Real-World Effectiveness of Ramelteon and Suvorexant for Delirium Prevention in 948 Patients With Delirium Risk Factors.

OBJECTIVE: The aim of this study was to examine the effectiveness of ramelteon and suvorexant for delirium prevention in real-world practice. It explored whether ramelteon and/or suvorexant would affect delirium prevention among both patients at risk for but without delirium (patients at risk) and those with delirium the night before a consultation. METHODS: This multicenter, prospective, observational study was conducted by trained psychiatrists at consultation-liaison psychiatric services from October 1, 2017, to October 7, 2018. Patients who were aged 65 years or older and hospitalized because of acute diseases or elective surgery, had risk factors for delirium, and had insomnia or delirium on the night before the consultation were prescribed ramelteon and/or suvorexant. The decision to take medication was left to the discretion of each patient. The primary outcome was incidence of delirium based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, during the first 7 days. RESULTS: Among 526 patients at risk, those taking ramelteon and/or suvorexant developed delirium significantly less frequently than those who did not, after control for the effects of risk factors on the estimate of an independent association between the effects of ramelteon and/or suvorexant and the outcome of developing delirium (15.7% vs 24.0%; odds ratio [OR] = 0.48;, 95% CI, 0.29-0.80; P = .005). Similar results were found among 422 patients with delirium (39.9% vs 66.3%; OR = 0.36; 95% CI, 0.22-0.59; P < .0001). CONCLUSIONS: Ramelteon and suvorexant appear to be effective for delirium prevention in real-world practice.

An adenosine kinase inhibitor, ABT-702, inhibits spinal nociceptive transmission by adenosine release via equilibrative nucleoside transporters in rat.

Adenosine kinase (AK) inhibitor is a potential candidate for controlling pain, but some AK inhibitors have problems of adverse effects such as motor impairment. ABT-702, a non-nucleoside AK inhibitor, shows analgesic effect in animal models of pain. Here, we investigated the effects of ABT-702 on synaptic transmission via nociceptive and motor reflex pathways in the isolated spinal cord of neonatal rats. The release of adenosine from the spinal cord was measured by HPLC. ABT-702 inhibited slow ventral root potentials (sVRPs) in the nociceptive pathway more potently than monosynaptic reflex potentials (MSRs) in the motor reflex pathway. The inhibitory effects of ABT-702 were mimicked by exogenously applied adenosine, blocked by 8CPT (8-cyclopentyl-1,3-dipropylxanthine), an adenosine A1 receptor antagonist, and augmented by EHNA (erythro-9-(2-hydroxy-3-nonyl) adenine), an adenosine deaminase (ADA) inhibitor. Equilibrative nucleoside transporter (ENT) inhibitors reversed the effects of ABT-702, but not those of adenosine. ABT-702 released adenosine from the spinal cord, an effect that was also reversed by ENT inhibitors. The ABT-702-facilitated release of adenosine by way of ENTs inhibits nociceptive pathways more potently than motor reflex pathways in the spinal cord via activation of A1 receptors. This feature is expected to lead to good analgesic effects, but, caution may be required for the use of AK inhibitors in the case of ADA dysfunction or a combination with ENT inhibitors.

Different mechanisms of extracellular adenosine accumulation by reduction of the external Ca(2+) concentration and inhibition of adenosine metabolism in spinal astrocytes.

Extracellular adenosine is a neuromodulator in the central nervous system. Astrocytes mainly participate in adenosine production, and extracellular adenosine accumulates under physiological and pathophysiological conditions. Inhibition of intracellular adenosine metabolism and reduction of the external Ca(2+) concentration ([Ca(2+)]e) participate in adenosine accumulation, but the precise mechanisms remain unclear. This study investigated the mechanisms underlying extracellular adenosine accumulation in cultured rat spinal astrocytes. The combination of adenosine kinase and deaminase (ADK/ADA) inhibition and a reduced [Ca(2+)]e increased the extracellular adenosine level. ADK/ADA inhibitors increased the level of extracellular adenosine but not of adenine nucleotides, which was suppressed by inhibition of equilibrative nucleoside transporter (ENT) 2. Unlike ADK/ADA inhibition, a reduced [Ca(2+)]e increased the extracellular level not only of adenosine but also of ATP. This adenosine increase was enhanced by ENT2 inhibition, and suppressed by sodium polyoxotungstate (ecto-nucleoside triphosphate diphosphohydrolase inhibitor). Gap junction inhibitors suppressed the increases in adenosine and adenine nucleotide levels by reduction of [Ca(2+)]e. These results indicate that extracellular adenosine accumulation by ADK/ADA inhibition is due to the adenosine release via ENT2, while that by reduction of [Ca(2+)]e is due to breakdown of ATP released via gap junction hemichannels, after which ENT2 incorporates adenosine into the cells.

Neuronal regulation of expression of hydrogen sulfide-producing enzyme cystathionine ß-synthase in rat spinal cord astrocytes.

Cystathionine ß-synthase (CBS), expressed in astrocytes, generates a gaseous neuromodulator, hydrogen sulfide (H2S) in the central nervous system (CNS). However, little is known about the regulatory mechanisms of astrocytic CBS expression and activity. This study evaluated the influence of neurons on astrocytic CBS expression by employing multiple culture systems. Substantial CBS expression was observed in the intact neonatal rat spinal cord, while CBS content was markedly reduced in an astrocyte-enriched culture prepared from the neonatal spinal cord. Immunofluorescence analysis confirmed the localization of spinal cord CBS in astrocytes, but not in neurons. Although CBS expression was weak in the embryonic rat spinal cord, enzyme levels were time-dependently increased in a neuron/astrocyte mixed culture originating from embryonic spinal cord. The reduced CBS expression in isolated neonatal astrocytes was restored by co-culture with embryonic neurons. Together with the observed CBS expression levels, H2S production was relatively low in astrocytes cultured alone, but was considerably higher in astrocytes cultured with neurons. These results indicate that neurons are essential for maintaining the expression and H2S-producing activity of astrocytic CBS in the rat spinal cord.

Contribution of cysteine aminotransferase and mercaptopyruvate sulfurtransferase to hydrogen sulfide production in peripheral neurons.

Hydrogen sulfide (H2 S) is a gaseous neuromodulator produced from L-cysteine. H2 S is generated by three distinct enzymatic pathways mediated by cystathionine γ-lyase (CSE), cystathionine ß-synthase (CBS), and mercaptopyruvate sulfurtransferase (MPST) coupled with cysteine aminotransferase (CAT). This study investigated the relative contributions of these three pathways to H2 S production in PC12 cells (rat pheochromocytoma-derived cells) and the rat dorsal root ganglion. CBS, CAT, and MPST, but not CSE, were expressed in the cells and tissues, and appreciable amounts of H2 S were produced from L-cysteine in the presence of α-ketoglutarate, together with dithiothreitol. The production of H2 S was inhibited by a CAT inhibitor (aminooxyacetic acid), competitive CAT substrates (L-aspartate and oxaloacetate), and RNA interference (RNAi) against MPST. Immunocytochemistry revealed a mitochondrial localization of MPST in PC12 cells and dorsal root ganglion neurons, and the amount of H2 S produced by CAT/MPST at pH 8.0, a physiological mitochondrial matrix pH, was comparable to that produced by CSE and CBS in the liver and the brain, respectively. Furthermore, H2 S production was markedly increased by alkalization. These results indicate that CAT and MPST are primarily responsible for H2 S production in peripheral neurons, and that the regulation of mitochondrial metabolism may influence neuronal H2 S generation. In the peripheral nervous system, hydrogen sulfide (H2 S) has been implicated in neurogenic pain or hyperalgesia. This study provides evidence that H2 S is synthesized in peripheral neurons through two mitochondrial enzymes, cysteine aminotransferase (CAT) and mercaptopyruvate sulfurtransferase (MPST). We propose that mitochondrial metabolism plays key roles in the physiology and pathophysiology of the peripheral nervous system via regulation of neuronal H2 S production.

[Case of optic neuritis associated with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL)].

PURPOSE: To report a case of optic neuritis associated with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). CASE: A 38-year-old woman presented with visual field defects, ocular pain and relative afferent papillary defect (RAPD). Fluorescein angiography demonstrated peripapillary hyperfluorescence of the optic nerve. Optic neuritis was diagnosed soon after. Routine laboratory data were unremarkable. Brain MRI showed a remarkable enhanced region of white matter and abnormal spots in the capsula externa. Multiple sclerosis was outruled by neurological findings and therefore CARASIL was diagnosed according to the criteria. The patient's vision and inflammation of the optic nerve head gradually improved with systemic steroid therapy, but arterial sheathing was observed during the follow-up period. CONCLUSIONS: Clinical manifestations such as optic neuritis and retinal vascular change might be caused by the pathological changes of CARASIL. This is the first report of ophthalmic findings of clinicopathological events of CARASIL.

Voltage-gated channel properties of epithelial cells in porcine vomeronasal organ.

Bipolar vomeronasal sensory neurons (VSNs) in the vomeronasal organ (VNO) are believed to detect pheromones in most mammals. The vomeronasal sensory epithelium (VSE) is composed of VSNs and supporting cells. There are morphological differences in VNOs between species. Many electrophysiological experiments have been performed on rodent VSEs but few on other mammals. We therefore investigated voltage-gated channel properties of cells in the porcine VSE using slice whole-cell voltage-clamp techniques. In immunohistochemical study of the porcine VSE, most PGP9.5-immunoreactive cells were found between the middle and basal region, and negative cells were distributed in the apical to middle region. Depolarizing pulses to epithelial cells from -90mV produced transient inward Na+ channel currents and sustained outward K+ channel currents with various amplitudes. The distribution of cells having high and low Na+ current densities was mostly consistent with the histological distribution of VSNs and supporting cells, respectively. The half-inactivation voltage of voltage-gated Na+ channels in supporting cells was 26mV more negative than that in VSNs. Voltage-gated K+ channel currents in both cell types were suppressed by tetraethylammonium to the same extent. VSNs possessed TTX-sensitive voltage-gated Na+ channels and Ni2+ -sensitive T-type Ca2+ channels. These results suggest that the histological distribution of porcine vomeronasal epithelial cells is more similar to the dog and goat than to rodents, and that the electrophysiological characteristics of porcine vomeronasal epithelial cells are similar to those of rodents. It is also suggested that porcine VSNs detecting pheromones generate action potentials through these channels.

Isoform-specific inhibition of TRPC4 channel by phosphatidylinositol 4,5-bisphosphate.

Full-length transient receptor potential (TRP) cation channel TRPC4alpha and shorter TRPC4beta lacking 84 amino acids in the cytosolic C terminus are expressed in smooth muscle and endothelial cells where they regulate membrane potential and Ca(2+) influx. In common with other "classical" TRPCs, TRPC4 is activated by G(q)/phospholipase C-coupled receptors, but the underlying mechanism remains elusive. Little is also known about any isoform-specific channel regulation. Here we show that TRPC4alpha but not TRPC4beta was strongly inhibited by intracellularly applied phosphatidylinositol 4,5-bisphosphate (PIP(2)). In contrast, several other phosphoinositides (PI), including PI(3,4)P(2), PI(3,5)P(2), and PI(3,4,5)P(3), had no effect or even potentiated TRPC4alpha indicating that PIP(2) inhibits TRPC4alpha in a highly selective manner. We show that PIP(2) binds to the C terminus of TRPC4alpha but not that of TRPC4beta in vitro. Its inhibitory action was dependent on the association of TRPC4alpha with actin cytoskeleton as it was prevented by cytochalasin D treatment or by the deletion of the C-terminal PDZ-binding motif (Thr-Thr-Arg-Leu) that links TRPC4 to F-actin through the sodium-hydrogen exchanger regulatory factor and ezrin. PIP(2) breakdown appears to be a required step in TRPC4alpha channel activation as PIP(2) depletion alone was insufficient for channel opening, which additionally required Ca(2+) and pertussis toxin-sensitive G(i/o) proteins. Thus, TRPC4 channels integrate a variety of G-protein-dependent stimuli, including a PIP(2)/cytoskeleton dependence reminiscent of the TRPC4-like muscarinic agonist-activated cation channels in ileal myocytes.

Novel agonistic action of mustard oil on recombinant and endogenous porcine transient receptor potential V1 (pTRPV1) channels.

Neurogenic components play a crucial role in inflammation and nociception. Mustard oil (MO) is a pungent plant extract from mustard seed, horseradish and wasabi, the main constituent of which is allylisothiocyanate. We have characterized the action of MO on transient receptor potential V1 (TRPV1), a key receptor of signal transduction pathways in the nociceptive system, using fura-2-based [Ca(2+)](i) imaging and the patch-clamp technique in a heterologous expression system and sensory neurons. In human embryonic kidney (HEK) 293 cells expressing porcine TRPV1 (pTRPV1), MO evoked increases of [Ca(2+)](i) in a concentration-dependent manner. A high concentration of MO elicited irreversible cell swelling. Capsazepine, ruthenium red and iodoresiniferatoxin dose-dependently suppressed the MO-induced [Ca(2+)](i) increase. MO elicited outward rectified currents in pTRPV1-expressing HEK 293 cells with a reversal potential similar to that of capsaicin. [Ca(2+)](i) responses to MO were completely abolished by the removal of external Ca(2+). MO simultaneously elicited an inward current and increase of [Ca(2+)](i) in the same cells, indicating that MO promoted Ca(2+) influx through TRPV1 channels. In cultured porcine dorsal root ganglion (DRG) neurons, MO elicited a [Ca(2+)](i) increase and inward current. Among DRG neurons responding to MO, 85% were also sensitive to capsaicin. The present data indicate that MO is a novel agonist of TRPV1 channels, and suggest that the action of MO in vivo may be partly mediated via TRPV1. These results provide an insight into the TRPV1-mediated effects of MO on inflammation and hyperalgesia.

Involvement of adenosine in depression of synaptic transmission during hypercapnia in isolated spinal cord of neonatal rats.

Adenosine is one of the most important neuromodulators in the CNS, both under physiological and pathological conditions. In the isolated spinal cord of the neonatal rat in vitro, acute hypercapnic acidosis (20% CO2, pH 6.7) reversibly depressed electrically evoked spinal reflex potentials. This depression was partially reversed by 8-cyclopentlyl-1,3-dimethylxanthine (CPT), a selective A1 adenosine receptor antagonist. Isohydric hypercapnia (20% CO2, pH 7.3), but not isocapnic acidosis (5% CO2, pH 6.7), depressed the reflex potentials, which were also reversed by CPT. An ecto-5'-nucleotidase inhibitor did not affect the hypercapnic acidosis-evoked depression. An inhibitor of adenosine kinase, but not deaminase, mimicked the inhibitory effect of hypercapnic acidosis on the spinal reflex potentials. Accumulation of extracellular adenosine and inhibition of adenosine kinase activity were caused by hypercapnic acidosis and isohydric hypercapnia, but not isohydric acidosis. These results indicate that the activation of adenosine A1 receptors is involved in the hypercapnia-evoked depression of reflex potentials in the isolated spinal cord of the neonatal rat. The inhibition of adenosine kinase activity is suggested to cause the accumulation of extracellular adenosine during hypercapnia.

Pars plana vitrectomy and panretinal photocoagulation combined with trabeculectomy for successful treatment of neovascular glaucoma.

BACKGROUND: Treatment of neovascular glaucoma (NVG) must be focused on the reduction of intraocular pressure (IOP) and prompt application of pan retinal photocoagulation (PRP). A combination of complete PRP during vitrectomy with trabeculectomy should theoretically be a better method to lower the IOP rapidly in eyes with NVG. The purpose of our study is to assess the efficacy of combining pars plana vitrectomy and PRP with trabeculectomy assisted by mitomycin C (MMC) on NVG eyes secondary to diabetic retinopathy. METHODS: Twenty-five eyes with NVG associated with diabetic retinopathy had pars plana vitrectomy, followed by PRP and trabeculectomy with MMC. The eyes were divided into two groups: nine eyes with vitreous hemorrhage, fibrovascular membrane and/ or retinal detachment were placed in the Proliferation group; and 16 eyes without vitreous hemorrhage, fibrovascular membrane, or retinal detachment were placed in the PC (photocoagulation) group. These eyes had vitrectomy performed so that PRP could be safely performed from ora to ora. The surgical outcome in the two groups was assessed by Kaplan-Meier survival analysis. The criteria for success were a postoperative intraocular pressure (IOP) < or =21 mmHg and a preservation of light perception. RESULTS: In the Proliferation group, Kaplan-Meier life-table analysis showed that the success rate was 55.6% after 1 year and 18.5% after 2 years. The success rate in the PC group was 81.2% from 1 to 3 years after surgery. The surgical outcome was significantly better in the PC group than in the Proliferation group (P=0.009). In the Proliferation group, four eyes had preoperative vitreous hemorrhage, three eyes had a fibrovascular membrane, and two eyes had a retinal detachment. Three of four eyes with vitreous hemorrhage achieved good IOP control. On the other hand, the IOP of all eyes with retinal detachment and fibrovascular membrane were not lowered significantly. CONCLUSIONS: Complete PRP combined with trabeculectomy with MMC can effectively reduce the elevated IOP in eyes with NVG. However, this combined treatment is not effective in eyes with proliferative membranes and retinal detachments.

P2X2 receptors are essential for [Ca2+]i increases in response to ATP in cultured rat myenteric neurons.

We characterized ATP-induced changes in intracellular Ca2+ concentration ([Ca2+]i) and membrane current in cultured rat myenteric neurons using ratiometric Ca2+ imaging with fura-2 and the whole cell patch-clamp technique, respectively. Neuronal cells were functionally identified by [Ca2+]i responses to high K+ and nicotine, which occurred only in cells positive for neuron-specific protein gene product 9.5 immunoreactivity. ATP evoked a dose-dependent increase of [Ca2+]i that was greatly decreased by the removal of extracellular Ca2+ concentration ([Ca2+]o). The amplitude of the [Ca2+]i response to ATP was reduced by half in the presence of voltage-dependent Ca2+ channel blockers. In [Ca2+]o-free solution, ATP produced a small transient rise in [Ca2+]i similar to that induced by P2Y agonists. At -60 mV, ATP evoked a slowly inactivating inward current that was suppressed by the removal of extracellular Na+ concentration. The current-voltage relation for ATP showed an inward rectification with the reversal potential of about 0 mV. The apparent rank order of potency for the purinoceptor agonist-induced increases of [Ca2+]i was ATP > or = adenosine 5'-O-3-triphosphate > or = CTP > or = 2-methylthio-ATP > benzoylbenzoyl-ATP. A similar potency order was obtained with current responses to these agonists. P2 antagonists inhibited inward currents induced by ATP. Ca2+ and Mg2+ suppressed the ATP-induced current, and Zn2+, Cu2+, and protons potentiated it. RT-PCR and immunocytochemical studies showed the expression of P2X2 receptors in cultured rat myenteric neurons. These results suggest that ATP mainly activates ionotropic P2X2 receptors, resulting in a [Ca2+]i increase dependent on [Ca2+]o in rat myenteric neurons. A small part of the ATP-induced [Ca2+]i increase may be also mediated via a P2Y receptor-related mechanism.

Involvement of mitochondrial Na+-Ca2+ exchange in intracellular Ca2+ increase induced by ATP in PC12 cells.

The involvement of mitochondrial Na+-Ca2+ exchange in Ca2+ responses to ATP was examined in rat pheochromocytoma (PC) 12 cells. Intracellular Ca2+ ([Ca2+]i) and Na+ concentrations ([Na+]i) were measured using fura-2 and SBFI, respectively. ATP caused concentration-dependent increases in [Ca2+]i and [Na+]i. High concentrations of ATP elicited a Ca2+ transient followed by a slow recovery of [Ca2+]i (a sustained phase) in 77% of PC12 cells. The sustained phase of Ca2+ response appeared only when the peak Ca2+ transient exceeded 500 nM. FCCP, a protonophore, greatly enhanced Ca2+ responses to ATP only in cells with the sustained phase but not without this phase. The sustained phase was decreased by clonazepam and CGP37157, mitochondrial Na+-Ca2+ exchange inhibitors, and extracellular Na+ removal but not by cyclosporin A, an inhibitor of permeability transition pores. The reintroduction of Na+ 3.5 min after ATP stimulation in the absence of Na+ caused Na+ concentration-dependent increases in [Ca2+]i and [Na+]i. The increase in [Na+]i was correlated with that in [Ca2+]i. FCCP caused a great increase in [Ca2+]i 4.5 min after ATP stimulation in the absence of extracellular Na+ but not in its presence, indicating that mitochondria retain Ca2+ in the absence of Na+. These results suggest that ATP causes a large increase in [Ca2+]i which was sequestered in mitochondria and that the sustained phase of Ca2+ response to ATP are mainly due to the release of mitochondrial Ca2+ through Na+-Ca2+ exchangers in PC12 cells.

Ca2+ store-independent augmentation of [Ca2+]i responses to G-protein coupled receptor activation in recombinantly TRPC5-expressed rat pheochromocytoma (PC12) cells.

Mammalian homologues of the Drosophila canonical transient receptor potential (trp) protein (TRPC) have been implicated to function as receptor-operated Ca(2+) channels (ROCs) or store-operated Ca(2+) channels (SOCs). To determine the role of TRPC5 protein in neural cells, TRPC5 was recombinantly expressed in rat pheochromocytoma cells (PC12) and changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) and Na(+) concentration ([Na(+)](i)) were analyzed. TRPC1 and TRPC3 mRNAs were endogenously expressed in PC12 cells. In TRPC5-expressed cells (TRPC5-cells), the resting [Ca(2+)](i) and [Na(+)](i) were significantly higher than those in control cells. The [Ca(2+)](i) increases induced by bradykinin and uridine 5'-triphosphate were significantly larger in TRPC5-cells. TRPC5 expression did not change in store-operated Ca(2+) entry elicited by thapsigarigin. TRPC5-cells showed larger inward current and increase of [Na(+)](i) in response to BK than control cells. These results suggest that TRPC5 channels expressed in PC12 cells function as ROCs activated by G-protein/phospholipase C coupled receptors, but not as SOCs.

Two distinct inhibitory actions of steroids on cholinoceptor-mediated secretion of catecholamine from guinea-pig adrenal medullary cells.

We investigated the effects of dexamethasone, cortisol and aldosterone on responses to nicotine and muscarine in guinea-pig isolated adrenal medullary cells. Nicotine-induced inward currents were reversibly inhibited by these steroids in a dose-dependent and non-competitive manner. These steroids inhibited an increase in [Ca2+](i) in response to nicotine but not muscarine. Muscarine-induced catecholamine secretion was inhibited by cortisol and aldosterone but not dexamethasone. Phorbol 12-myristate 13-acetate, a protein kinase C activator, caused catecholamine secretion which was inhibited by cortisol and aldosterone but not dexamethasone. These results suggest that catecholamine secretion induced by cholinoceptor stimulation is inhibited by steroids via two distinct mechanisms; one is the inhibition of nicotinic receptors, another is the inhibition of protein kinase C activation in guinea-pig adrenal medullary cells.

Relaxant mechanisms of parathyroid hormone in rat mesenteric artery.

The effects of parathyroid hormone (PTH) on tension and intracellular Ca level ([Ca ] ) were examined in ring preparations of rat mesenteric artery using isometric tension recording and the fura-2 method, respectively. The PTH (30 n ) elicited relaxation in arterial rings precontracted by phenylephrine regardless of the presence or absence of endothelium. In the endothelium-denuded arterial rings precontracted by 3 micro M of phenylephrine or 60 m of potassium chloride (KCl), PTH-related protein and PTH produced concentration-dependent relaxation to the same extent, but inhibited contraction induced by phenylephrine more effectively than that induced by KCl. Phenylephrine-induced tonic contraction was changed to a phasic one with decreased peak tension in the presence of PTH. Similar changes were observed with extracellular Ca removal or methoxyverapamil plus SK&F96365, respective of voltage-gated and receptor-operated Ca channel inhibitors. Phenylephrine evoked a concentration-dependent contraction concomitant with an increase in [Ca ]. PTH reduced both responses to the same extent. In a Ca -free solution, PTH inhibited a phasic contraction and a transient increase in [Ca ] in response to phenylephrine but not caffeine. Reverse transcriptase-polymerase chain reaction showed that PTH and PTH receptors were expressed in the rat mesenteric artery. In this tissue, PTH increased cyclic adenosine monophosphate (cAMP) levels. These results suggest that the inhibitory effect of PTH on alpha -adrenoceptor-mediated contraction results from the inhibition of Ca influx through receptor-operated and voltage-gated Ca channels, and Ca release from Ca stores, probably via increased cAMP in the rat mesenteric artery.

Functional relation between caffeine- and muscarine-sensitive Ca2+ stores and no Ca2+ releasing action of cyclic adenosine diphosphate-ribose in guinea-pig adrenal chromaffin cells.

In voltage-clamped guinea-pig chromaffin cells, muscarine (50 microM) or caffeine (30 mM) produced a transient intracellular Ca(2+) concentration ([Ca(2+)](i)) increase, catecholamine release and an outward K(+) current mediated through Ca(2+) released from internal Ca(2+) stores at a holding potential of -40 mV. Caffeine followed by muscarine failed to evoke these responses, while muscarine followed by caffeine was effective in producing about 30% of [Ca(2+)](i) increase and catecholamine secretion. In cells dialyzed with inositol 1,4,5-trisphosphate (IP(3)), caffeine failed to produce the [Ca(2+)](i) increase. Intracellular application of cyclic adenosine 5'-diphosphate-ribose (cADP-ribose) or 8-bromo cADP-ribose exerted no effect on the resting [Ca(2+)](i) and the caffeine-induced [Ca(2+)](i) increase. These results suggest that IP(3)-sensitive stores are functionally divided into two subpopulations, sensitive and insensitive to caffeine, and it is unlikely that cADP-ribose plays a role as a Ca(2+) releaser in guinea-pig adrenal chromaffin cells.