The Mitochondrial Voltage-Dependent Anion Channel 1, Ca2+ Transport, Apoptosis, and Their Regulation.

In the outer mitochondrial membrane, the voltage-dependent anion channel 1 (VDAC1) functions in cellular Ca2+ homeostasis by mediating the transport of Ca2+ in and out of mitochondria. VDAC1 is highly Ca2+-permeable and modulates Ca2+ access to the mitochondrial intermembrane space. Intramitochondrial Ca2+ controls energy metabolism by enhancing the rate of NADH production via modulating critical enzymes in the tricarboxylic acid cycle and fatty acid oxidation. Mitochondrial [Ca2+] is regarded as an important determinant of cell sensitivity to apoptotic stimuli and was proposed to act as a "priming signal," sensitizing the organelle and promoting the release of pro-apoptotic proteins. However, the precise mechanism by which intracellular Ca2+ ([Ca2+]i) mediates apoptosis is not known. Here, we review the roles of VDAC1 in mitochondrial Ca2+ homeostasis and in apoptosis. Accumulated evidence shows that apoptosis-inducing agents act by increasing [Ca2+]i and that this, in turn, augments VDAC1 expression levels. Thus, a new concept of how increased [Ca2+]i activates apoptosis is postulated. Specifically, increased [Ca2+]i enhances VDAC1 expression levels, followed by VDAC1 oligomerization, cytochrome c release, and subsequently apoptosis. Evidence supporting this new model suggesting that upregulation of VDAC1 expression constitutes a major mechanism by which apoptotic stimuli induce apoptosis with VDAC1 oligomerization being a molecular focal point in apoptosis regulation is presented. A new proposed mechanism of pro-apoptotic drug action, namely Ca2+-dependent enhancement of VDAC1 expression, provides a platform for developing a new class of anticancer drugs modulating VDAC1 levels via the promoter and for overcoming the resistance of cancer cells to chemotherapy.

Two tarantula venom peptides as potent and differential Na(V) channels blockers.

Voltage dependent sodium (Na(V)) channels are large membrane spanning proteins which lie in the basis of action potential generation and propagation in excitable cells and hence are essential mediators of neuronal signaling. Inhibition of Na(V) channel activity is one of the core mechanisms to treat conditions related to neuronal hyperexcitability, such as epilepsy in the clinic. Na(V) channel blockers are also extensively used to locally inhibit action potential generation and related pain perceptions in the form of local anesthetics. Here we describe the isolation, biochemical characterization, synthesis and in vitro characterization of two potent Na(V) channel blockers from the venom of the Paraphysa scrofa (Phrixotrichus auratus) tarantula spider. Both Voltage sensor toxin 3 (VSTx-3, κ-theraphotoxin-Gr4a) and GTx1-15 (Toxin Gtx1-15), were originally isolated from the venom of the related tarantula Grammostola rosea and described as K(V) and Ca(V) channel blockers, respectively. In our hands, GTx1-15 was shown to be a potent inhibitor of tetrodotoxin (TTX)-sensitive channels (IC50 0.007 µM for hNa(V)1.7 and 0.12 µM for hNa(V)1.3 channels), with very little effect on TTX-resistant (Na(V)1.5 and NaV1.8) channels. VSTx-3 was demonstrated to be a potent, TTX-sensitive sodium channel blocker and especially, potent blocker of Na(V)1.8 channels (IC50 0.19 µM for hNa(V)1.3, 0.43 µM for hNa(V)1.7 and 0.77 µM for hNa(V)1.8 channels). Such potent inhibitors with differential selectivity among Na(V) channel isoforms may be used as tools to study the roles of the different channels in processes related to hyperexcitability and as lead compounds to treat pathological pain conditions.

Using antibodies against P2Y and P2X receptors in purinergic signaling research.

The broad expression pattern of the G protein-coupled P2Y receptors has demonstrated that these receptors are fundamental determinants in many physiological responses, including neuromodulation, vasodilation, inflammation, and cell migration. P2Y receptors couple either G(q) or G(i) upon activation, thereby activating different signaling pathways. Ionotropic ATP (P2X) receptors bind extracellular nucleotides, a signal which is transduced within the P2X protein complex into a cation channel opening, which usually leads to intracellular calcium concentration elevation. As such, this family of proteins initiates or shapes several cellular processes including synaptic transmission, gene expression, proliferation, migration, and apoptosis. The ever-growing range of applications for antibodies in the last 30 years attests to their major role in medicine and biological research. Antibodies have been used as therapeutic tools in cancer and inflammatory diseases, as diagnostic reagents (flow cytometry, ELISA, and immunohistochemistry, to name a few applications), and in widespread use in biological research, including Western blot, immunoprecipitation, and ELISPOT. In this article, we will showcase several of the advances that scientists around the world have achieved using the line of antibodies developed at Alomone Labs for P2Y and P2X receptors.

Kinetics and Gbetagamma modulation of Ca(v)2.2 channels with different auxiliary beta subunits.

Modulation of calcium channels by both auxiliary subunits and G proteins was studied in cell-attached patches from COS-7 cells transfected with Ca(v)2.2 channel subunits (N-type, alpha(1)B and either beta(1b) or beta(2a)). These were co-expressed with either Gbeta(1)gamma(2) or the Gbetagamma-binding domain of beta-adrenergic-receptor kinase-1 to sequester endogenous Gbetagamma. Since G protein modulation of Ca(v) channels may affect both inactivation and activation, we examined Gbetagamma modulation of Ca(v)2.2 channels in the presence of two different beta-subunits that affect inactivation differently and compared in detail the single-channel characteristics of N-type channels expressed with either of these beta-subunit isoforms. The single-channel mean amplitude and mean open time were not influenced by the transfection combination. However, the mean closed time at +40 mV was increased for both beta(1b) and beta(2a)-subunits by co-transfection with Gbeta(1)gamma(2). This effect was absent at lower voltages as examined for channels with the beta(1b)-subunit. The distribution of latency-to-first-opening of Ca(v)2.2 channels was similar for both beta-subunit isoforms. However, the inclusion of the beta(2a) subunit resulted in channels with an additional, prominent, slow activation phase. Co-transfection of Gbeta(1)gamma(2) with Ca(v)2.2 channels markedly reduced the ensemble current amplitude and slowed the first latency. The inhibition imposed by Gbeta(1)gamma(2) was largely independent of the beta-subunit species. Facilitation of Gbetagamma-modulated currents (the channel response following a large and brief depolarising prepulse) was observed for channels with both beta-subunits and involved mainly enhancement of the activation, as assessed by the faster first latency. The inactivation process was strongly dependent on the beta-subunit species, with beta(1b) supporting inactivation and beta(2a) reducing this process. This difference was assessed by estimation of both steady-state inactivation (prepulse influence on test pulse responses) and the inactivation time course during depolarisation. At +40 mV, channels with the beta(1b)-subunit had a fast component of inactivation (time constant ~180 ms, 50%) and a slow phase with time constant of approximately 1 s, while the beta(2a)-subunit supported only a very slow inactivation process with time constant of approximately 5 s. Co-transfection of Gbeta(1)gamma(2) with the Ca(v)2.2 channel had no effect on the inactivation properties with either beta-subunit. In summary, we show that the inactivation properties of expressed Ca(v)2.2 channels depend largely on the beta-subunit species and to a minor extent only on the presence or absence of the Gbetagamma modulator. Furthermore, the activation, amplitude, mean open and closed times and G protein modulation of N-type channels were similar for both beta(1b)- and beta(2a)-subunits.

The ducky mutation in Cacna2d2 results in altered Purkinje cell morphology and is associated with the expression of a truncated alpha 2 delta-2 protein with abnormal function.

The mouse mutant ducky, a model for absence epilepsy, is characterized by spike-wave seizures and cerebellar ataxia. A mutation in Cacna2d2, the gene encoding the alpha 2 delta-2 voltage-dependent calcium channel accessory subunit, has been found to underlie the ducky phenotype. The alpha 2 delta-2 mRNA is strongly expressed in cerebellar Purkinje cells. We show that du/du mice have abnormalities in their Purkinje cell dendritic tree. The mutation in alpha 2 delta-2 results in the introduction of a premature stop codon and predicts the expression of a truncated protein encoded by the first three exons of Cacna2d2, followed by 8 novel amino acids. We show that both mRNA and protein corresponding to this predicted transcript are expressed in du/du cerebellum and present in Purkinje cells. Whereas the alpha 2 delta-2 subunit increased the peak current density of the Ca(V)2.1/beta(4) channel combination when co-expressed in vitro, co-expression with the truncated mutant alpha 2 delta-2 protein reduced current density, indicating that it may contribute to the du phenotype.