Aconitine-induced increase and decrease of acetylcholine release in the mouse phrenic nerve-hemidiaphragm muscle preparation

Construction of the highly oxidized bicyclo[3.2.1]octane CD ring system of aconitine via a late stage enyne cycloisomerization

An enyne cycloisomerization enables assembly of the highly oxidized bicyclo[3.2.1]octane CD rings of the complex diterpenoid alkaloid aconitine.

Calcium antagonists cause dry mouth by inhibiting resting saliva secretion

Ca2+ antagonists cause dry mouth by inhibiting saliva secretion. The present study was undertaken to elucidate the mechanism by which Ca2+ antagonists cause dry mouth. Since the intracellular Ca2+ concentration ([Ca2+]i) is closely related to saliva secretion, [Ca2+]i was measured with a video-imaging analysis system by using human submandibular gland (HSG) cells as the material. The Ca2+ antagonist, nifedipine, inhibited the elevation in [Ca2+]i induced by 1-10 microM carbachol (CCh), but had no inhibitory effect on that induced by 30 and 100 microM CCh. The other kinds of Ca2+ antagonists, verapamil (10 microM), diltiazem (10 microM), and the inorganic Ca2+ channel blocker, CdCl2 (50 microM), also inhibited the [Ca2+]i elevation induced by 10 microM CCh. The Ca2+ channel activator, Bay K 8644 (5 microM), significantly enhanced the CCh (10 microM)-induced [Ca2+]i elevation. Endothelin-1 and norepinephrine also increased the CCh (10 microM)-induced [Ca2+]i elevation. SKF-96365 reversed the enhancement of the CCh (10 microM)-induced [Ca2+]i elevation caused by AlF4- and phenylephrine. The phospholipase Cbeta (PLCbeta) inhibitor, U-73122 (5 microM), significantly inhibited the [Ca2+]i elevation induced by 100 microM CCh compared with that induced by 10 microM CCh, while the PLCbeta activator, m-3M3FBS (20 microM), significantly increased the [Ca2+]i elevation induced by 100 microM CCh compared with that induced by 10 microM CCh. We therefore conclude that non-selective cation and voltage-dependent Ca2+ channels are involved in resting salivation and that Ca2+ antagonists depress H2O secretion by blocking the Ca2+ channels and thereby cause dry mouth.

Medical benefits of using natural compounds and their derivatives having multiple pharmacological actions

The multiple pharmacological actions of a unique compound are a prerequisite for classifying drugs as highly efficacious, because the multiple pharmacological actions offer the possibility of treating various symptoms of chronic diseases as described below. 1) Sustained hyperglycemia induces macrovascular and microvascular complications in type 2 diabetes mellitus. Antihyperglycemic medication and the control of postprandial hyperglycemia are essentially important for normalizing plasma glucose level. Gymnemic acid IV isolated from Gymnema sylvestre (Asclepiadaceae) leaves has antisweet, antihyperglycemic, glucose uptake inhibitory, and gut glycosidase inhibitory effects. Most of these pharmacological effects may synergistically contribute to alleviating type 2 diabetes-related symptoms. 2) Diabetic skeletal and vascular smooth muscles are hypersensitive to chemical transmitters, cytokines and autacoids. The sensitivity of neuromuscular synapses is enhanced in diabetes, which seems to be closely associated with neuropathy as one of the diabetic complications. beta-Eudesmol found in Atractylodes lancea rhizome has a desensitizing channel blocking action to nicotinic acetylcholine receptors, anti-angiogenic action in vascular endothelium, and neuronal differentiation actions. These multiple pharmacological actions are favorable for treating angiogenic diseases possibly including the complications of diabetes, namely, retinopathy and nephropathy, and cancer. 3) Nipradilol is clinically utilized as a topical antiglaucoma drug. The ocular hypotensive effects of this compound are brought about by its alpha1 and beta-adrenergic receptor blocking actions, and nitric oxide (NO) releasing action. NO directly activates cyclooxygenases. All these pharmacologic effects are beneficial for treating glaucoma. The selectivity and specificity of drug action are required for treating acute diseases, infections or for acting as useful reagents. The pleiotropic actions of natural compounds and their derivatives serve as important clues for developing new drugs for various chronic diseases.

Aconitine facilitates spontaneous transmitter release at rat ventromedial hypothalamic neurons

The effects of aconitine, an Aconitum alkaloid, on spontaneous inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs respectively) were investigated in the mechanically dissociated rat ventromedial hypothalamic (VMH) neurons in which native presynaptic nerve terminals remained intact. Under current-clamp conditions, aconitine (3 x 10(-6) M) depolarized the neuron with generating the action potentials. The aconitine-induced depolarization was markedly suppressed in the presence of CNQX but it was facilitated in the presence of bicuculline, suggesting that release of excitatory and inhibitory neurotransmitters may be involved in the aconitine action in addition to its direct action on postsynaptic membrane. Under the voltage-clamp conditions, aconitine reversibly increased the frequency of spontaneous IPSC and EPSC frequency, but it did not alter their amplitude distribution. Tetrodotoxin (TTX, 3 x 10(-7) M) completely abolished the aconitine action on spontaneous IPSC frequency. Likewise removal of extracellular Na(+) completely suppressed the aconitine action. Both Ca(2+)-free external solution or addition of 10(-4) M Cd(2+) to normal solutions eliminated the facilitatory effect of aconitine on the IPSC frequency. Overall these results suggest that aconitine depolarizes the presynaptic membrane by activating voltage-dependent Na(+) channels. Increase of intraterminal Ca(2+) concentration via an activation of voltage-dependent Ca(2+) channels in turn enhances the spontaneous transmitter release from presynaptic nerve terminals. The presynaptic action of aconitine may play a crucial role for membrane excitability of rat VMH neurons.

Counter effects of higenamine and coryneine, components of aconite root, on acetylcholine release from motor nerve terminal in mice

The counter effects of higenamine and coryneine, components of aconite root, on acetylcholine (ACh) release from motor nerve terminals in the mouse phrenic nerve-diaphragm muscle preparation were studied by a radioisotope method. Both nerve-evoked release and spontaneous release of [3H]-ACh from the preparation preloaded with [3H]-choline were measured. The change in the tetanic tension of muscle was simultaneously recorded in the same preparation. Higenamine (10 microM) augmented both the nerve-evoked and spontaneous ACh releases, and the muscle tension. The effects were inhibited by pretreatment with propranolol (10 microM), a beta-adrenoceptor antagonist. Coryneine reduced the nerve-evoked release of ACh, accelerated the decay of tetanic tension (tetanic fade) at 30 microM, and it depressed the peak amplitude of tetanic tension at a higher concentration of 100 microM. These results suggest that of the two components contained in aconite root, higenamine increases ACh release via activation of beta-adrenoceptor, and conversely coryneine depresses ACh release by preferentially acting at motor nerve terminal.

Effects of aconitine on neurotransmitter release in the rat neuromuscular junction

Aconitine (ACO), A Na+ channel activator, induces depolarization in skeletal muscle and blocks neuromuscular transmission. We investigated the effects of ACO on neurotransmitter release in the rat isolated phrenic nerve-diaphragm preparation at 24 +/- 1 degrees C. ACO inhibited the twitch responses to nerve stimulation but did not affect direct muscle contractions. ACO, without causing excessive membrane depolarization, increased the frequency of miniature end-plate potential (MEPP)s, but did not alter their amplitude or time course. The increase in MEPP frequency started about 60, 30 and 15 min after the application of 6, 20 and 60 microM ACO, respectively. MEPP frequency reached its maximum (250-400 sec-1), within 10-15 min after it began to increase. ACO, without altering direct muscle action potentials decreased the amplitude and blocked end-plate potential (EPP)s and nerve action potential (NAP)s simultaneously, before the increase in MEPP frequency became evident. ACO did not increase MEPP frequency in Ca(2+)-free media. Prior application of tetrodotoxin (1 microM) inhibited the ACO-induced MEPP frequency increase. Carbamazepine (120 microM) and amiloride (100 microM) did not completely inhibit the MEPP frequency increase but prolonged the latency. ACO-induced alterations in the neuromuscular transmission exhibited minimal recovery upon washing for 2-3 hr. These results indicate that ACO-induced neuromuscular blockade is mainly due to presynaptic mechanisms and can be explained by excessive presynaptic depolarization which leads to the blockade of NAPs and EPPs. Depolarization in turn increases intraterminal Ca2+ concentration and results in an excessive increase in MEPP frequency.