Mitochondria and light: An overview of the pathways triggered in skin and retina with incident infrared radiation

Slightly more than half of the solar radiation that passes through the atmosphere and reaches the Earth's surface is infrared. Over the past few years, many papers have been published on the possible positive effects of receiving this part of the electromagnetic spectrum. In this article we analyse the role of mitochondria in the supposed effects of infrared light based on the published literature. It is claimed that ATP synthesis is stimulated, which has a positive effect on the skin by increasing fibroblast proliferation, anchorage and production of collagen fibres, procollagen, and various cytokines responsible for the wound healing process, such as keratinocyte growth factor. Currently there are infrared light emitting equipment whose manufacturers and the centres where this service or treatment is offered claim that they are used for skin rejuvenation among other positive effects. Based on the literature review, it is necessary to deepen the scientific study of the mechanism of absorption of infrared radiation through the skin to better understand its possible positive effects, the risks of overexposure and to improve consumer health protection.

Hydroxysafflor yellow A actives BKCa channels and inhibits L-type Ca channels to induce vascular relaxation

Hydroxy-safflor yellow A (HSYA) can exert a variety of effects upon the vascular system. However, the underlying mechanisms are not clear. The present study is to investigate its vasodilating effect and the mechanisms. Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were enrolled for studying effects of HSYA on blood pressure, vasodilation, intracellular Ca²⁺ transient and membrane ion channels. Vasodilation and intracellular Ca²⁺ transient were measured by using vasomotor assay and fluorescence imaging system, respectively. The effect of HSYA on the large conductance Ca²⁺ activated and voltage-gated potassium channel (BK_Ca channel) currents in rat mesentery artery and on L-type calcium channel (Ca-L) currents in HEK293cells expressed with Ca-L were investigated using patch clamp techniques. Blood pressure of SHR and WKY rats were concentration dependently reduced by HSYA with a larger effect of HSYA in SHR than that in WKY rats. The tension of mesenteric arteries induced by 3 μM phenylephrine was attenuated by HSYA (IC₅₀ = 90.8 μΜ). Patch clamp study showed that HSYA could activate BK_Ca channels and suppress Ca-L channels in a concentration dependent manner. The results of calcium signaling assays indicated that HSYA could reduce the intracellular free Ca²⁺ level. These findings demonstrate that HSYA could activate BK_Ca channels and inhibit Ca-L channels and reduce intracellular free Ca²⁺ level, which are probably important for its vasodilatory effect.

Effects of miR-200b-3p inhibition on the TRPC6 and BKCa channels of podocytes

Transient receptor potential canonical 6 (TRPC6) and large-conductance Ca²⁺-activated K⁺ channels (BK_Ca), two of the key ion channels for blood filtration function of podocytes, have been implicated in the pathogenesis of kidney diseases. Moreover, it has been reported that miR-200 b plays an important role in regulating the biological processes of podocytes. In this study, we aimed to examine whether there was a relationship between miR-200 b-3p and the two ion channels. It was suggested that miR-200 b-3p down-regulation inhibited the currents of TRPC6 and BK_Ca channels. It also showed that miR-200 b-3p inhibition reduced the levels of protein expression and mRNA transcription of TRPC6 and BK_Ca channels. Moreover, the down-regulation of miR-200 b-3p resulted in the decrease of the intracellular Ca²⁺ concentration. It was also suggested that the decrease of BK_Ca currents resulting from miR-200 b-3p inhibition could be regulated by TRPC6 channels. TRPC6 blockage also inhibited BK_Ca currents and reduced the level of BK_Ca expression. These results together suggested that miR-200 b-3p inhibition reduced the currents of TRPC6, which led to the decrease of intracellular Ca²⁺ concentration. The decrease of Ca²⁺ source required for BK_Ca activation may result in the inhibition of BK_Ca currents.

Mechanosensitivity of mitochondrial large-conductance calcium-activated potassium channels

Potassium channels have been discovered in the inner mitochondrial membrane of various cells. These channels can regulate the mitochondrial membrane potential, the matrix volume, respiration and reactive species generation. Therefore, it is believed that their activation is cytoprotective in various tissues. In our study, the single-channel activity of a large-conductance calcium-activated potassium channel (mitoBK_Ca) was measured by the patch-clamp technique on mitoplasts derived from mitochondria isolated from human glioma U-87 MG cells. Here, we show for the first time that mechanical stimulation of mitoBK_Ca channels results in an increased probability of channel opening. However, the mechanosensitivity of mitoBK_Ca channels was variable with some channels exhibiting no mechanosensitivity. We detected the expression of mechanosensitive BK_Ca-STREX exon in U-87 MG cells and hypotesize, based on previous studies demonstrating the presence of multiple BK_Ca splice variants that variable mechanosensitivity of mitoBK_Ca could be the result of the presence of diverse BK_Ca isoforms in mitochondria of U-87 MG cells. Our findings indicate the possible involvement of the mitoBK_Ca channel in mitochondria activities in which changes in membrane tension and shape play a crucial role, such as fusion/fission and cristae remodeling.

Mechanism of adrenomedullin 2/intermedin mediated vasorelaxation in rat main pulmonary artery

Adrenomedullin 2/intermedin (AM2/IMD) is a member of calcitonin related gene peptide family and an important nitric oxide mediated vasorelaxant in various vascular beds. However, the mechanism of post receptor-interaction is not clear and may differ depending on tissue type and species. In this study, we aimed to investigate the exact mechanism and the role of BK_Ca and calcium channels on the vasorelaxant effect of AM2/IMD in rat PA. Changes in the AM2/IMD-mediated vasorelaxation were evaluated in the presence of various inhibitors. CGRP_(8-37) (10^-6 M), L-NAME (10^-4 M), ODQ (10^-5 M), SQ22536 (10^-4 M), H89 (10^-6 M), TEA (10^-2 M), iberiotoxin (3 × 10^-7 M), and verapamil (10^-5 M), all partly or completely inhibited the vasorelaxation. The relaxation was also abolished by removal of the endothelium, or in KCl precontracted PAs. AM2/IMD did not elicit vasorelaxation in the Ca²⁺-free conditions. However, the vasorelaxation was not inhibited with AM_(22-52) (10^-6 M), 4-AP (3 × 10^-3 M), glibenclamide (10^-5 M), apamin (3 × 10^-7 M), TRAM-34 (10^-5 M), and La⁺³ (10^-4 M). AM2/IMD -induced changes in intracellular calcium levels and isometric force were monitored simultaneously in fura-2-loaded, endothelium-intact PAs. The AM2/IMD-induced increase in intracellular Ca²⁺ concentration was inhibited in the presence of iberiotoxin and verapamil, whereas no change was observed with La³⁺ incubation. Our data suggest that the cAMP/PKA pathway is one of the important pathways AM2/IMD-induced vasorelaxation. AM2/IMD acts through activation of endothelial BK_Ca and subsequently causes hyperpolarization of the endothelial cell membrane. The hyperpolarization induces Ca²⁺ influx, which leads to NO production and subsequent vasorelaxation.

ATP-sensitive and maxi potassium channels regulate BRL 37344-induced tocolysis in buffaloes-an in vitro study

Cellular coupling of beta₃-adrenoceptors (β₃-ADR) to potassium channels in myometrium is largely unknown. In vitro study was undertaken to unravel the presence of β₃-adrenergic receptors (ADR) and the role of K⁺-channels in mediating β₃-ADR-induced relaxation in isolated myometrial strips from cyclic non-pregnant water buffaloes. Isometric tension was recorded in isolated myometrial strips using data acquisition system based physiograph. Compared to SR 59230A, BRL 37344 was found to be more potent in inducing β₃-dependent myometrial relaxation which was significantly (p < 0.05) inhibited in the presence of β₃ antagonist, SAR 150640. The immunoreactive protein to β₃-ADR was also detected in membrane fraction of myometrial protein. Further, incubation with BRL 37344 (10 μM) significantly (p < 0.05) increased c-AMP accumulation (37.58 ± 9.52 pmol/mg protein; n = 4) in the myometrial strips compared to basal c-AMP level (16.85 ± 3.87 pmol/mg protein; n = 4). The concentration response curves (CRC) of BRL 37344 were significantly (p < 0.05) shifted towards right in the presence of K_ATP channels specific blocker, glibenclamide (10 μM) and maxi K⁺-channels (BK_Ca) specific blocker, iberiotoxin (100 nM), with decrease in both efficacy and potency as compared to control. However, 4-aminopyridine (4-AP), a specific blocker of the voltage gated K⁺-channels (Kv), failed to alter the CRC of BRL 37344. Existence of immunoreactive protein to Kir6.1, α-subunit of BK_Ca and Kv1.1 channels were also detected in the membrane fraction of myometrial protein. Based on the above findings, it can be concluded that BRL 37344 is a potent stimulator of β₃-adrenoceptors in buffalo myometrium and besides mediating their effect through rise in c-AMP, they are coupled to K_ATP and BK_Ca channels in inducing tocolytic effects.

BK Channels in the Vertebrate Inner Ear

The perception of complex acoustic stimuli begins with the deconstruction of sound into its frequency components. This spectral processing occurs first and foremost in the inner ear. In vertebrates, two very different strategies of frequency analysis have evolved. In nonmammalian vertebrates, the sensory hair cells of the inner ear are intrinsically electrically tuned to a narrow band of acoustic frequencies. This electrical tuning relies on the interplay between BK channels and voltage-gated calcium channels. Systematic variations in BK channel density and kinetics establish a gradient in electrical resonance that enables the coding of a broad range of acoustic frequencies. In contrast, mammalian hair cells are extrinsically tuned by mechanical properties of the cochlear duct. Even so, mammalian hair cells also express BK channels. These BK channels play critical roles in various aspects of mammalian auditory signaling, from developmental maturation to protection against acoustic trauma. This review summarizes the anatomical localization, biophysical properties, and functional contributions of BK channels in vertebrate inner ears. Areas of future research, based on an updated understanding of the biology of both BK channels and the inner ear, are also highlighted. Investigation of BK channels in the inner ear continues to provide fertile research grounds for examining both BK channel biophysics and the molecular mechanisms underlying signal processing in the auditory periphery.

MaxiK channel interactome reveals its interaction with GABA transporter 3 and heat shock protein 60 in the mammalian brain

Large conductance voltage and calcium-activated potassium (MaxiK) channels are activated by membrane depolarization and elevated cytosolic Ca(2+). In the brain, they localize to neurons and astrocytes, where they play roles such as resetting the membrane potential during an action potential, neurotransmitter release, and neurovascular coupling. MaxiK channels are known to associate with several modulatory proteins and accessory subunits, and each of these interactions can have distinct physiological consequences. To uncover new players in MaxiK channel brain physiology, we applied a directed proteomic approach and obtained MaxiK channel pore-forming α subunit brain interactome using specific antibodies. Controls included immunoprecipitations with rabbit immunoglobulin G (IgG) and with anti-MaxiK antibodies in wild type and MaxiK channel knockout mice (Kcnma1(-/-)), respectively. We have found known and unreported interactive partners that localize to the plasma membrane, extracellular space, cytosol and intracellular organelles including mitochondria, nucleus, endoplasmic reticulum and Golgi apparatus. Localization of MaxiK channel to mitochondria was further confirmed using purified brain mitochondria colabeled with MitoTracker. Independent proof of MaxiK channel interaction with previously unidentified partners is given for GABA transporter 3 (GAT3) and heat shock protein 60 (HSP60). In human embryonic kidney 293 cells containing SV40 T-antigen (HEK293T) cells, both GAT3 and HSP60 coimmunoprecipitated and colocalized with MaxiK channel; colabeling was observed mainly at the cell periphery with GAT3 and intracellularly with HSP60 with protein proximity indices of ∼ 0.6 and ∼ 0.4, respectively. In rat primary hippocampal neurons, colocalization index was identical for GAT3 (∼ 0.6) and slightly higher for HSP60 (∼ 0.5) association with MaxiK channel. The results of this study provide a complete interactome of MaxiK channel the mouse brain, further establish the localization of MaxiK channel in the mouse brain mitochondria and demonstrate the interaction of MaxiK channel with GAT3 and HSP60 in neurons. The interaction of MaxiK channel with GAT3 opens the possibility of a role of MaxiK channel in GABA homeostasis and signaling.

Relaxant effect of flavonoid naringenin on contractile activity of rat colonic smooth muscle

ETHNOPHARMACOLOGICAL RELEVANCE

Disturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility.

MATERIAL AND METHODS

Mechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca(2+)] concentration ([Ca(2+)]i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo.

RESULTS

Naringenin induced a concentration-dependent inhibition (1-1000 μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca(2+) influx induced contraction and [Ca(2+)]i increase were inhibited by naringenin (100 μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K(+) (BKCa) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BKCa current, which was insensitive to changes in the [Ca(2+)]i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo.

CONCLUSION

Our results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BKCa channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca(2+) influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.