Properties of BK(Ca) channels in oral keratinocytes

Enhancing Human Cutaneous Wound Healing through Targeted Suppression of Large Conductance Ca2+-Activated K+ Channels

The modulation of K+ channels plays a crucial role in cell migration and proliferation, but the effect of K+ channels on human cutaneous wound healing (CWH) remains underexplored. This study aimed to determine the necessity of modulating K+ channel activity and expression for human CWH. The use of 25 mM KCl as a K+ channel blocker markedly improved wound healing in vitro (in keratinocytes and fibroblasts) and in vivo (in rat and porcine models). K+ channel blockers, such as quinine and tetraethylammonium, aided in vitro wound healing, while Ba2+ was the exception and did not show similar effects. Single-channel recordings revealed that the Ba2+-insensitive large conductance Ca2+-activated K+ (BKCa) channel was predominantly present in human keratinocytes. NS1619, an opener of the BKCa channel, hindered wound healing processes like proliferation, migration, and filopodia formation. Conversely, charybdotoxin and iberiotoxin, which are BKCa channel blockers, dramatically enhanced these processes. The downregulation of BKCa also improved CWH, whereas its overexpression impeded these healing processes. These findings underscore the facilitative effect of BKCa channel suppression on CWH, proposing BKCa channels as potential molecular targets for enhancing human cutaneous wound healing.

Iberiotoxin and clofilium regulate hyperactivation, acrosome reaction, and ion homeostasis synergistically during human sperm capacitation

Potassium channels play essential roles in the regulation of male fertility. However, potassium channels mediating K⁺ currents in human sperm (I_KSper ) remain controversial. Besides SLO3, the SLO1 potassium channel is a potential candidate for human sperm KSper. This study intends to elucidate the function of SLO1 potassium channel during human sperm capacitation. Human sperm were treated with iberiotoxin (IbTX, a SLO1 specific inhibitor) and clofilium (SLO3 inhibitor) separately or simultaneously during in vitro capacitation. A computer-assisted sperm analyzer was used to assess sperm motility. The sperm acrosome reaction (AR) was analyzed using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Sperm protein tyrosine phosphorylation was studied using western blotting. Intracellular Ca²⁺ , K⁺ , Cl^- , and pH were analyzed using ion fluorescence probes. Independent inhibition with IbTX or clofilium decreased the sperm hyperactivation, AR, and protein tyrosine phosphorylation, and was accompanied by an increase in [K⁺ ]_i , [Cl^- ]_i , and pH_i , but a decrease in [Ca²⁺ ]_i . Simultaneously inhibition with IbTX and clofilium lower sperm hyperactivation and AR more than independent inhibition. The increase in [K⁺ ]_i , [Cl^- ]_i , and pH_i , and the decrease in [Ca²⁺ ]_i were more pronounced. This study suggested that the SLO1 potassium channel may have synergic roles with SLO3 during human sperm capacitation.

Cardiovascular Effects of Caffeic Acid and Its Derivatives: A Comprehensive Review

Caffeic acid (CA) and its phenethyl ester (CAPE) are naturally occurring hydroxycinnamic acids with an interesting array of biological activities; e.g., antioxidant, anti-inflammatory, antimicrobial and cytostatic. More recently, several synthetic analogs have also shown similar properties, and some with the advantage of added stability. The actions of these compounds on the cardiovascular system have not been thoroughly explored despite presenting an interesting potential. Indeed the mechanisms underlying the vascular effects of these compounds particularly need clarifying. The aim of this paper is to provide a comprehensive and up-to-date review on current knowledge about CA and its derivatives in the cardiovascular system. Caffeic acid, CAPE and the synthetic caffeic acid phenethyl amide (CAPA) exhibit vasorelaxant activity by acting on the endothelial and vascular smooth muscle cells. Vasorelaxant mechanisms include the increased endothelial NO secretion, modulation of calcium and potassium channels, and modulation of adrenergic receptors. Together with a negative chronotropic effect, vasorelaxant activity contributes to lower blood pressure, as several preclinical studies show. Their antioxidant, anti-inflammatory and anti-angiogenic properties contribute to an important anti-atherosclerotic effect, and protect tissues against ischemia/reperfusion injuries and the cellular dysfunction caused by different physico-chemical agents. There is an obvious shortage of in vivo studies to further explore these compounds' potential in vascular physiology. Nevertheless, their favorable pharmacokinetic profile and overall lack of toxicity make these compounds suitable for clinical studies.

Multiple regulatory actions of 2-guanidine-4-methylquinazoline (GMQ), an agonist of acid-sensing ion channel type 3, on ionic currents in pituitary GH3 cells and in olfactory sensory (Rolf B1.T) neurons

GMQ (2-guanidine-4-methylquinazoline or N-(4-methyl-2-quinazolinyl)-guanidine hydrochloride), an agonist of acid-sensing ion channel type 3, has been increasingly used for in vivo studies of alternations in nociceptic behavior. In this study, we tried to investigate whether GMQ has any possible effect on other types of ion channels. Addition of GMQ to pituitary GH3 cells raised the amplitude of Ca²⁺-activated K⁺ currents (I_K(Ca)), which was reversed by verruculogen or PF1022A, but not by TRAM-39. Under inside-out current recordings, addition of GMQ into bath enhanced the probability of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels with an EC₅₀ value of 0.95 µM. The activation curve of BK_Ca channels during exposure to GMQ shifted to a lower depolarized potential, with no change in the gating charge of the curve; however, there was a reduction of free energy for channel activation in its presence. As cells were exposed to GMQ, the amplitude of ion currents were suppressed, including delayed rectifying K⁺ current, voltage-gated Na⁺ and L-type Ca²⁺ currents. In Rolf B1.T olfactory sensory neuron, addition of GMQ was able to induce inward current and to suppress peak I_Na. Taken together, findings from these results indicated that in addition to the activation of ASIC3 channels, this compound might directly produce additional actions on various types of ion channels. Caution should be taken in the interpretation of in vivo experimental results when GMQ or other structurally similar compounds are used as targets to characterize the potential functions of ASIC3 channels.

Activation of K(+) channel by 1-EBIO rescues the head and neck squamous cell carcinoma cells from Ca(2+) ionophore-induced cell death

Ion channels in carcinoma and their roles in cell proliferation are drawing attention. Intracellular Ca²⁺ ([Ca²⁺]_i)-dependent signaling affects the fate of cancer cells. Here we investigate the role of Ca²⁺-activated K⁺ channel (SK4) in head and neck squamous cell carcinoma cells (HNSCCs) of different cell lines; SNU-1076, OSC-19 and HN5. Treatment with 1 µM ionomycin induced cell death in all the three cell lines. Whole-cell patch clamp study suggested common expressions of Ca²⁺-activated Cl^- channels (Ano-1) and Ca²⁺-activated nonselective cation channels (CAN). 1-EBIO, an activator of SK4, induced outward K⁺ current (ISK4) in SNU-1076 and OSC-19. In HN5, ISK4 was not observed or negligible. The 1-EBIO-induced current was abolished by TRAM-34, a selective SK4 blocker. Interestingly, the ionomycin-induced cell death was effectively prevented by 1-EBIO in SNU-1076 and OSC-19, and the rescue effect was annihilated by combined TRAM-34. Consistent with the lower level of ISK4, the rescue by 1-EBIO was least effective in HN5. The results newly demonstrate the role of SK4 in the fate of HNSCCs under the Ca²⁺ overloaded condition. Pharmacological modulation of SK4 might provide an intriguing novel tool for the anti-cancer strategy in HNSCC.

Arecoline inhibits intermediate-conductance calcium-activated potassium channels in human glioblastoma cell lines

Arecoline (ARE) is an alkaloid-type natural product from areca nut. This compound has numerous pharmacological and toxicological effects. Whether this agent interacts with ion channels to perturb functional activity of cells remains unknown. The effects of ARE on ionic currents were studied in glioma cell lines (U373 and U87MG) using patch-clamp technique. Like TRAM-34(1-[(2-chlorophenyl)-diphenylmethyl]pyrazole), ARE suppressed the amplitude of whole-cell voltage-gated K(+) currents in U373 cells elicited by a ramp voltage clamp. In cell-attached configuration, ARE did not modify the single-channel conductance of intermediate-conductance Ca(2+)-activated K(+) (IKCa) channels; however, it did reduce channel activity. Its inhibition of IKCa channels was accompanied by a significant lengthening in the slow component of mean closed time of IKCa channels. Based on minimal kinetic scheme, the dissociation constant (KD) required for ARE-mediated prolongation of mean closed time was 11.2µM. ARE-induced inhibition of IKCa channels was voltage-dependent. Inability of ARE to perturb the activity of large-conductance Ca(2+)-activated K(+) (BKCa) channels was seen. Under current-clamp recordings, ARE depolarized the membrane of U373 cells and DCEBIO reversed ARE-induced depolarization. Similarly, ARE suppressed IKCa-channel activities in oral keratinocytes. This study provides the evidence that ARE block IKCa channels in a concentration, voltage and state-dependent manner. ARE-induced block of IKCa channels is unrelated to the binding of muscarinic receptors. The effects of ARE on these channels may partially be responsible for the underlying cellular mechanisms by which it influences the functional activities of glioma cells or oral keratinocytes, if similar findings occur in vivo.

Kv7/M-type potassium channels in rat skin keratinocytes

Skin keratinocytes fulfil important signalling and protective functions. Immunocytochemical experiments revealed the unexpected presence of immunoreactivity for the M-type potassium channel subunit Kv7.2 in the keratinocyte layer of intact rat paw skin and in keratinocytes isolated from the skin of 1-day-old rats and cultured in vitro for 3–10 days. Application of the M-channel enhancer retigabine (3–10 μM) to isolated cultured rat keratinocytes: (a) increased outward membrane currents recorded under voltage clamp, (b) produced ~3 mV hyperpolarization at rest, (c) enhanced ~3-fold the release of ATP induced by the TRPV3 agonist carvacrol (1 mM) and (d) increased the amplitude of the carvacrol-induced intracellular Ca²⁺ transient measured with Fura-2. The effect of retigabine on ATP release was prevented by the M-channel blocking agent XE991. We conclude that rat skin keratinocytes possess M-channels that, when activated, can modify their physiological properties, with potential significance for their sensory and other biological functions.

The effects of magnetite (Fe₃O₄) nanoparticles on electroporation-induced inward currents in pituitary tumor (GH₃) cells and in RAW 264.7 macrophages

Aims

Fe₃O₄ nanoparticles (NPs) have been known to provide a distinct image contrast effect for magnetic resonance imaging owing to their super paramagnetic properties on local magnetic fields. However, the possible effects of these NPs on membrane ion currents that concurrently induce local magnetic field perturbation remain unclear.

Methods

We evaluated whether amine surface-modified Fe₃O₄ NPs have any effect on ion currents in pituitary tumor (GH₃) cells via voltage clamp methods.

Results

The addition of Fe₃O₄ NPs decreases the amplitude of membrane electroporation-induced currents (I_MEP) with a half-maximal inhibitory concentration at 45 μg/mL. Fe₃O₄ NPs at a concentration of 3 mg/mL produced a biphasic response in the amplitude of I_MEP, ie, an initial decrease followed by a sustained increase. A similar effect was also noted in RAW 264.7 macrophages.

Conclusion

The modulation of magnetic electroporation-induced currents by Fe₃O₄ NPs constitutes an important approach for cell tracking under various imaging modalities or facilitated drug delivery.

Antifungal drug discovery through the study of invertebrate model hosts

There is an urgent need for new antifungal agents that are both effective and non-toxic in the therapy of systemic mycoses. The model nematode Caenorhabditis elegans has been used both to elucidate evolutionarily conserved components of host-pathogen interactions and to screen large chemical libraries for novel antimicrobial compounds. Here we review the use of C. elegans models in drug discovery and discuss caffeic acid phenethyl ester, a novel antifungal agent identified using an in vivo screening system. C. elegans bioassays allow high-throughput screens of chemical libraries in vivo. This whole-animal system may enable the identification of compounds that modulate immune responses or affect fungal virulence factors that are only expressed during infection. In addition, compounds can be simultaneously screened for antifungal efficacy and toxicity, which may overcome one of the main obstacles in current antimicrobial discovery. A pilot screen for antifungal compounds using this novel C. elegans system identified 15 compounds that prolonged survival of nematodes infected with the medically important human pathogen Candida albicans. One of these compounds, caffeic acid phenethyl ester (CAPE), was an effective antifungal agent in a murine model of systemic candidiasis and had in vitro activity against several fungal species. Interestingly, CAPE is a potent immunomodulator in mammals with several distinct mechanisms of action. The identification of CAPE in a C. elegans screen supports the hypothesis that this model can identify compounds with both antifungal and host immunomodulatory activity.

The vasorelaxant effect of caffeic acid phenethyl ester on porcine coronary artery ring segments

Caffeic acid phenethyl ester (CAPE) is a naturally occurring compound isolated from honeybee propolis whose cardiovascular properties remain uncertain. The purpose of this study was to investigate the possible mechanisms of CAPE-induced vasorelaxation in porcine coronary artery rings. It was found that both the quiescent and precontracted coronary artery ring segments were relaxed by CAPE (10(-7)-10(-)(4) M). N(omega)-nitro-l-arginine (L-NNA), methylene blue and removal of endothelium significantly attenuated CAPE-induced relaxation of both quiescent and precontracted artery rings. This relaxing effect of CAPE on coronary arteries was also significantly reduced by propranolol, and SQ22536, but not by indomethacin. In addition, the dose-response curves of KCl (2.5-100 mM) and CaCl(2) (10(-5)-10(-2) M) were displaced downwards in the presence of CAPE. These results suggest that the relaxant effect of CAPE on porcine coronary artery rings might involve the action of nitric oxide (NO) and adrenergic beta-receptor, together with their second messenger, cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), respectively, but not involve the synthesis of prostaglandin.

Nitric oxide stimulates a large-conductance Ca-activated K+ channel in human skin fibroblasts through protein kinase G pathway

In order to investigate the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel and determine the effects of nitric oxide (NO) on the channel in human skin fibroblasts, we performed electrophysiological patch clamp recordings on 5th-passage cells of human genital skin cultures. The whole-cell outward K(+) current was increased with depolarization, and proved to be sensitive to NS1619 (a selective BK(Ca) channel activator) and iberiotoxin (a specific BK(Ca )channel inhibitor). The single-channel currents showed 226 pS of mean conductance in symmetrical K(+). Sodium nitroprusside (SNP; an NO donor) significantly increased the K(+) current amplitude in the whole-cell mode, and open probability of the channel (NPo) in the cell-attached mode, but not in the inside-out mode. S-nitroso-N-acetylpenicillamine (an NO donor) and 8-Br-cGMP (a membrane-permeant cGMP analogue) also increased the BK(Ca )channel activity. The stimulatory effect of SNP on BK(Ca) channels was inhibited by pretreatment with 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (a soluble guanylyl cyclase inhibitor), or KT5823 [a specific protein kinase G (PKG) inhibitor]. Cytoplasmic PKG also increased the channel activity in inside-out patches. In conclusion, the present data indicate that BK(Ca) channels constitute a significant fraction of K(+) current in human skin fibroblasts, and that NO increases NPo of BK(Ca) channels, which are mediated via the cGMP/PKG pathway, without direct effects on the channel.