Toward Defining the Pharmacophore for Positive Allosteric Modulation of PTH1 Receptor Signaling by Extracellular Nucleotides.

The parathyroid hormone 1 receptor (PTH1R) is a Class B G-protein-coupled receptor that is a target for osteoporosis therapeutics. Activated PTH1R couples through Gs to the stimulation of adenylyl cyclase. As well, β-arrestin is recruited to PTH1R leading to receptor internalization and MAPK/ERK signaling.

Extracellular nucleotides enhance agonist potency at the parathyroid hormone 1 receptor.

Parathyroid hormone (PTH) activates the PTH/PTH-related peptide receptor (PTH1R) on osteoblasts and other target cells. Mechanical stimulation of cells, including osteoblasts, causes release of nucleotides such as ATP into the extracellular fluid. In addition to its role as an energy source, ATP serves as an agonist at P2 receptors and an allosteric regulator of many proteins.

P2X7 nucleotide receptor signaling potentiates the Wnt/β-catenin pathway in cells of the osteoblast lineage.

The P2X7 and Wnt/β-catenin signaling pathways regulate osteoblast differentiation and are critical for the anabolic responses of bone to mechanical loading. However, whether these pathways interact to control osteoblast activity is unknown. The purpose of this study was to investigate the effects of P2X7 activation on Wnt/β-catenin signaling in osteoblasts.

Diethyldithiocarbamate-mediated zinc ion chelation reveals role of Cav2.3 channels in glucagon secretion.

Peptide-hormone secretion is partially triggered by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) and gene inactivation of Zn2+-sensitive Cav2.3-type VGCCs is associated with disturbed glucose homeostasis in mice. Zn2+ has been implicated in pancreatic islet cell crosstalk and recent findings indicate that sudden cessation of Zn2+ supply during hypoglycemia triggers glucagon secretion in rodents.

Effects of isoform-selective phosphatidylinositol 3-kinase inhibitors on osteoclasts: actions on cytoskeletal organization, survival, and resorption.

Phosphatidylinositol 3-kinases (PI3K) participate in numerous signaling pathways, and control distinct biological functions. Studies using pan-PI3K inhibitors suggest roles for PI3K in osteoclasts, but little is known about specific PI3K isoforms in these cells. Our objective was to determine effects of isoform-selective PI3K inhibitors on osteoclasts.

P2 receptor networks regulate signaling duration over a wide dynamic range of ATP concentrations.

The primordial intercellular signaling molecule ATP acts through two families of cell-surface P2 receptors - the P2Y family of G-protein-coupled receptors and the P2X family of ligand-gated cation channels. Multiple P2 receptors are expressed in a variety of cell types. However, the significance of these networks of receptors in any biological system remains unknown.

Lysophosphatidic acid: a potential mediator of osteoblast-osteoclast signaling in bone.

Osteoclasts (bone resorbing cells) and osteoblasts (bone forming cells) play essential roles in skeletal development, mineral homeostasis and bone remodeling. The actions of these two cell types are tightly coordinated, and imbalances in bone formation and resorption can result in disease states, such as osteoporosis. Lysophosphatidic acid (LPA) is a potent bioactive phospholipid that influences a number of cellular processes, including proliferation, survival and migration.

Lysophosphatidic acid signals through multiple receptors in osteoclasts to elevate cytosolic calcium concentration, evoke retraction, and promote cell survival.

Lysophosphatidic acid (LPA) is a bioactive phospholipid whose functions are mediated by multiple G protein-coupled receptors. We have shown that osteoblasts produce LPA, raising the possibility that it mediates intercellular signaling among osteoblasts and osteoclasts. Here we investigated the expression, signaling and function of LPA receptors in osteoclasts.

Activation of P2X7 receptors causes isoform-specific translocation of protein kinase C in osteoclasts.

Nucleotides, released in response to mechanical or inflammatory stimuli, signal through P2 nucleotide receptors in many cell types. Osteoclasts express P2X7 receptors (encoded by P2rx7) - Ca(2+)-permeable channels that are activated by high concentrations of extracellular ATP. Genetic disruption of P2rx7 leads to increased resorption and reduced skeletal response to mechanical stimuli.

Extracellular acidification enhances osteoclast survival through an NFAT-independent, protein kinase C-dependent pathway.

Systemic acidosis has detrimental effects on the skeleton and local acidosis is associated with bone destruction in inflammatory and neoplastic diseases. However, the mechanisms by which acidosis enhances osteoclastic bone resorption are poorly understood. Our aim was to examine the effects of acid on osteoclast survival and the involvement of cytosolic Ca(2+) in mediating these effects.

The molecular chaperone hsp70 interacts with the cytosolic II-III loop of the Cav2.3 E-type voltage-gated Ca2+ channel.

Multiple types of voltage-activated Ca2+ channels (T, L, N, P, Q, R type) coexist in excitable cells and participate in synaptic differentiation, secretion, transmitter release, and neuronal plasticity. Ca2+ ions entering cells trigger these events through their interaction with the ion channel itself or through Ca2+ binding to target proteins initiating signalling cascades at cytosolic loops of the ion conducting subunit (Cava1). These loops interact with target proteins in a Ca2+-dependent or independent manner.

The ablation of the Ca(v)2.3/E-type voltage-gated Ca2+ channel causes a mild phenotype despite an altered glucose induced glucagon response in isolated islets of Langerhans.

Glucagon release upon hypoglycemia is an important homeostatic mechanism utilized by vertebrates to restore blood glucose to normal. Glucagon secretion itself is triggered by Ca2+ influx through voltage-gated ion channels, and the gene inactivation of R-type Ca2+ channels, with Ca(v)2.3 as the ion conducting subunit, has been shown to disturb glucose homeostasis.

Convergent signaling by acidosis and receptor activator of NF-kappaB ligand (RANKL) on the calcium/calcineurin/NFAT pathway in osteoclasts.

Systemic acidosis has detrimental effects on the skeleton, and local acidosis coincides with bone destruction in inflammatory and metastatic diseases. Acidification dramatically enhances osteoclastic resorption, although the underlying mechanism has remained elusive. We investigated the effect of acidosis on the osteoclastogenic transcription factor NFATc1, which upon dephosphorylation translocates from the cytoplasm to nuclei.

CaV2.3 calcium channels control second-phase insulin release.

Concerted activation of different voltage-gated Ca( (2+) ) channel isoforms may determine the kinetics of insulin release from pancreatic islets. Here we have elucidated the role of R-type Ca(V)2.3 channels in that process.

The cytosolic II-III loop of Cav2.3 provides an essential determinant for the phorbol ester-mediated stimulation of E-type Ca2+ channel activity.

There is growing evidence that E-type voltage dependent Ca(2+) channels (Ca(v)2.3) are involved in triggering and controlling pivotal cellular processes like neurosecretion and long-term potentiation. The mechanism underlying a novel Ca(2+) dependent stimulation of E-type Ca(2+) channels was investigated in the context of the recent finding that influx of Ca(2+) through other voltage dependent Ca(2+) channels is necessary and sufficient to directly activate protein kinase C (PKC).

Arrhythmia in isolated prenatal hearts after ablation of the Cav2.3 (alpha1E) subunit of voltage-gated Ca2+ channels.

A voltage-gated calcium channel containing Cav2.3e (alpha1Ee) as the ion conducting pore has recently been detected in rat heart. Functional evidence for this Ca2+ channel to be involved in the regulation of heart beating, besides L- and T-type channels, was derived from murine embryos where the gene for Cav1.

Ca2+-sensitive regulation of E-type Ca2+ channel activity depends on an arginine-rich region in the cytosolic II-III loop.

Ca2+-dependent regulation of L-type and P/Q-type Ca2+ channel activity is an important mechanism to control Ca2+ entry into excitable cells. Here we addressed the question whether the activity of E-type Ca2+ channels can also be controlled by Ca2+. Switching from Ba2+ to Ca2+ as charge carrier increased within 50 s, the density of currents observed in HEK-293 cells expressing a human Cav2.

Actions of sipatrigine, 202W92 and lamotrigine on R-type and T-type Ca2+ channel currents.

Relatively little has been published on the pharmacology of R-type and T-type Ca(2+) channels. Here, whole-cell Ca(2+) channel currents were recorded from human embryonic kidney 293 cell-lines transfected with either alpha1E subunits (R-type currents) or alpha1G or alpha1I subunits (T-type currents). R-type currents were inhibited by sipatrigine and the related compound 202W92 (R-(-)-2,4-diamino-6-(fluromethyl)-5-(2,3,5-trichlorophenyl)pyrimidine) with IC(50) 10 and 56 microM, respectively.

Alternate splicing in the cytosolic II-III loop and the carboxy terminus of human E-type voltage-gated Ca(2+) channels: electrophysiological characterization of isoforms.

There is growing evidence that Ca(v)2.3 (alpha1E, E-type) transcripts may encode the ion-conducting subunit of a subclass of R-type Ca(2+) channels, a heterogeneous group of channels by definition resistant to blockers of L-, N-, and P/Q-type Ca(2+) channels. To understand whether splice variation of Ca(v)2.

The Ca(V)2.3 Ca(2+) channel subunit contributes to R-type Ca(2+) currents in murine hippocampal and neocortical neurones.

Different subtypes of voltage-dependent Ca(2+) currents in native neurones are essential in coupling action potential firing to Ca(2+) influx. For most of these currents, the underlying Ca(2+) channel subunits have been identified on the basis of pharmacological and biophysical similarities. In contrast, the molecular basis of R-type Ca(2+) currents remains controversial.

Reduction of insulin secretion in the insulinoma cell line INS-1 by overexpression of a Ca(v)2.3 (alpha1E) calcium channel antisense cassette.

Objective: Multiple types of voltage-activated Ca(2+) channels (T, L, N, P, Q and R type) coordinate a variety of Ca(2+)-dependent processes in neurons and neuroendocrine cells. In insulinoma cell lines as well as in endocrine tissues, the non-L-type alpha1E (Ca(v)2.3) subunit is expressed as the tissue-specific splice variant alpha1Ee.

Disturbances in glucose-tolerance, insulin-release, and stress-induced hyperglycemia upon disruption of the Ca(v)2.3 (alpha 1E) subunit of voltage-gated Ca(2+) channels.

Multiple types of voltage-activated Ca(2+) channels (T, L, N, P, Q, R type) coordinate Ca(2+)-dependent processes in neurons and neuroendocrine cells. Expressional and functional data have suggested a role for Ca(v)2.3 Ca(2+) channels in endocrine processes.

Single-channel pharmacology of mibefradil in human native T-type and recombinant Ca(v)3.2 calcium channels.

To study the molecular pharmacology of low-voltage-activated calcium channels in biophysical detail, human medullary thyroid carcinoma (hMTC) cells were investigated using the single-channel technique. These cells had been reported to express T-type whole-cell currents and a Ca(v)3.2 (or alpha 1H) channel subunit.