Role of voltage-gated calcium channels in potassium-stimulated aldosterone secretion from rat adrenal zona glomerulosa cells

The mineralocorticoid aldosterone plays an important role in the regulation of plasma electrolyte homeostasis. Exposure of acutely isolated rat adrenal zona glomerulosa cells to elevated K(+) activates voltage-gated calcium channels and initiates a calcium-dependent increase in aldosterone synthesis. We developed a novel 96-well format aldosterone secretion assay to rapidly evaluate the effect of known T- and L-type calcium channel antagonists on K(+)-stimulated aldosterone secretion and better define the role of voltage-gated calcium channels in this process. Reported T-type antagonists, mibefradil and Ni(2+), and selected L-type antagonist dihydropyridines, inhibited K(+)-stimulated aldosterone synthesis. Dihydropyridine-mediated inhibition occurred at concentrations which had no effect on rat alpha1H T-type Ca(2+) currents. In contrast, below 10 microM, the L-type antagonists verapamil and diltiazem showed only minimal inhibitory effects. To examine the selectivity of the calcium channel antagonist-mediated inhibition, we established an aldosterone secretion assay in which 8Br-cAMP stimulates aldosterone secretion independent of extracellular calcium. Mibefradil remained inhibitory in this assay, while the dihydropyridines had only limited effects. Taken together, these data demonstrate a role for the L-type calcium channel in K(+)-stimulated aldosterone secretion. Further, they confirm the need for selective T-type calcium channel antagonists to better address the role of T-type channels in K(+)-stimulated aldosterone secretion.     

Modulation of calcium channel function by drugs

Calcium channel blocking drugs, or "calcium antagonists", have been increasingly used in the last decade, both as valuable cardiovascular drugs, and as tools to investigate the pharmacology of the calcium channels which play a vital role in the excitation-activation coupling of many excitable cells. Three important developments, "patch clamping" to investigate single calcium channels, ligand binding studies to investigate the calcium antagonist "receptor sites", and the introduction of novel calcium channel activators, or "calcium agonists", have recently led to greater understanding of the mechanism of action of drugs on the calcium channel. We show here how the calcium channel modulators interact with the binding sites to increase or decrease calcium flux, and hence to modulate the activity of many excitable tissues. We predict that these new developments will soon result in the isolation of purified calcium channels, and investigation of their subtypes and drug sensitivities. This information could lead to the introduction of novel, more selective calcium antagonists for a variety of indications such as atherosclerosis or neurological disorders. Of particular interest is the potential of tissue-selective calcium agonistic drugs to combat cardiac failure or endocrinological disorders.     

Molecular mechanisms and binding site locations for noncompetitive antagonists of nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors are pentameric proteins that belong to the Cys-loop receptor superfamily. Their essential mechanism of functioning is to couple neurotransmitter binding, which occurs at the extracellular domain, to the opening of the membrane-spanning cation channel. The function of these receptors can be modulated by structurally different compounds called noncompetitive antagonists. Noncompetitive antagonists may act at least by two different mechanisms: a steric and/or an allosteric mechanism. The simplest idea representing a steric mechanism is that the antagonist molecule physically blocks the ion channel. On the other hand, there exist distinct allosteric mechanisms. For example, noncompetitive antagonists may bind to the receptor and stabilize a nonconducting conformational state (e.g., resting or desensitized state), and/or increase the receptor desensitization rate. Barbiturates, dissociative anesthetics, antidepressants, and neurosteroids have been shown to inhibit nicotinic receptors by allosteric mechanisms and/or by open- and closed-channel blockade. Receptor modulation has proved to be highly complex for most noncompetitive antagonists. Noncompetitive antagonists may act by more than one mechanism and at distinct sites in the same receptor subtype. The binding site location for one particular molecule depends on the conformational state of the receptor. The mechanisms of action and binding affinities of noncompetitive antagonists differ among nicotinic receptor subtypes. Knowledge of the structure of the nicotinic acetylcholine receptor, the location of its noncompetitive antagonist binding sites, and the mechanisms of inhibition will aid the design of new and more efficacious drugs for treatment of neurological diseases.     

Effects of Temperature and Allosteric Modulators on [3H]Nitrendipine Binding: Methods for Detecting Potential Ca2+ Channel Blockers

Abstract

The effects of incubation temperature and allosteric modulators were studied on [³H]nitrendipine binding to guinea-pig cardiac membranes. Incubation temperature only slightly affected the ability of nifedipine and verapamil derivatives to inhibit binding. By contrast, the Ca²⁺ channel blockers d-cis-diltiazem and fostedil (KB-944) stimulated [³H]nitrendipine binding in a temperature-dependent manner (37° > 25° > 4° C). The stimulatory effect of fostedil could be related to a decrease (2.3-fold at 37° C) in the rate of radioligand binding site dissociation, without significant effects on association kinetics. Both fostedil and d-cis-diltiazem caused a shift to the right of the concentration-inhibition curve of tiapamil, a negative allosteric modulator of [³H]nitrendipine binding. Neither compound affected the ability of nifedipine, a competitive antagonist, to inhibit radioligand binding. This selective effect of fostedil or d-cis-diltiazem may be useful for testing whether potential Ca²⁺ channel blockers interact in a competitive as opposed to allosteric manner with the dihydropyridine site. Varying the incubation temperature may also be useful in detecting compounds which act as positive allosteric modulators (stimulators) of dihydropyridine binding.     

A new class of calcium entry blockers defined by 1,3-diphosphonates. Interactions of SR-7037 (belfosdil) with receptors for calcium channel ligands

Tetrabutyl-2(2-phenoxyethyl)-1,3-propylidene diphosphonate (SR-7037) completely displaced dihydropyridine [( 3H]PN200-110), phenylalkylamine [( 3H]D888), and benzothiazepine [( 3H]diltiazem) ligands from brain L-type calcium channels. Half-maximal inhibition of [3H]PN200-110 binding occurred at 19 nM with a Hill coefficient of 0.96. SR-7037 primarily decreased the affinity for [3H]PN200-110 with a small, but significantly, effect on the maximal binding capacity. Kinetic studies showed that this was due to an increased radioligand dissociation rate from 0.04 min-1 to 0.43 min-1 in the presence of the diphosphonate. Displacement of [3H]D888 by SR-7037 was biphasic with respective IC50 of 44 and 8400 nM. Likewise, unlabeled (-)-D888 identified two sites with IC50 values of 0.9 and 27 nM. Both SR-7037 (1000 nM) and D888 (200 nM) accelerated radioligand dissociation about 2-fold. [3H]Diltiazem binding was inhibited by SR-7037 with an IC50 value of 29 nM. The inhibition of dihydropyridine binding by SR-7037 is enhanced by most divalent cations at millimolar concentrations with the following potency: Mn2+ greater than Mg2+ greater than Ca2+ greater than Co2+. Barium has the opposite effect. The half-maximal effect of calcium occurred at 6 microM free ion. Specific binding of [3H]D888 was antagonized in the presence of 1 mM CaCl2. It is concluded that SR-7037 has allosteric interactions with the dihydropyridine receptor of the L-type calcium channel. The differential effect of Ca2+ on the potency of D888 and diltiazem relative to that of SR-7037 indicates that the three drugs may bind to nonequivalent sites. These results support specific calcium channel inhibition, possibly at a novel site, as the primary mechanism of the diphosphonate's pharmacological actions.     

The mechanism of binding of dihydropyridine calcium channel blockers to rat brain membranes

Detailed kinetic and equilibrium studies of the binding of two radiolabeled 1,4-dihydropyridine calcium antagonists to putative calcium channels in rat brain membranes were performed. (+/-)-[3H]Nitrendipine, a racemic ligand, and (+)-[3H]isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1, 4-dihydro-2,6-dimethyl-5-methoxycarbonylpyridine-3-carboxylate (PN200-110), a pure isomer, were used and their binding properties were quantitated and compared. Analysis of equilibrium binding revealed a single high affinity component for each radioligand with the same density of binding sites for both ligands. Association rates were determined over a 60-fold range of concentration of each radioligand. For both radioligands, the pseudo-first order association time courses were biphasic with the rate of the faster component dependent on radioligand concentration and the rate of the slower component independent of both the structure of the radioligand and the concentration of the radioligand. Dissociation rates were determined after various times of association. The dissociation of the optically pure radioligand, (+)-[3H]PN200-110, was monophasic at all association times, consistent with a single bound species being present throughout association. However, (+/-)-[3H]nitrendipine dissociation was biphasic after short association times (1-10 min). The biphasic dissociation observed with (+/-)-[3H]nitrendipine is consistent with the two optical isomers binding with approximately the same association rate but having different dissociation rates. These results appear to reflect the existence of two interconvertible binding states of the putative calcium channel in the membrane, one which binds the radioligands with high affinity in a simple bimolecular reaction and one which has no detectable affinity for the ligands. This mechanism of isomerization before ligand binding has been modeled by numerical solution of the differential equations of the scheme providing estimates of the rate constants for each reaction in the scheme.     

A Ca(v)3.2/syntaxin-1A signaling complex controls T-type channel activity and low-threshold exocytosis

T-type calcium channels represent a key pathway for Ca(2+) entry near the resting membrane potential. Increasing evidence supports a unique role of these channels in fast and low-threshold exocytosis in an action potential-independent manner, but the underlying molecular mechanisms have remained unknown. Here, we report the existence of a syntaxin-1A/Ca(v)3.2 T-type calcium channel signaling complex that relies on molecular determinants that are distinct from the synaptic protein interaction site (synprint) found in synaptic high voltage-activated calcium channels. This interaction potently modulated Ca(v)3.2 channel activity, by reducing channel availability. Other members of the T-type calcium channel family were also regulated by syntaxin-1A, but to a smaller extent. Overexpression of Ca(v)3.2 channels in MPC 9/3L-AH chromaffin cells induced low-threshold secretion that could be prevented by uncoupling the channels from syntaxin-1A. Altogether, our findings provide compelling evidence for the existence of a syntaxin-1A/T-type Ca(2+) channel signaling complex and provide new insights into the molecular mechanism by which these channels control low-threshold exocytosis.     

Mixed Competitive and Allosteric Antagonism by Gallamine of Muscarinic Receptor-Mediated Second Messenger Responses in N1E-115 Neuroblastoma Cells

The antagonistic effects of gallamine on muscarinic receptor-linked responses were investigated in N1E-115 neuroblastoma cells. M1 muscarinic receptor-mediated phosphoinositide hydrolysis induced by carbamylcholine was antagonized by gallamine, with a Ki value of 33 microM. By comparison, gallamine was four- to fivefold less potent in blocking noncardiac M2 muscarinic receptor-mediated inhibition of cyclic AMP formation, with a Ki value of 144 microM. The resulting Arunlakshana-Schild plots of the antagonism of both responses by gallamine were linear and exhibited slopes not differing from 1, a result indicative of a competitive mechanism. To elucidate further the nature of gallamine's inhibitory actions, experiments were performed where the effects of gallamine in combination with the known competitive muscarinic antagonist, N-methylscopolamine (NMS), were studied. In the presence of both antagonists, a supraadditive shift in the carbamylcholine dose-response curve was demonstrated for the two responses, a result suggestive of an allosteric mode of interaction between gallamine and NMS binding sites. Confirmation that gallamine allosterically modifies the muscarinic receptor was provided by radioligand binding studies. Gallamine competition curves with either [N-methyl-3H]scopolamine methyl chloride ([3H]NMS) or [N-methyl-3H]quinuclidinyl benzilate methyl chloride ([3H]NMeQNB) were unusually shallow. Furthermore, gallamine decelerated the rate of dissociation of receptor-bound [3H]NMS greater than [3H]NMeQNB in a dose-dependent manner. The present study demonstrates that whereas gallamine antagonizes carbamylcholine-mediated responses in N1E-115 cells in a competitive manner, an allosteric component of its action is revealed in the presence of muscarinic antagonists such as NMS.     

Dissociation of Muscimol, SR 95531, and Strychnine from GABAA and Glycine Receptors, Respectively, Suggests Similar Cooperative Interactions

Binding to gamma-aminobutyric acid-A (GABAA) receptors was studied in synaptosomal membranes of rat brain. Dissociation of [3H]muscimol and the GABAA antagonist [3H]2-(3-carboxypropyl)-3-amino-6-p-methoxyphenylpyridazinium bromide ([3H]SR 95531) binding elicited by 100-fold dilution was accelerated by excess of GABA or SR 95531. Control dissociation might be retarded by rebinding. The contribution of a rapid first phase of dissociation of the agonist [3H]muscimol was preferentially enhanced by SR 95531. In contrast, the dissociation of [3H]SR 95531 binding was preferentially accelerated by GABA. These opposite preferential accelerations can be explained by negative heterotropic cooperativity and a reversed affinity relationship of agonists and antagonists to GABAA binding sites with different affinities. Modification of the membranes by p-diazobenzenesulfonic acid (DSA) selectively decreased the accelerating effect of GABA on the dissociation of [3H]SR 95531 binding. [3H]Strychnine binding was studied in a membrane preparation of rat spinal cord. The dissociation of the antagonist [3H]strychnine elicited by dilution was preferentially accelerated by glycine. Again, pretreatment with DSA decreased selectively this negative heterotropic (i.e., allosteric) interaction. Chemical modification by DSA might be attributed to tyrosine residues responsible for similar allosteric interactions for the GABA- and glycine-gated chloride channels.     

Investigation into the structure-activity relationship of novel concentration dependent, dual action T-type calcium channel agonists/antagonists

This paper describes the synthesis and biological evaluation of a series of straight chain analogs of a compound (1) that was previously synthesized in our research program. These compounds, which are T-type calcium channel antagonists, exhibits potent anti-proliferative activity against a variety of cancer cells. A structure-activity relationship of these analogs against a variety of cancer cells has provided insight into a logical pharmacophore for this series of compounds. Furthermore, this series of compounds has presented itself as a set of novel, concentration dependent, dual action agonists/antagonists for the T-type calcium channel.     

Enhancer and competitive allosteric modulation model for G-protein-coupled receptors

A new mathematical model, referred to as Enhancer and Competitive Allosteric Modulator (ECAM) model, developed with the aim of quantitatively describing the interaction of an allosteric modulator with both enhancer and competitive properties towards G-protein-coupled receptors is described here. Model simulations for equilibrium (displacement-like and saturation-like), and kinetic (association and dissociation) binding experiments were performed. The results showed the ability of the model to interpret a number of possible ligand-receptor binding behaviors. In particular, the binding properties of PD81723, an enhancer and competitive allosteric modulator for the adenosine A₁ receptor, were experimentally evaluated by radioligand binding assays and interpreted by the ECAM model. The results also offer a theoretical background enabling the design and optimization of compounds endowed with allosteric enhancer, competitive, agonist, antagonist, and inverse agonist properties.     

Discovery and expanded SAR of 4,4-disubstituted quinazolin-2-ones as potent T-type calcium channel antagonists

The discovery and synthesis of 4,4-disubstituted quinazolinones as T-type calcium channel antagonists is reported. Based on lead compounds 2 and 3, a focused SAR campaign driven by the optimization of potency, metabolic stability, and pharmacokinetic profile identified 45 as a potent T-type Ca²⁺ channel antagonist with minimized PXR activation. In vivo, 45 suppressed seizure frequency in a rat model of absence epilepsy and showed significant alterations of sleep architecture after oral dosing to rats as measured by EEG.     

Block of T-type Ca channels in guinea pig atrial cells by antiarrhythmic agents and Ca channel antagonists

Myocardial cells have two types of Ca channels commonly called T-type and L-type. Whole cell Ca channel currents in guinea pig atrial myocytes can be separated and quantitated by analyzing channel closing kinetics after a brief depolarization (tail current analysis). L-type Ca channels deactivate rapidly when the membrane is repolarized and T-type Ca channels deactivate relatively slowly. Ca channel block by the therapeutically useful Ca channel antagonists is voltage dependent, so it is desirable to study block of both channel types over an extended voltage range. Tail current analysis allows this and was used to study block of both types of Ca channels under identical conditions. Amiodarone, bepridil, and cinnarizine block T-type Ca channels more potently than L-type Ca channels when binding equilibrates at normal diastolic potentials (approximately -90 mV). None of these drugs is a selective blocker of T-type Ca channels because block of L-type Ca channels is enhanced when cells are almost completely depolarized. Although weak block of T-type Ca channels by 1,4-dihydropyridines has usually been reported, we found that felodipine blocks these channels with high affinity. When most T-type Ca channels are inactivated, the apparent dissociation constant (KI) is 13 nM. Felodipine also blocks T-type Ca channels in GH3 cells (a cell line derived from rat anterior pituitary), but KI = 700 nM. Thus, T-type Ca channels in different cell types are pharmacologically distinct. Felodipine can block L-type Ca channels in atrial cells more potently than T-type Ca channels, but block of L-type Ca channels is potent only at depolarized potentials; block of both channel types is comparable at normal diastolic membrane potentials. Felodipine and the 1,4-dihydropyridines isradipine and (-)-202-791 are approximately equipotent at blocking T-type Ca channels, but differ substantially in potency for block of L-type Ca channels. Block of T-type Ca channels may account for some of the pharmacological effects of 1,4-dihydropyridines and for the antiarrhythmic activity of amiodarone and bepridil.     

"Calcium antagonists": a class of drugs with a bright future. Part II. Determination of basic pharmacological properties

This minireview discusses some simple pharmacological tests useful in detecting biological activity (screening), characterizing mechanisms of action and predicting possible therapeutic applications for calcium antagonists in general and calcium slow channel blockers in particular. In smooth muscle preparations these agents inhibit mechanical effects evoked by K+-depolarization which selectively opens voltage-operated calcium channels (VOC) to allow extracellular Ca++ into the cytosol. In contrast, any inhibition of receptor-mediated responses by calcium antagonists appears to depend on the transduction system and the specific cellular mechanism (e.g. VOC opening consequent to partial depolarization) activated by the receptor and, evidently, on ancillary pharmacological properties of the studied compound. For instance, whereas calcium slow channel blockers antagonize contractions produced by norepinephrine and K+-depolarization in the rat isolated portal vein, they inhibit effectively only the latter response in the rabbit aorta. This apparent discrepancy may be accounted for by the different pool of Ca++ mobilized in the two tissues by norepinephrine. Agents (e.g. diphenylalkylamines, calmodulin blockers) that impair the interaction of Ca++ with intracellular proteins produce effects which are less specific than those of slow channel blockers. Currently, the pharmacological profile of calcium antagonists can be appropriately defined by studying their effects on radioligand (dihydropyridine) binding, radioactive calcium movements through biological membranes, electrophysiological parameters in cardiac and vascular smooth muscle and on various in vivo cardiovascular preparations. Together, these approaches allow a functional classification of new calcium antagonists in relation to already known compounds and some hypotheses on their potential clinical applications. Finally, desirable pharmacokinetics and pharmacological properties for novel calcium antagonists are mentioned. This point will be further explored in the forthcoming minireview which will deal with the clinical applications of calcium antagonists.     

Pharmacological modulation of NMDA receptor activity and the advent of negative and positive allosteric modulators

The NMDA receptor (NMDAR) family of l-glutamate receptors are well known to have diverse roles in CNS function as well as in various neuropathological and psychiatric conditions. Until recently, the types of agents available to pharmacologically regulate NMDAR function have been quite limited in terms of mechanism of action and subtype selectivity. This has changed significantly in the past two years. The purpose of this review is to summarize the many drug classes now available for modulating NMDAR activity. Previously, this included competitive antagonists at the l-glutamate and glycine binding sites, high and low affinity channel blockers, and GluN2B-selective N-terminal domain binding site antagonists. More recently, we and others have identified new classes of NMDAR agents that are either positive or negative allosteric modulators (PAMs and NAMs, respectively). These compounds include the pan potentiator UBP646, the GluN2A-selective potentiator/GluN2C and GluN2D inhibitor UBP512, the GluN2D-selective potentiator UBP551, the GluN2C/GluN2D-selective potentiator CIQ as well as the new NMDAR-NAMs such as the pan-inhibitor UBP618, the GluN2C/GluN2D-selective inhibitor QZN46 and the GluN2A inhibitors UBP608 and TCN201. These new agents do not bind within the l-glutamate or glycine binding sites, the ion channel pore or the N-terminal regulatory domain. Collectively, these new allosteric modulators appear to be acting at multiple novel sites on the NMDAR complex. Importantly, these agents display improved subtype-selectivity and as NMDAR PAMs and NAMs, they represent a new generation of potential NMDAR therapeutics.     

Design, synthesis, and biological evaluation of novel T-Type calcium channel antagonists

This paper describes the synthesis of several novel T-type calcium channel antagonists that inhibit calcium influx into the cell, which in turn regulates unknown aspects of the cell cycle pathway that are responsible for cellular proliferation. A library of compounds was synthesized and a brief structure activity relationship will be described. From these studies we have identified a compound (1) that displays anti-proliferative activity in the low micromolar range across a variety of cancer cell lines.     

Calcium channels: evidence for oligomeric nature by target size analysis.

Radiation inactivation was employed to measure the molecular size of calcium channels in guinea-pig skeletal muscle membranes, labelled by the potent 1,4-dihydropyridine calcium antagonist [3H]nimodipine. The molecular size was decreased when the membranes were preincubated and assayed with d-cis-diltiazem, a calcium channel blocker, which is structurally unrelated to the 1,4-dihydropyridines. d-cis-Diltiazem, which is a positive heterotropic regulator of 1,4-dihydropyridine calcium channel binding in vitro, reduced the molecular size from 178 000 to 111 500. 1-cis-Diltiazem, the diastereoisomer, which is devoid of calcium antagonistic action, did not decrease the molecular size of the 1,4-dihydropyridine binding site. Neither diastereoisomer affected the molecular size of the membrane-bound acetyl-cholinesterase, indicating that a stereospecific interaction with the calcium channel structure is the basis for these observations. It is concluded that this decrease in size is indicative of the oligomeric nature of the calcium channel and that calcium channel blockers, acting via different, but interacting drug receptor sites, induce different conformations of the channel structure, resulting in altered conductivity for ions.     

T-type calcium channels and tumor proliferation

The role of T-type Ca2+ channels in proliferation of tumor cells is reviewed. Intracellular Ca2+ is important in controlling proliferation as evidenced by pulses, or oscillations, of intracellular Ca2+ which occur in a cell cycle-dependent manner in many tumor cells. Voltage-gated calcium channels, such as the T-type Ca2+ channel, are well suited to participate in such oscillations due to their unique activation/inactivation properties. Expression of the T-type Ca2+ channels has been reported in numerous types of tumors, and has been shown to be cell cycle-dependent. Overexpression of the alpha1 subunit of T-type Ca2+ channels in human astrocytoma, neuroblastoma and renal tumor cell lines enhanced proliferation of these cells. In contrast, targeting of the alpha1 subunit of the T-type calcium channel via siRNA decreased proliferation of these cells. A Ca2+ oscillatory model is proposed involving potassium channels, Ca2+ stores and Ca2+ exchangers/transporters. A review of T-type channel blockers is presented, with a focus on mibefradil-induced inhibition of proliferation. The development of newer blockers with higher selectivity and less potential side effects are discussed. The conclusion reached is that calcium channel blockers serve as a potential therapeutic approach for tumors whose proliferation depends on T-type calcium channel expression.     

A role for voltage gated T-type calcium channels in mediating "capacitative" calcium entry?

Calcium entry through plasma membrane calcium channels is one of the most important cell signaling mechanism involved in such diverse functions as secretion, contraction and cell growth by regulating gene expression, proliferation and apoptosis. The identity of plasma membrane calcium channels, the main regulators of calcium entry, involved in cell proliferation has been thus extensively sought. Among these, a calcium entry pathway called capacitative calcium entry (CCE), activated by calcium store depletion, is particularly important in non-excitable cells. Though this capacitative calcium entry is generally supposed to occur through TRP channels there is some evidence that voltage-dependent T-type calcium channels may contribute to calcium entry after store depletion. Here we show that though mibefradil, a T-type calcium channel blocker, is able to reduce capacitative calcium entry induced by either thapsigargin or ATP, this was not mimicked by any other T-type calcium channel inhibitors even in cells overexpressing alpha(1H) T-type calcium channels, leading us to conclude that T-type calcium channels are not responsible for the capacitative calcium entry observed in different cancer cell lines. On the contrary, we show that the action of mibefradil on capacitative calcium entry is due to an action on store-operated calcium channels.     

A Cav3.2/Stac1 molecular complex controls T-type channel expression at the plasma membrane

Low-voltage-activated T-type calcium channels are essential contributors to neuronal physiology where they play complex yet fundamentally important roles in shaping intrinsic excitability of nerve cells and neurotransmission. Aberrant neuronal excitability caused by alteration of T-type channel expression has been linked to a number of neuronal disorders including epilepsy, sleep disturbance, autism, and painful chronic neuropathy. Hence, there is increased interest in identifying the cellular mechanisms and actors that underlie the trafficking of T-type channels in normal and pathological conditions. In the present study, we assessed the ability of Stac adaptor proteins to associate with and modulate surface expression of T-type channels. We report the existence of a Ca_v3.2/Stac1 molecular complex that relies on the binding of Stac1 to the amino-terminal region of the channel. This interaction potently modulates expression of the channel protein at the cell surface resulting in an increased T-type conductance. Altogether, our data establish Stac1 as an important modulator of T-type channel expression and provide new insights into the molecular mechanisms underlying the trafficking of T-type channels to the plasma membrane.