Inhibition of human recombinant T-type calcium channels by the endocannabinoid N-arachidonoyl dopamine.

BACKGROUND AND PURPOSE: N-arachidonoyl dopamine (NADA) has complex effects on nociception mediated via cannabinoid CB(1) receptors and the transient receptor potential vanilloid receptor 1 (TRPV1). Anandamide, the prototypic CB(1)/TRPV1 agonist, also inhibits T-type voltage-gated calcium channel currents (I(Ca)). These channels are expressed by many excitable cells, including neurons involved in pain detection and processing. We sought to determine whether NADA and the prototypic arachidonoyl amino acid, N-arachidonoyl glycine (NAGly) modulate T-type I(Ca) EXPERIMENTAL APPROACH: Human recombinant T-type I(Ca) (Ca(V)3 channels) expressed in HEK 293 cells and native mouse T-type I(Ca) were examined using standard whole-cell voltage clamp electrophysiology techniques. KEY RESULTS: N-arachidonoyl dopamine completely inhibited Ca(V)3 channels with a rank order of potency (pEC(50)) of Ca(V)3.3 (6.45) > or = Ca(V)3.1 (6.29) > Ca(V)3.2 (5.95). NAGly (10 micromol.L(-1)) inhibited Ca(V)3 I(Ca) by approximately 50% or less. The effects of NADA and NAGly were voltage- but not use-dependent, and both compounds produced significant hyperpolarizing shifts in Ca(V)3 channel steady-state inactivation relationships. By contrast with anandamide, NADA and NAGly had modest effects on Ca(V)3 channel kinetics. Both NAGly and NADA inhibited native T-type I(Ca) in mouse sensory neurons. CONCLUSIONS AND IMPLICATIONS: N-arachidonoyl dopamine and NAGly increase the steady-state inactivation of Ca(V)3 channels, reducing the number of channels available to open during depolarization. These effects occur at NADA concentrations at or below to those affecting CB(1) and TRPV1 receptors. Together with anandamide, the arachidonoyl neurotransmitter amides, NADA and NAGly, represent a new family of endogenous T-type I(Ca) modulators.

Inhibition of recombinant human T-type calcium channels by Delta9-tetrahydrocannabinol and cannabidiol.

Delta(9)-Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the most prevalent biologically active constituents of Cannabis sativa. THC is the prototypic cannabinoid CB1 receptor agonist and is psychoactive and analgesic. CBD is also analgesic, but it is not a CB1 receptor agonist. Low voltage-activated T-type calcium channels, encoded by the Ca(V)3 gene family, regulate the excitability of many cells, including neurons involved in nociceptive processing. We examined the effects of THC and CBD on human Ca(V)3 channels stably expressed in human embryonic kidney 293 cells and T-type channels in mouse sensory neurons using whole-cell, patch clamp recordings. At moderately hyperpolarized potentials, THC and CBD inhibited peak Ca(V)3.1 and Ca(V)3.2 currents with IC(50) values of approximately 1 mum but were less potent on Ca(V)3.3 channels. THC and CBD inhibited sensory neuron T-type channels by about 45% at 1 mum. However, in recordings made from a holding potential of -70 mV, 100 nm THC or CBD inhibited more than 50% of the peak Ca(V)3.1 current. THC and CBD produced a significant hyperpolarizing shift in the steady state inactivation potentials for each of the Ca(V)3 channels, which accounts for inhibition of channel currents. Additionally, THC caused a modest hyperpolarizing shift in the activation of Ca(V)3.1 and Ca(V)3.2. THC but not CBD slowed Ca(V)3.1 and Ca(V)3.2 deactivation and inactivation kinetics. Thus, THC and CBD inhibit Ca(V)3 channels at pharmacologically relevant concentrations. However, THC, but not CBD, may also increase the amount of calcium entry following T-type channel activation by stabilizing open states of the channel.

Synthesis and structure-activity relationships of thiadiazole-derivatives as potent and orally active peroxisome proliferator-activated receptors alpha/delta dual agonists.

Replacement of the methyl-thiazole moiety of GW501516 (a PPARdelta selective agonist) with [1,2,4]thiadiazole gave compound 21 which unexpectedly displayed submicromolar potency as a partial agonist at PPARalpha in addition to the high potency at PPARdelta. A structure-activity relationships study of 21 resulted in the identification of 40 as a potent and selective PPARalpha/delta dual agonist. Compound 40 and its close analogs represent a new series of PPARalpha/delta dual agonists. The high potency, high selectivity, significant gene induction, excellent PK profiles, low P450 inhibition or induction, and good in vivo efficacy in four animal models support 40 being selected as a pre-clinical study candidate, and may render 40 as a valuable pharmacological tool in elucidating the complex roles of PPARalpha/delta dual agonists, and the potential usage for the treatment of metabolic syndrome.

Methanandamide activation of a novel current in mouse trigeminal ganglion sensory neurons in vitro.

Anandamide is an endogenous agonist for cannabinoid receptors and produces analgesia by acting at these receptors in several sites in the brain and peripheral nervous system. Anandamide is also an agonist at the TRPV1 receptor, a protein that serves as an important integrator of noxious stimuli in sensory neurons. Although anandamide actions at CB1 and TRPV1 receptors can explain many of its effects on sensory neurons, some apparently CB1- and TRPV1-independent effects of anandamide have been reported. To explore possible mechanisms underlying these effects we examined the actions of the stable anandamide analog methanandamide on the membrane properties of trigeminal ganglion neurons from mice with TRPV1 deleted. We found that methanandamide and anandamide activate a novel current in a subpopulation of small trigeminal ganglion neurons. Methanandamide activated the current (EC(50) 2 microM) more potently than it activates TRPV1 under the same conditions. The methanandamide-activated current reverses at 0 mV and does not inactivate at positive potentials but declines rapidly at negative membrane potentials. Activation of the current is not mediated via cannabinoid receptors and does not appear to involve G proteins. The phytocannabinoid Delta(9)-tetrahydrocannabinol, the endocannabinoid-related molecules N-arachidonoyl dopamine and N-arachidonoyl glycine and the non-specific TRPV channel activator 2-aminoethoxydiphenyl borate do not mimic the effects of methanandamide. The molecular identity of the current remains to be established, but we have identified a potential new effector for endocannabinoids in sensory neurons, and activation of this current may underlie some of the previously reported CB1 and TRPV1-independent effects of these compounds.

Synthesis and identification of [1,2,4]thiadiazole derivatives as a new series of potent and orally active dual agonists of peroxisome proliferator-activated receptors alpha and delta.

Cardiovascular disease is the most common cause of morbidity and mortality in developed nations. To effectively target dyslipidemia to reduce the risk of cardiovascular disease, it may be beneficial to activate the peroxisome proliferator-activated receptors (PPARs) PPARalpha and PPARdelta simultaneously through a single molecule. Replacement of the methylthiazole of 5 (the PPARdelta selective agonist) with [1,2,4]thiadiazole gave compound 13, which unexpectedly displayed submicromolar potency as a partial agonist at PPARalpha in addition to the high potency at PPARdelta. Optimization of 13 led to the identification of 24 as a potent and selective PPARalpha/delta dual agonist. Compound 24 and its close analogs represent a new series of PPARalpha/delta dual agonists. The high potency, significant gene induction, excellent PK profiles, and good in vivo efficacies in three animal models may render compound 24 as a valuable pharmacological tool in elucidating the complex roles of PPARalpha/delta dual agonists and as a potential treatment of the metabolic syndrome.

GABAergic mechanisms involved in the vagally mediated heart rate response to muscle contraction as revealed by studies with benzodiazepines.

The aim of this study was to determine if central GABA mechanisms are involved in the cardiac vagal withdrawal at the beginning of exercise in man. We tested whether GABA-enhancing effects of a benzodiazepine could be observed in the HR change (R-R interval) immediately following the onset of a brief (10s) isometric contraction (60 % maximum) of the biceps muscle. The difference between the change in R-R interval occurring during the same phase of respiration was compared for placebo (Pla) and 10 mg oral diazepam (Dz) treatment in a double blind, crossover trial. ECG, blood pressure, respiration and biceps muscle tension were recorded. The subjects breathed to a metronome and R-R interval measurements were plotted for early and late inspiration and early and late expiration. The mean values of the first late expiration R-R interval immediately following the start of contraction in early expiration were compared to the same measurements without contraction. Contractions initiated following diazepam treatment resulted in a significantly greater reduction in R-R interval (P < 0.05) implying that GABAergic suppression of cardiac vagal outflow may be responsible for contraction-induced tachycardia in man.

Nitric oxide and cardiac parasympathetic control in human heart failure.

Cardiac parasympathetic control has prognostic significance in heart failure, but the control mechanisms of this system remain poorly defined. We have demonstrated previously a facilitatory role for nitric oxide (NO) in the parasympathetic control of heart rate in young healthy human subjects. In view of the complex abnormalities of regional NO activity observed in chronic heart failure, we now aim to establish if this mechanism is active in subjects with this condition. Groups of 12 heart failure patients [NYHA class II-III; mean age 52 years (range 38-67 years)] and 12 age/sex-matched healthy control subjects [mean age 50 years (range 36-62 years)] were studied. Heart rate variability and baroreflex sensitivity were measured during inhibition of endogenous NO production with N(G)-monomethyl-l-arginine (l-NMMA; 3 mg.h(-1).kg(-1)) and during administration of an equipressor dose of the control vasoconstrictor phenylephrine (12-36 microg.h(-1).kg(-1)). Basal levels of nitrate+nitrite were measured in the plasma as an indication of systemic NO production. In the heart failure patients, despite an equal rise in blood pressure with both drugs, high-frequency indices of heart rate variability increased less with l-NMMA than with phenylephrine: RMSSD (root mean square of successive RR-interval differences) increased by 4+/-2 compared with 26+/-8 ms (P<0.001) and high-frequency power increased by 97+/-62 compared with 1372+/-861 ms(2) (P<0.001). The increases in cross-spectral baroreflex sensitivity were also lower with l-NMMA than with phenylephrine [high-frequency alpha-index, 2.2+/-1.3 and 12.6+/-3.8 ms/mmHg respectively (P<0.001); low-frequency alpha-index, 1.3+/-0.9 and 4.3+/-1.7 ms/mmHg respectively (P<0.05)]. Healthy subjects showed a similar discrepancy in the response of high-frequency indices of heart rate variability to the two drugs, although baroreflex sensitivity responses were significantly different only for the high-frequency alpha-index. Levels of plasma nitrate+nitrite were significantly higher in the heart failure patients compared with controls. These data demonstrate that baroreflex-mediated cardiac parasympathetic activation in human heart failure, as in health, is dependent upon endogenous NO synthesis.