Enantiomer selectivity and the development of tolerance to the behavioral effects of the calcium channel activator BAY K 8644

Lymphatic-draining nanoparticles deliver Bay K8644 payload to lymphatic vessels and enhance their pumping function

Dysfunction of collecting lymphatic vessel pumping is associated with an array of pathologies. S-(-)-Bay K8644 (BayK), a small-molecule agonist of L-type calcium channels, improves vessel contractility ex vivo but has been left unexplored in vivo because of poor lymphatic access and risk of deleterious off-target effects. When formulated within lymph-draining nanoparticles (NPs), BayK acutely improved lymphatic vessel function, effects not seen from treatment with BayK in its free form. By preventing rapid drug access to the circulation, NP formulation also reduced BayK's dose-limiting side effects. When applied to a mouse model of lymphedema, treatment with BayK formulated in lymph-draining NPs, but not free BayK, improved pumping pressure generated by intact lymphatic vessels and tissue remodeling associated with the pathology. This work reveals the utility of a lymph-targeting NP platform to pharmacologically enhance lymphatic pumping in vivo and highlights a promising approach to treating lymphatic dysfunction.

The enantiomer pair of 24S- and 24R-hydroxycholesterol differentially alter activity of large-conductance Ca2+ -dependent K+ (slo1 BK) channel

24S-hydroxycholesterol (HC) is most abundant oxysterols in the brain, passes through blood brain barrier, and is therefore regarded as an intermediary for brain cholesterol elimination. We reported that large-conductance Ca²⁺ - and voltage-activated K⁺ (slo1 BK) channels are suppressed by this oxysterol, which is presumably intercalated into cell membrane to access the outer surface of the channel. Such an outer approach would make it difficult to interact with the inner, ion-conducting part of the channel. The present findings showed that 24R-HC, the racemic counterpart of 24S-HC, also suppressed slo1 BK channel but in a different voltage-dependent manner. There was a difference between the effects of the two enantiomers on activation kinetics but not on deactivation kinetics. It is suggested that the chirality contributes to the efficacy of channel blockers that act from outer lipophilic parts of channels, as with those which act on the inner, ion-permeable surface.

Analgesic effects of amiodarone in mouse models of pain

Purpose: Although amiodarone is classified as a Vaughan-Williams class Ⅲ antiarrhythmic drug, it has inhibitory effects on voltage-gated sodium and calcium channels and on β-adrenergic receptors. Given these pharmacological profiles, amiodarone may have analgesic properties. Most patients who are prescribed amiodarone possess multiple cardiovascular risk factors. Despite the fact that pain plays a crucial role as a clinical indicator of cardiovascular events, the effects of amiodarone on pain have not been investigated. The aim of the current study was to investigate the analgesic effects of amiodarone by using mouse models of pain in an effort to elucidate underlying mechanisms. Methods: Adult male C57B6 mice received single bolus intraperitoneal injections of amiodarone at doses of 25, 50, 100, and 200 mg/kg, while the mice in the control group received only normal saline. The analgesic effects of amiodarone were evaluated using the acetic acid-induced writhing test, formalin test, and tail withdrawal test. In addition, the potassium channel opener NS1643, voltage-gated sodium channel opener veratrine, calcium channel opener BAYK8644, and selective β-adrenergic agonist isoproterenol were used to uncover the underlying mechanism. Results: During the acetic acid-induced writhing test, formalin test, and tail withdrawal test, amiodarone induced analgesic responses in a dose-dependent manner. The analgesic effects of amiodarone were abolished by veratrine but not by NS1643, BAYK8644, or isoproterenol. Conclusion: Amiodarone induced analgesic responses in a dose-dependent manner, likely by blocking voltage-gated sodium channels. These results indicate that clinical doses of amiodarone can affect nociception and may mask or attenuate pain induced by acute cardiovascular events.

Discovery of 'molecular switches' within a GIRK activator scaffold that afford selective GIRK inhibitors

This letter describes a multi-dimensional SAR campaign based on a potent, efficacious and selective GIRK1/2 activator (~10-fold versus GIRK1/4 and inactive on nonGIRK 1-containing GIRKs, GIRK 2 or GIRK2/3). Further chemical optimization through an iterative parallel synthesis effort identified multiple 'molecular switches' that modulated the mode of pharmacology from activator to inhibitor, as well as engendering varying selectivity profiles for GIRK1/2 and GIRK1/4. Importantly, these compounds were all inactive on nonGIRK1 containing GIRK channels. However, SAR was challenging as subtle structural modifications had large effects on both mode of pharmacology and GIRK1/2 and GIRK1/4 channel selectivity.

Expression of voltage-gated calcium channel subunit alpha1C in epidermal keratinocytes and effects of agonist and antagonists of the channel on skin barrier homeostasis

Recent studies demonstrated that skin surface electric conditions affect epidermal permeability barrier homeostasis. These results suggest the existence of voltage sensor on the keratinocytes of the epidermis. On the contrary, specific blockers of the voltage-gated calcium channel (VGCC) also affect epidermal barrier homeostasis, but the existence and function of the channel has not been determined. We demonstrated here immunohistochemically the expression of the main subunit of the L-type VGCC, alpha1C, which alone has a calcium channel function, in mouse and human epidermis. Immunostaining, RT-PCR, and Western blotting were carried out to detect the channel protein. Messenger RNA of alpha1C was also detected in mouse epidermis and human keratinocyte culture by RT-PCR. We also evaluated the function of the channel in the cultured human keratinocytes. Previously, we demonstrated that influx of calcium ion into epidermal keratinocytes delayed the barrier recovery after barrier disruption and topical application of calcium channel blocker accelerated the barrier recovery. In this study, topical application of nifedipine and R-(+)-BAY K8644 after tape stripping of hairless mice accelerated the barrier repair rate while application of S-(-)-BAY K8644 delayed the barrier recovery. These results suggest that the VGCC exists on epidermal keratinocytes and plays an important role in skin barrier homeostasis.

Calcium channel agonists and dystonia in the mouse

Systemic administration of the L-type calcium channel agonists +/-Bay K 8644 or FPL 64176 causes a characteristic pattern of motor dysfunction in normal C57BL/6J mice that resembles generalized dystonia. There is no associated change in the electroencephalogram, confirming that the motor disorder does not reflect epileptic seizures. However, the electromyogram reveals an increase in baseline motor unit activity with prolonged phasic discharges consistent with dystonia. The duration and severity of dystonia is dependent on the dose administered and the age of the animal at testing. The effects are transient, with the return of normal motor behavior 1-4 hours after treatment. Similar effects can be provoked by intracerebral administration of small amounts of the drugs, indicating a centrally mediated response. Dystonia can be attenuated by co-administration of dihydropyridine L-type calcium channel antagonists (nifedipine, nimodipine, and nitrendipine) but not by non-dihydropyridine antagonists (diltiazem, verapamil, and flunarizine). These results implicate abnormal function of L-type calcium channels in the expression of dystonia in this model.

Calcium channel activation and self-biting in mice

The L type calcium channel agonist (+/-)Bay K 8644 has been reported to cause characteristic motor abnormalities in adult mice. The current study shows that administration of this drug can also cause the unusual phenomenon of self-injurious biting, particularly when given to young mice. Self-biting is provoked by injecting small quantities of (+/-)Bay K 8644 directly into the lateral ventricle of the brain, suggesting a central effect of the drug. Similar behaviors can be provoked by administration of another L type calcium channel agonist, FPL 64176. The self-biting provoked by (+/-)Bay K 8644 can be inhibited by pretreating the mice with dihydropyridine L type calcium channel antagonists such as nifedipine, nimodipine, or nitrendipine. However, self-biting is not inhibited by nondihydropyridine antagonists including diltiazem, flunarizine, or verapamil. The known actions of (+/-)Bay K 8644 as an L type calcium channel agonist, the reproduction of similar behavior with another L type calcium channel agonist, and the protection afforded by certain L type calcium channel antagonists implicate calcium channels in the mediation of the self-biting behavior. This phenomenon provides a model for studying the neurobiology of this unusual behavior.

Effects of dihydropyridine Ca2+ channel blockers on the discriminative stimulus and the motor impairing effects of (+/-)-Bay K 8644

Functional interactions between the dihydropyridine Ca2+ channel activator, (+/-)-Bay K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyphenyl )-pyridine-5-carboxylate), and several dihydropyridine L-type Ca2+ channel blockers were investigated on rotarod performance in mice and in rats trained to discriminate between (+/-)Bay K 8644 and saline. When administered alone, (+/-)-Bay K 8644 produced dose-dependent impairments of rotarod activity with an ED50 of 1.3 mg/kg. Pretreatment with nifedipine (10-30 mg/kg) produced dose-dependent rightward shifts of the (+/-)-Bay K 8644 dose-response curve. In contrast, pretreatment with several other dihydropyridine L-type Ca2+ channel blockers, including nicardipine, nimodipine, isradipine and nitrendipine, did not modify the (+/-)-Bay K 8644 dose-effect function. Rats learned to discriminate between (+/-)-Bay K 8644 (0.5 mg/kg) and saline in an average of 65 training sessions. In substitution tests, the Ca2+ channel activator engendered dose-related increases in the percentage of rats selecting the drug-associated lever with an ED50 of 0.19 mg/kg. Pretreatment with nifedipine (10 mg/kg) produced a rightward shift of the (+/-)-Bay K 8644 dose-response function. Pretreatment with nicardipine (2.5 mg/kg) only partially antagonised the training dose of (+/-)-Bay K 8644 whereas nimodipine (0.6-10 mg/kg) did not affect the (+/-)-Bay K 8644 discriminative stimulus. The results of the present study show that the behavioural effects of the dihydropyridine Ca2+ channel activator are differentially modified by dihydropyridine L-type Ca2+ channel blockers. These results may suggest that dihydropyridine blockers possess different intrinsic activities or act at different binding sites.

The effects of chronic treatment with the dihydropyridine, Bay K 8644, on hyperexcitability due to ethanol withdrawal, in vivo and in vitro

1. The effects of chronic treatment with the dihydropyridine, Bay K 8644, were studied on the ethanol withdrawal syndrome, in vivo and in vitro. 2. Addition of racemic Bay K 8644 to the drinking mixture, throughout the chronic ethanol treatment, decreased the behavioural excitability seen during ethanol withdrawal in vivo. 3. All the signs of hyperexcitability in field potentials in the isolated hippocampal slice, caused by ethanol withdrawal, were decreased by the chronic administration of Bay K 8644. 4. These effects resembled those previously reported for chronic administration of calcium channel antagonists; racemic Bay K 8644 has both calcium channel activating and antagonist properties. 5. Measurement of brain levels of Bay K 8644 at the end of the chronic treatment showed that the compound reached micromolar concentrations during the treatment, but none could be detected in the tissues at the time of the above measurements. 6. It is possible that the results might be explained by predominance of the calcium channel antagonist properties of this compound, owing to the high central concentrations achieved during the treatment. Tolerance to the calcium channel activating properties of Bay K 8644 may also have occurred during the chronic treatment.

The effects of dihydropyridine calcium channel modulators on pentylenetetrazole convulsions

The effects of low doses of dihydropyridine (DHP) calcium channel antagonists nimodipine, nifedipine, (-)-R-202-791, and amlodipine, the DHP calcium channel agonist BAY K 8644 were investigated on clonic convulsions to pentylenetetrazole (PTZ) in mice. Nimodipine (2-20 mg/kg) produced a dose-dependent increase in the onset time for convulsions, but did not decrease the number of mice convulsing. Nifedipine, amlodipine (10 mg/kg) and BAY K 8644 (2 mg/kg) also produced an increase in the onset time for convulsions. (-)-R-202-791 (10 mg/kg) was without effect on clonic convulsions to PTZ. BAY K 8644 increased the number of mice dying from tonic-extension convulsions to PTZ. Nimodipine did not affect convulsions elicited by strychnine. Thus, low doses of DHP calcium antagonists possess anticonvulsant properties which are structurally dependent, while DHP calcium channel activators may act to promote convulsions. These observations suggest and support previous evidence that DHP receptors are important modulatory sites for the convulsive state.