Paracetamol inhibits Ca2+ permeant ion channels and Ca2+ sensitization resulting in relaxation of precontracted airway smooth muscle

The purpose of this study was to screen a bronchodilator from old drugs and elucidate the underlying mechanism. Paracetamol (acetaminophen) is a widely used analgesic and antipyretic drug. It has been reported that it inhibits the generation of prostaglandin and histamine, which play roles in asthma. These findings led us to explore whether paracetamol could be a potential bronchodilator. Paracetamol inhibited high K⁺- and acetylcholine (ACH)-induced precontraction of mouse tracheal and bronchial smooth muscles. Moreover, the ACH-induced contraction was partially inhibited by nifedipine (selective blocker of LVDCCs), YM-58483 (selective inhibitor of store-operated Ca²⁺ entry (SOCE), canonical transient receptor potential 3 (TRPC3) and TRPC5 channels) and Y-27632 (selective blocker of ROCK, a linker of the Ca²⁺ sensitization pathway). In single airway smooth muscle cells, paracetamol blocked the currents sensitive to nifedipine and YM-58483, and inhibited intracellular Ca²⁺ increases. In addition, paracetamol inhibited ACH-induced phosphorylation of myosin phosphatase target subunit 1 (MYPT1, another linker of the Ca²⁺ sensitization pathway). Finally, in vivo paracetamol inhibited ACH-induced increases of mouse respirator system resistance. Collectively, we conclude that paracetamol inhibits ASM contraction through blocking LVDCCs, SOCE and/or TRPC3 and/or TRPC5 channels, and Ca²⁺ sensitization. These results suggest that paracetamol might be a new bronchodilator.

Inhibition of antigen receptor-dependent Ca(2+) signals and NF-AT activation by P2X7 receptors in human B lymphocytes

One of the first intracellular signals after antigen binding by the antigen receptor of B lymphocytes is the increased intracellular Ca(2+) concentration ([Ca(2+)]i), which is followed by several intracellular signaling events like the nuclear translocation of the transcription factor NF-AT controlling the fate of B lymphocytes after their activation. Extracellular ATP, which is released from cells under several pathological conditions, is considered a danger-associated signal serving as an immunomodulator. We investigated the interaction of antigen receptor (BCR) and P2X7 receptor (P2X7R) activation on [Ca(2+)]i signaling and on nuclear translocation of the transcription factor NF-AT in human B lymphocytes. Although the P2X7R is an ATP-gated Ca(2+)-permeable ion channel, P2X7R activation inhibits the BCR-mediated [Ca(2+)]i responses. This effect is mimicked by cell membrane depolarization induced by an increase in the extracellular K(+) concentration or by application of the Na(+) ionophore gramicidin, but is abolished by stabilization of the membrane potential using the K(+) ionophore valinomycin, by extracellular Mg(2+), which is known to inhibit P2X7R-dependent effects, or by replacing Na(+) by the less P2X7R-permeable Tris(+) ion. Furthermore, P2X7R activation by ATP inhibits the BCR-dependent translocation of the transcription factor NF-ATc1 to the nucleus. We therefore conclude that extracellular ATP via the P2X7R mediates inhibitory effects on B cell activation. This may be of relevance for understanding of the activation of the BCR under pathological conditions and for the development of therapeutic strategies targeting human B lymphocytes or P2X7 receptors.

Orai1 and STIM1 are critical for cell migration and proliferation of clear cell renal cell carcinoma

The intracellular Ca(2+) regulation has been implicated in tumorigenesis and tumor progression. Notably, store-operated Ca(2+) entry (SOCE) is a major Ca(2+) entry mechanism in non-excitable cells, being involved in cell proliferation and migration in several types of cancer. However, the expression and biological role of SOCE have not been investigated in clear cell renal cell carcinoma (ccRCC). Here, we demonstrate that Orai1 and STIM1, not Orai3, are crucial components of SOCE in the progression of ccRCC. The expression levels of Orai1 in tumor tissues were significantly higher than those in the adjacent normal parenchymal tissues. In addition, native SOCE was blunted by inhibiting SOCE or by silencing Orai1 and STIM1. Pharmacological blockade or knockdown of Orai1 or STIM1 also significantly inhibited RCC cell migration and proliferative capability. Taken together, Orai1 is highly expressed in ccRCC tissues illuminating that Orai1-mediated SOCE may play an important role in ccRCC development. Indeed, Orai1 and STIM1 constitute a native SOCE pathway in ccRCC by promoting cell proliferation and migration.

Store-operated calcium entry induced by activation of Gq-coupled alpha1B adrenergic receptor in human osteoblast

Recent studies have revealed that the sympathetic nervous system is involved in bone metabolism. We previously reported that noradrenaline (NA) suppressed K(+) currents via Gi/o protein-coupled alpha1B-adrenergic receptor (α1B-AR) in human osteoblast SaM-1 cells. Additionally, it has been demonstrated that the intracellular Ca(2+) level ([Ca(2+)]i) was increased by NA via α1B-AR. In this study, we investigated the signal pathway of NA-induced [Ca(2+)]i elevation by using Ca(2+) fluorescence imaging in SaM-1 cells. NA-induced [Ca(2+)]i elevation was suppressed by pretreatment with a PLC inhibitor, U73122. This suggested that the [Ca(2+)]i elevation was mediated by Gq protein-coupled α1B-AR. On the other hand, NA-induced [Ca(2+)]i elevation was completely abolished in Ca(2+)-free solution, which suggested that Ca(2+) influx is the predominant pathway of NA-induced [Ca(2+)]i elevation. Although the inhibition of K(+) channel by NA caused membrane depolarization, the [Ca(2+)]i elevation was not affected by voltage-dependent Ca(2+) channel blockers, nifedipine and mibefradil. Meanwhile, NA-induced [Ca(2+)]i elevation was abolished following activation of store-operated Ca(2+) channel by thapsigargin. Additionally, the [Ca(2+)]i elevation was suppressed by store-operated channel inhibitors, 2-APB, flufenamate, GdCl3 and LaCl3. These results suggest that Ca(2+) influx through store-operated Ca(2+) channels plays a critical role in the signal transduction pathway of Gq protein-coupled α1B-AR in human osteoblasts.