A solid understanding of the mechanisms governing ligand binding is crucial for rational design of therapeutics targeting the dopamine D receptor (DR). Here, we use G protein-coupled inward rectifier potassium (GIRK) channel activation in oocytes to measure the kinetics of DR antagonism by a series of aripiprazole analogues, as well as the recovery of dopamine (DA) responsivity upon washout. The aripiprazole analogues comprise an orthosteric and a secondary pharmacophore and differ by the length of the saturated carbon linker joining these two pharmacophores.
View Article and Find Full Text PDFBlock of voltage-gated potassium (Kv) channels has been demonstrated to affect neuronal activity described as increasing excitability. The effect has been associated with a closed-state dependent block. However, the block of Kv channels in e.
View Article and Find Full Text PDFBackground: Previous evidence suggests that UNC9994 is a beta-arrestin2-selective agonist at the dopamine D2 receptor, lacking ability both to activate and antagonize G protein-dependent signaling. However, this has only been reported by one laboratory using a single assay.
Methods: We used G protein-coupled inward rectifier potassium channel activation in Xenopus oocytes to investigate UNC9994-induced modulation of G protein-dependent signaling at dopamine D2 receptor and dopamine D3 receptor.
Understanding the relationships between the rates and dynamics of current wave forms under voltage clamp conditions is essential for understanding phenomena such as state-dependence and use-dependence, which are fundamental for the action of drugs used as anti-epileptics, anti-arrhythmics, and anesthetics. In the present study, we mathematically analyze models of blocking mechanisms. In previous experimental studies of potassium channels we have shown that the effect of local anesthetics can be explained by binding to channels in the open state.
View Article and Find Full Text PDFThe muscarinic M receptor (MR) has been shown to display voltage-sensitive agonist binding, based on G protein-activated inward rectifier potassium channel (GIRK) opening and radioligand binding at different membrane voltages. A conserved aspartate in transmembrane segment (TM) II of MR, D69, has been proposed as the voltage sensor. While a recent paper instead presented evidence of tyrosines in TMs III, VI, and VII acting as voltage sensors, these authors were not able to record GIRK channel activation by a D69N mutant MR.
View Article and Find Full Text PDFThe transmembrane voltage needed to open different voltage-gated K (Kv) channels differs by up to 50 mV from each other. In this study we test the hypothesis that the channels' voltage dependences to a large extent are set by charged amino-acid residues of the extracellular linkers of the Kv channels, which electrostatically affect the charged amino-acid residues of the voltage sensor S4. Extracellular cations shift the conductance-versus-voltage curve, G(V), by interfering with these extracellular charges.
View Article and Find Full Text PDFNewer, "atypical" antipsychotics carry a lower risk of motor side-effects than older, "typical" compounds. It has been proposed that a ~100-fold faster dissociation from the dopamine D2 receptor (D2R) distinguishes atypical from typical antipsychotics. Furthermore, differing antipsychotic D2R affinities have been suggested to reflect differences in dissociation rate constants (koff), while association rate constants (kon) were assumed to be similar.
View Article and Find Full Text PDFBackground: Increased nociceptive neuronal excitability underlies chronic pain conditions. Various ion channels, including sodium, calcium and potassium channels have pivotal roles in the control of neuronal excitability. The members of the family of G protein-gated inwardly rectifying potassium (GIRK) channels, GIRK1-4, have been implicated in modulating excitability.
View Article and Find Full Text PDFSeveral types of intrinsic dynamics have been identified in brain neurons. Type 1 excitability is characterized by a continuous frequency-stimulus relationship and, thus, an arbitrarily low frequency at threshold current. Conversely, Type 2 excitability is characterized by a discontinuous frequency-stimulus relationship and a nonzero threshold frequency.
View Article and Find Full Text PDFIt has been suggested that the favorable side-effect profiles of atypical antipsychotics (e.g. clozapine and amisulpride) are related to their ∼100-fold faster dissociation from dopamine D2 receptors (D2R) compared with typical antipsychotics (e.
View Article and Find Full Text PDFDiabetic peripheral neuropathy (DPN) is the most common complication in both type 1 and type 2 diabetes. Here we studied some phenotypic features of a well-established animal model of type 2 diabetes, the leptin receptor-deficient db(-)/db(-) mouse, and also the effect of long-term (6 mo) treatment with coenzyme Q10 (CoQ10), an endogenous antioxidant. Diabetic mice at 8 mo of age exhibited loss of sensation, hypoalgesia (an increase in mechanical threshold), and decreases in mechanical hyperalgesia, cold allodynia, and sciatic nerve conduction velocity.
View Article and Find Full Text PDFBiochim Biophys Acta
December 2012
Agonist potency at some neurotransmitter receptors has been shown to be regulated by voltage, a mechanism which has been suggested to play a crucial role in the regulation of neurotransmitter release by inhibitory autoreceptors. Likewise, receptor deactivation rates upon agonist removal have been implicated in autoreceptor function. Using G protein-coupled potassium (GIRK) channel activation in Xenopus oocytes as readout of receptor activity, we have investigated the voltage sensitivities and signaling kinetics of the hH(3)(445) and hH(3)(365) isoforms of the human histamine H₃ receptor, which functions as an inhibitory auto- and heteroreceptor in the nervous system.
View Article and Find Full Text PDFVoltage sensitivity has been demonstrated for some GPCRs. At the dopamine D(2S) receptor, this voltage sensitivity is agonist-specific; some agonists, including dopamine, exhibit decreased potency at depolarized potentials, whereas others are not significantly affected. In the present study, we examined some of the receptor-agonist interactions contributing to these differences, and investigated how dopamine D(2S) receptor voltage sensitivity affects clinically used dopamine agonists.
View Article and Find Full Text PDFThe aim of the present study was to clarify the identity of slow spontaneous currents, the underlying mechanism and possible role for impulse generation in neurons of the rat medial preoptic nucleus (MPN). Acutely dissociated neurons were studied with the perforated patch-clamp technique. Spontaneous outward currents, at a frequency of approximately 0.
View Article and Find Full Text PDFThe threshold firing frequency of a neuron is a characterizing feature of its dynamical behaviour, in turn determining its role in the oscillatory activity of the brain. Two main types of dynamics have been identified in brain neurons. Type 1 dynamics (regular spiking) shows a continuous relationship between frequency and stimulation current (f-I(stim)) and, thus, an arbitrarily low frequency at threshold current; Type 2 (fast spiking) shows a discontinuous f-I(stim) relationship and a minimum threshold frequency.
View Article and Find Full Text PDFAdenosine A(2A) receptors (A(2A)Rs) and dopamine D(2) receptors (D(2)Rs) form constitutive heteromers in living cells and exhibit a strong functional antagonistic interaction. Recent findings give neurochemical evidence that extended cocaine self-administration in the rat give rise to an up-regulation of functional A(2A)Rs in the nucleus accumbens that return to baseline expression levels during cocaine withdrawal. In the present work, the acute in vitro effects of a concentration of cocaine known to fully block the dopamine (DA) transporter without exerting any toxic actions were investigated on A(2A)R and D(2L)R formed heteromers in transiently co-transfected HEK-293T cells.
View Article and Find Full Text PDFBiochem Biophys Res Commun
December 2008
Recently, we and others have shown that agonist potencies at some, but not all, G protein-coupled receptors are voltage-sensitive. Several of those studies employed electrophysiology assays in Xenopus oocytes with G protein-coupled potassium channels as a readout. Using this assay, we have now obtained evidence that voltage-sensitivity at the dopamine D(2S) receptor is agonist-specific.
View Article and Find Full Text PDFLocal anesthetics bind to ion channels in a state-dependent manner. For noninactivating voltage-gated K channels the binding mainly occurs in the open state, while for voltage-gated inactivating Na channels it is assumed to occur mainly in inactivated states, leading to an allosterically caused increase in the inactivation probability, reflected in a negative shift of the steady-state inactivation curve, prolonged recovery from inactivation, and a frequency-dependent block. How local anesthetics bind to N-type inactivating K channels is less explored.
View Article and Find Full Text PDFBiochem Biophys Res Commun
September 2008
Agonist potency at some neurotransmitter receptors has been shown to be regulated by transmembrane voltage, a mechanism which has been suggested to play a crucial role in the regulation of neurotransmitter release by autoreceptors and in synaptic plasticity. We have recently described the voltage-sensitivity of the dopamine D(2L) receptor and we now extend our studies to include the other members of the D(2)-like receptor subfamily; the D(2S), D(3), and D(4) dopamine receptors. Electrophysiological recordings were performed on Xenopus oocytes coexpressing human dopamine D(2S), D(3), or D(4) receptors with G protein-coupled potassium (GIRK) channels.
View Article and Find Full Text PDFThe recently cloned histamine H(4) receptor is expressed predominantly in haematopoietic cells and has been found to modulate the function of mast cells, eosinophils, dendritic cells and T lymphocytes. It represents an attractive target for pharmacological interventions against a number of inflammatory and autoimmune disorders. In the present work we used two-electrode voltage-clamp to demonstrate histamine H(4) receptor modulation of G protein-coupled inward rectifier potassium (GIRK) channels heterologously expressed in Xenopus oocytes.
View Article and Find Full Text PDFThe dopamine D2 receptor plays a critical role in activity-dependent synaptic plasticity in the striatum, and regulates the transitions between different states of electrical activity. The D2 receptor is the main target for antipsychotics, and its affinity towards dopamine has been shown to be increased in psychotic patients. Recently, voltage-sensitivity has been reported for the ligand binding and G protein-coupling properties of some neurotransmitter receptors, raising the question whether the D2 receptor is also regulated by voltage.
View Article and Find Full Text PDFIon permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K(+) ion. In the cardiac human ether-a-go-go-related gene channel, which exhibits slow activation and fast inactivation, the corresponding residue is tyrosine.
View Article and Find Full Text PDFBiological systems are organized in intricate and highly structured networks with hierarchies and multiple scales. Cells can be considered as "meso-scale level" systems placed between the "macro-scale level" (systems of cellular networks) and the "micro-scale level" (systems of molecular networks). In fact, cells represent complex biochemical machineries made by networks of molecules connected by biochemical reactions.
View Article and Find Full Text PDFVoltage-gated ion channels are key players in fast neuronal signalling. Detailed knowledge about channel gating is essential for our understanding of channel function in general and of drug action of channels in particular. Despite a number of recent atomic channel structures, the opening of voltage-gated channels is the subject of heated debates.
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