortical and subcortical structures, including thalamus and insula, anterior and posterior cingulate cortices, basal ganglia, caudate nuclei, amygdala, brain stem, cerebellum and prefrontal cortex (P < 0.001). A subset of these neuronal substrates was engaged in the central processing of fullness sensation. SI and SII were not activated during the fundus stimulation. In conclusion, the constellation of neuronal structures activated by fundus distension overlaps the pain matrices induced musculocutaneous pain, with the exception of the absence of SI or SII activation. This may account for the vague nature of visceral sensation/pain. Our data also confirms that the insula and amygdala may act as the central role in visceral sensation/pain, as well as in the proposed sensory-limbic model of learning and memory of pain.

Albumin mediates the transcytosis of myeloperoxidase by means of caveolae in endothelial cells

Myeloperoxidase (MPO), the phagocyte hemoprotein involved in neutrophil host defense and consuming nitric oxide (*NO), induces the nitration of extracellular matrix proteins and tissue remodeling subsequent to its transcytosis across the endothelial barrier. We addressed the role of an interaction of MPO with albumin as a requirement for MPO transport across the endothelium. Matrix-assisted laser desorption/ionization MS analysis of 80- and 60-kDa proteins purified from human lung tissue [with a human serum albumin (HSA)-affinity column] identified these albumin-binding proteins as MPO and MPO-heavy chain. A peptide corresponding to the MPO-heavy chain residues 425-454 demonstrated high-affinity binding to HSA. Replacement of the positively charged residues, R and K with G, prevented the binding of HSA to the peptide. We observed that albumin increased the binding of (125)I-MPO to lung microvascular endothelial cells by 2-fold and the rate of transendothelial flux of (125)I-MPO in cultured monolayers and intact vessels. Disruption of caveolae with cyclodextrin prevented the albumin-induced increase in transendothelial flux of (125)I-MPO. We also observed by confocal imaging that albumin induced the rapid internalization of MPO and its colocalization with albumin-labeled vesicles. MPO colocalized with the caveolae markers cholera toxin subunit B and caveolin 1 in the endocytosed vesicles. Thus, transcytosis of MPO by caveolae induced by its charge-dependent interaction with albumin is an important means of delivering MPO to the subendothelial space. Albumin-mediated transport of MPO may thereby regulate NO bioavailability and formation of NO-derived oxidants in the vessel wall.

Role of Src-induced Dynamin-2 Phosphorylation in Caveolae-mediated Endocytosis in Endothelial Cells

Albumin transcytosis, a determinant of transendothelial permeability, is mediated by the release of caveolae from the plasma membrane. We addressed the role of Src phosphorylation of the GTPase dynamin-2 in the mechanism of caveolae release and albumin transport. Studies were made in microvascular endothelial cells in which the uptake of cholera toxin subunit B, a marker of caveolae, and (125)I-albumin was used to assess caveolae-mediated endocytosis. Albumin binding to the 60-kDa cell surface albumin-binding protein, gp60, induced Src activation (phosphorylation on Tyr(416)) within 1 min and resulted in Src-dependent tyrosine phosphorylation of dynamin-2, which increased its association with caveolin-1, the caveolae scaffold protein. Expression of kinase-defective Src mutant interfered with the association between dynamin-2, which caveolin-1 and prevented the uptake of albumin. Expression of non-Src-phosphorylatable dynamin (Y231F/Y597F) resulted in reduced association with caveolin-1, and in contrast to WT-dynamin-2, the mutant failed to translocate to the caveolin-rich membrane fraction. The Y231F/Y597F dynamin-2 mutant expression also resulted in impaired albumin and cholera toxin subunit B uptake and reduced transendothelial albumin transport. Thus, Src-mediated phosphorylation of dynamin-2 is an essential requirement for scission of caveolae and the resultant transendothelial transport of albumin.

Localised calcium release events in cells from the muscle of guinea-pig gastric fundus

After enzymatic dispersion of the muscle of the guinea-pig gastric fundus, single elongated cells were observed which differed from archetypal smooth muscle cells due to their knurled, tuberose or otherwise irregular surface morphology. These, but not archetypal smooth muscle cells, consistently displayed spontaneous localized (i.e. non-propagating) intracellular calcium ([Ca(2+)](i)) release events. Such calcium events were novel in their magnitude and kinetic profiles. They included short transient events, plateau events and events which coalesced spatially or temporally (compound events). Quantitative analysis of the events with an automatic detection programme showed that their spatio-temporal characteristics (full width and full duration at half-maximum amplitude) were approximately exponentially distributed. Their amplitude distribution suggested the presence of two release modes. Carbachol application caused an initial cell-wide calcium transient followed by an increase in localized calcium release events. Pharmacological analysis suggested that localized calcium release was largely dependent on external calcium entry acting on both inositol trisphosphate receptors (IP(3)Rs) and ryanodine receptors (RyRs) to release stored calcium. Nominally calcium-free external solution immediately and reversibly abolished all localized calcium release without blocking the initial transient calcium release response to carbachol. This was inhibited by 2-APB (100 microm), ryanodine (10 or 50 microm) or U-73122 (1 microm). 2-APB (100 microm), xestospongin C (XeC, 10 microm) or U-73122 (1 microm) blocked both spontaneous localized calcium release and localized release stimulated by 10 microm carbachol. Ryanodine (50 microm) also inhibited spontaneous release, but enhanced localized release in response to carbachol. This study represents the first characterization of localized calcium release events in cells from the gastric fundus.

Beta 1-subunits are required for regulation of coupling between Ca2+ transients and Ca2+-activated K+ (BK) channels by protein kinase C

Colonic myocytes have spontaneous, localized, Ins (1,4,5) trisphosphate (IP3) receptor-dependent Ca2+ transients that couple to the activation of Ca2+-dependent K+ channels and spontaneous transient outward currents (STOCs). We previously reported that the coupling strength between spontaneous Ca2+ transients and large conductance Ca2+ activated K+ (BK) channels is regulated by Ca2+ influx through nonselective cation channels and activation of protein kinase C (PKC). Here, we used confocal microscopy and the patch-clamp technique to further investigate the coupling between localized Ca2+ transients and STOCs in colonic myocytes from animals lacking the regulatory beta1-subunit of BK channels. Myocytes from beta1-knockout (beta1-/-) animals loaded with fluo 4 showed typical localized Ca2+ transients, but the STOCs coupled to these events were of abnormally low amplitude. Reduction in external Ca2+ or application of inhibitors of nonselective cation channels (SKF-96365) caused no significant change in the amplitude or frequency of STOCs. Likewise, an inhibitor of PKC, GF 109203X, had no significant effect on STOCs. Single-channel recording from BK channels showed that application of an activator (PMA) and an inhibitor (GF 109203X) of PKC did not affect BK channel openings in myocytes of beta1-/- mice. These data show that PKC-dependent regulation of coupling strength between Ca2+ transients and STOCs in colonic myocytes depends upon the interaction between alpha- and beta1-subunits.

Neuroscience. Feeling the pain of social loss

Poets have long waxed lyrical about the pain of a broken heart. Now, as Panksepp explains in his Perspective, this metaphor may reflect real events in the mammalian brain. A new brain neuroimaging study (Eisenberger et al.) reveals that the brain areas that are activated during the distress caused by social exclusion are also those activated during physical pain. Thus, we now have an explanation for the feeling of physical pain that accompanies emotional loss-whether that be the loss of a loved one, rejection by one's social group, or the distress of separation experienced by young animals.

Substance P modulates localized calcium transients and membrane current responses in murine colonic myocytes

1. Neurokinins contribute to the neural regulation of gastrointestinal (GI) smooth muscles. We studied responses of murine colonic smooth muscle cells to substance P (SP) and NK(1) and NK(2) agonists using confocal microscopy and the patch clamp technique. 2. Colonic myocytes generated localized Ca(2+) transients that were coupled to spontaneous transient outward currents (STOCs). SP (10(-10) M) increased Ca(2+) transients and STOCs. Higher concentrations of SP (10(-6) M) increased basal Ca(2+) and inhibited Ca(2+) transients and STOCs. 3. Effects of SP were due to increased Ca(2+) entry via L-type Ca(2+) channels, and were mediated by protein kinase C (PKC). Nifedipine (10(-6) M) and the PKC inhibitor, GF 109203X (10(-6) M) reduced L-type Ca(2+) current and blocked the effects of SP. 4. SP responses depended upon parallel stimulation of NK(1) and NK(2) receptors. NK(1) agonist ([Sar(9),Met(O(2))(11)]-substance P; SSP) and NK(2) agonists (neurokinin A (NKA) or GR-64349) did not mimic the effects of SP alone, but NK(1) and NK(2) agonists were effective when added in combination (10(-10)-10(-6) M). Consistent with this, either an NK(1)-specific antagonist (GR-82334; 10(-7) M) or an NK(2)-specific antagonist (MEN 10,627; 10(-7) M) blocked responses to SP (10(-6) M). 5. Ryanodine (10(-5) M) blocked the increase in Ca(2+) transients and STOCs in response to SP (10(-10) M). 6. Our findings show that low concentrations of SP, via PKC-dependent enhancement of L-type Ca(2+) current and recruitment of ryanodine receptors, stimulate Ca(2+) transients. At higher concentrations of SP (10(-6) M), basal Ca(2+) increases and spontaneous Ca(2+) transients and STOCs are inhibited.

Sarcoplasmic reticulum calcium load regulates rat arterial smooth muscle calcium sparks and transient K(Ca) currents

The regulation of calcium (Ca(2+)) sparks and transient calcium-sensitive K(+) (K(Ca)) currents by acute changes in sarcoplasmic reticulum (SR) Ca(2+) load ([Ca(2+)](SR)) was investigated in rat cerebral artery smooth muscle cells using laser-scanning confocal microscopy in combination with patch clamp electrophysiology. [Ca(2+)](SR) was elevated by: (i) increasing the activity of the SR Ca(2+)-ATPase with an anti-phospholamban monoclonal antibody, or (ii) blocking Ca(2+) release from the SR with tetracaine, a membrane-permeant, reversible ryanodine-sensitive Ca(2+) release (RyR) channel blocker. Alternatively, [Ca(2+)](SR) was progressively decreased over time with a low concentration of thapsigargin (20 nM), a SR Ca(2+)-ATPase blocker. An elevation in [Ca(2+)](SR) increased Ca(2+) spark and transient K(Ca) current frequency, but did not alter the amplitude, decay or spatial spread of Ca(2+) sparks or the coupling ratio or amplitude correlation between Ca(2+) sparks and evoked transient K(Ca) currents. Decreasing [Ca(2+)](SR) reduced Ca(2+) spark frequency, amplitude and spatial spread and this reduced transient K(Ca) current frequency and amplitude. However, even when mean Ca(2+) spark amplitude and spread decreased by up to 47 and 56 % of control, respectively, the coupling ratio or amplitude correlation between Ca(2+) sparks and transient K(Ca) currents was not affected. These data demonstrate that acute changes in [Ca(2+)](SR) regulate Ca(2+) sparks and transient K(Ca) currents in arterial smooth muscle cells.