KCa3.1-Dependent Hyperpolarization Enhances Intracellular Ca2+ Signaling Induced by fMLF in Differentiated U937 Cells

Effects of exposure to alternating low-intensity, intermediate-frequency electric fields on the differentiation of human leukemic cell line U937

Studying the bioeffects of electric fields have been the subject of ongoing research which led to promising therapeutic effect, particularly in cancer treatment. Here, we investigated the impact of low-intensity, intermediate-frequency alternating electric fields on the differentiation of human myeloid leukemia cell line U937. The results showed a near twofold increase in differentiation of U937 cells treated for 24 h by alternating 600 kHz, 150 V/m electric fields, in comparison to their control groups. This measure was evaluated by latex bead phagocytosis assay, nitro blue tetrazolium test, and cell cycle analysis which revealed a significant shift in the number of cells from G2 +M to G0 +G1 phases. The simulation result for the intracellular field intensity showed around 50% attenuation with respect to the applied external field for our setup which ruled out masking of the applied field by the internal electric noise of the cell. Based on previous studies we postulate a possible calcium-related effect for the observed differentiation, yet the exact underlying mechanism requires further investigation. Finally, our results may offer a potential therapeutic method for leukemia in the future.

Progress on role of ion channels of cardiac fibroblasts in fibrosis

Cardiac fibrosis is defined as excessive deposition of extracellular matrix (ECM) in pathological conditions. Cardiac fibroblasts (CFs) activated by injury or inflammation differentiate into myofibroblasts (MFs) with secretory and contractile functions. In the fibrotic heart, MFs produce ECM which is composed mainly of collagen and is initially involved in maintaining tissue integrity. However, persistent fibrosis disrupts the coordination of excitatory contractile coupling, leading to systolic and diastolic dysfunction, and ultimately heart failure. Numerous studies have demonstrated that both voltage- and non-voltage-gated ion channels alter intracellular ion levels and cellular activity, contributing to myofibroblast proliferation, contraction, and secretory function. However, an effective treatment strategy for myocardial fibrosis has not been established. Therefore, this review describes the progress made in research related to transient receptor potential (TRP) channels, Piezo1, Ca²⁺ release-activated Ca²⁺ (CRAC) channels, voltage-gated Ca²⁺ channels (VGCCs), sodium channels, and potassium channels in myocardial fibroblasts with the aim of providing new ideas for treating myocardial fibrosis.

Inhibition of KCa3.1 Channels Suppresses Atrial Fibrillation via the Attenuation of Macrophage Pro-inflammatory Polarization in a Canine Model With Prolonged Rapid Atrial Pacing

Aims: To investigate the role of KCa3. 1 inhibition in macrophage pro-inflammatory polarization and vulnerability to atrial fibrillation (AF) in a canine model with prolonged rapid atrial pacing.

Materials and Methods: Twenty beagle dogs (weighing 8–10 kg) were randomly assigned to a sham group (n = 6), pacing group (n = 7) and pacing+TRAM-34 group (n = 7). An experimental model of AF was established by rapid pacing. TRAM-34 was administered to the Pacing+TRAM-34 group by slow intravenous injection (10 mg/kg), 3 times each day. After 7 days of pacing, the electrophysiology was measured in vivo. The levels of interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), CD68, c-Fos, p38, and NF-κB p65 in both atriums were measured by Western blotting, and the levels of inducible nitric oxide synthase (iNOS) and arginase1 (Arg-1) were measured by real-time PCR. Macrophage and KCa3.1 in macrophage in the atrium were quantized following double labeled immunofluorescent.

Results: Greater inducibility of AF, an extended duration of AF and lower atrial effective refractory period (AERP) were observed in the pacing group compared with those in the sham group. Both CD68-labeled macrophage and the expression of KCa3.1 in macrophage were elevated in the pacing group and inhibited by TRAM-34, led to higher iNOS expression, lower Arg-1 expression, elevated levels of IL-1β, MCP-1, and TNF-α in the atria, which could be reversed by TRAM-34 treatment (all P < 0.01). KCa3.1 channels were possibly activated via the p38/AP-1/NF-κB signaling pathway.

Conclusions: Inhibition of KCa3.1 suppresses vulnerability to AF by attenuating macrophage pro-inflammatory polarization and inflammatory cytokine secretion in a canine model with prolonged rapid atrial pacing.

The medicinal uses, toxicities and anti-inflammatory activity of Polyalthia species (Annonaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Polyalthia is one of the largest and notable genera in Annonaceae family. Polyalthia species have been widely used in folklore medicine for the treatment of rheumatic fever, gastrointestinal ulcer and generalized body pain. Numerous in vitro and in vivo studies on Polyalthia Species have also corroborated the significant anti-inflammatory potential of its extracts and secondary metabolites.

AIM OF THE STUDY

This review is an attempt to assess the anti-inflammatory activity of Polyalthia species by giving critical appraisal and establishing evidences of their traditional uses. Moreover this review will highlight the lead compounds for future drug development that can serve as a potential anti-inflammatory drug with comparative efficacy and minimum side effects.

MATERIALS AND METHODS

An extensive literature review, focusing the anti-inflammatory potential of Polyalthia species was conducted using the following databases:PubMed, ScienceDirect, SpringerLink, Ovid, Scopus and ProQuest, as well as the locally available books, journals and relevant documents. The reference lists of retrieved papers were also searched for additional studies.

RESULTS

The Polyalthia species have shown significant anti-inflammatory activity through various mechanism of action. The most significant anti-inflammatory mechanism includes the inhibition of nuclear factor kappa B (NF-κB), prostaglandins (PGs), pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and reactive oxygen species (ROS). The data suggests that hydroxycleroda-3,13-dien-15,16-olide and 16-oxocleroda-3,13-dien-15-oic acid, quercetin, rutin, spinasterol, α-spinasterol, goniothalamin and (-)-5-hydroxygoniothalamin are the most potent anti-inflammatory compounds from Polyalthia species with comparable IC₅₀ with positive controls.

CONCLUSIONS

Numerous pharmacological studies have supported the use of Polyalthia species against pain, rheumatic fever, haemorrhages and inflammation in traditional medicine. Flavonoids, diterpenoids, sterols and styrylpyrones from genus Polyalthia are the most significant class of compounds with potent anti-inflammatory activity. Secondary metabolites from these classes should be brought into further research to fill the gaps of knowledge in pharmacokinetics, pharmacodynamics, bioavailability, and toxicity in order to convert the pre-clinical results into clinical data for further investigation.

Structure, Gating and Basic Functions of the Ca2+-activated K Channel of Intermediate Conductance

BACKGROUND

The KCa3.1 channel is the intermediate-conductance member of the Ca2+- activated K channel superfamily. It is widely expressed in excitable and non-excitable cells, where it plays a major role in a number of cell functions. This paper aims at illustrating the main structural, biophysical and modulatory properties of the KCa3.1 channel, and providing an account of experimental data on its role in volume regulation and Ca2+ signals.

METHODS

Research and online content related to the structure, structure/function relationship, and physiological role of the KCa3.1 channel are reviewed.

RESULTS

Expressed in excitable and non-excitable cells, the KCa3.1 channel is voltage independent, its opening being exclusively gated by the binding of intracellular Ca2+ to calmodulin, a Ca2+- binding protein constitutively associated with the C-terminus of each KCa3.1 channel α subunit. The KCa3.1 channel activates upon high affinity Ca2+ binding, and in highly coordinated fashion giving steep Hill functions and relatively low EC50 values (100-350 nM). This high Ca2+ sensitivity is physiologically modulated by closely associated kinases and phosphatases. The KCa3.1 channel is normally activated by global Ca2+ signals as resulting from Ca2+ released from intracellular stores, or by the refilling influx through store operated Ca2+ channels, but cases of strict functional coupling with Ca2+-selective channels are also found. KCa3.1 channels are highly expressed in many types of cells, where they play major roles in cell migration and death. The control of these complex cellular processes is achieved by KCa3.1 channel regulation of the driving force for Ca2+ entry from the extracellular medium, and by mediating the K+ efflux required for cell volume control.

CONCLUSION

Much work remains to be done to fully understand the structure/function relationship of the KCa3.1 channels. Hopefully, this effort will provide the basis for a beneficial modulation of channel activity under pathological conditions.