Astilbin lowers the effective caffeine dose for decreasing lipid accumulation via activating AMPK in high-fat diet-induced obese mice

BACKGROUND

Caffeine has an anti-obesity effect, although chronic excessive caffeine consumption also causes caffeinism, which is marked by increased anxiety or depression, amongst other symptoms. The present study aimed to investigate whether the addition of flavonoids such as astilbin can reduce the caffeine dose needed to inhibit obesity.

RESULTS

ICR mice (n = 80) were fed with normal diet, high-fat diet (HFD), HFD supplemented with astilbin, caffeine, or astilbin + caffeine for 12 weeks. When diets supplemented with astilbin, 0.3 g kg^-1 diet caffeine had the same effect as 0.6 g kg^-1 diet caffeine alone, and 0.6 g kg^-1 diet caffeine combined with astilbin most effectively inhibited HFD-induced obesity. Astilbin improved the anti-obesity effects of caffeine on lipid accumulation via the activation of AMP-activated protein kinase α (AMPKα). (i) Activated AMPKα decreased lipid biosynthesis by suppressing the activity or mRNA expression of 3-hydroxy-3-methylglutaryl-CoA reductase, sterol regulatory element binding protein 1c and its target gene fatty acid synthase. (ii) Activated AMPKα also up-regulated lipolysis by enhancing the expression of adipose triglyceride lipase and increasing the phosphorylation of hormone-sensitive lipase. (iii) Finally, activated AMPKα increased carnitine acyltransferase and acyl-CoA oxidase activities, which further promoted fatty acid β-oxidation.

CONCLUSION

The results obtained in the present study indicate that astilbin may decrease the effective dose of caffeine needed for an anti-obesity effect and also suggest that it suppresses fat accumulation via the activation of AMPK. © 2020 Society of Chemical Industry.

Effects of caffeine on behavioral and inflammatory changes elicited by copper in zebrafish larvae: Role of adenosine receptors

This study investigated the effects of caffeine in the behavioral and inflammatory alterations caused by copper in zebrafish larvae, attempting to correlate these changes with the modulation of adenosine receptors. To perform a survival curve, 7dpf larvae were exposed to 10μM CuSO₄, combined to different concentrations of caffeine (100μM, 500μM and 1mM) for up to 24h. The treatment with copper showed lower survival rates only when combined with 500μM and 1mM of caffeine. We selected 4 and 24h as treatment time-points. The behavior evaluation was done by analyzing the traveled distance, the number of entries in the center, and the length of permanence in the center and the periphery of the well. The exposure to 10μM CuSO₄ plus 500μM caffeine at 4 and 24h changed the behavioral parameters. To study the inflammatory effects of caffeine, we assessed the PGE₂ levels by using UHPLC-MS/MS, and TNF, COX-2, IL-6 and IL-10 gene expression by RT-qPCR. The expression of adenosine receptors was also evaluated with RT-qPCR. When combined to copper, caffeine altered inflammatory markers depending on the time of exposure. Adenosine receptors expression was significantly increased, especially after 4h exposure to copper and caffeine together or separately. Our results demonstrated that caffeine enhances the inflammation induced by copper by decreasing animal survival, altering inflammatory markers and promoting behavioral changes in zebrafish larvae. We also conclude that alterations in adenosine receptors are related to those effects.

Decreased Caffeine-Induced Locomotor Activity via Microinjection of CART Peptide into the Nucleus Accumbens Is Linked to Inhibition of the pCaMKIIa-D3R Interaction

The purpose of this study was to characterize the inhibitory modulation of cocaine- and amphetamine-regulated transcript (CART) peptides, particularly with respect to the function of the D3 dopamine receptor (D3R), which is activated by its interaction with phosphorylated CaMKIIα (pCaMKIIα) in the nucleus accumbens (NAc). After repeated oral administration of caffeine (30 mg/kg) for five days, microinjection of CART peptide (0.08 μM/0.5 μl/hemisphere) into the NAc affected locomotor behavior. The pCaMKIIα-D3R interaction, D3R phosphorylation and cAMP/PKA/phosphorylated CREB (pCREB) signaling pathway activity were measured in NAc tissues, and Ca2+ influx and pCaMKIIα levels were measured in cultured NAc neurons. We found that CART attenuated the caffeine-mediated enhancement of depolarization-induced Ca2+ influx and CaMKIIα phosphorylation in cultured NAc neurons. Repeated microinjection of CART peptides into the NAc decreased the caffeine-induced enhancement of Ca2+ channels activity, pCaMKIIα levels, the pCaMKIIα-D3R interaction, D3R phosphorylation, cAMP levels, PKA activity and pCREB levels in the NAc. Furthermore, behavioral sensitization was observed in rats that received five-day administration of caffeine following microinjection of saline but not in rats that were treated with caffeine following microinjection of CART peptide. These results suggest that caffeine-induced CREB phosphorylation in the NAc was ameliorated by CART peptide due to its inhibition of D3R phosphorylation. These effects of CART peptides may play a compensatory role by inhibiting locomotor behavior in rats.

Recent caffeine ingestion reduces adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia

OBJECTIVES

Caffeine, an adenosine receptor blocker, should theoretically reduce adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia (SVT). We aimed to determine the effect of recent caffeine ingestion on the likelihood of reversion of SVT with adenosine.

METHODS

This was a multicenter, case-control study of adult patients with SVT treated with adenosine between September 2007 and July 2008. The primary endpoint was reversion to sinus rhythm (SR) after a 6-mg adenosine bolus, as a function of recent (within 2, 4, 6, and 8 hours) caffeine ingestion. Caffeine ingestion data were collected using a self-administered questionnaire.

RESULTS

Of 68 patients enrolled, 52 (76.5%, 95% confidence interval [CI] = 64.4% to 85.6%) reverted after a 6-mg adenosine bolus. There were no significant differences in age, sex, or daily caffeine ingestion between patients who did and did not revert (p > 0.05). However, as a group, patients who did not revert had recently ingested significantly more caffeine (p < 0.05). If caffeine had been ingested less than 2 or 4 hours before the adenosine bolus, the odds of reversion to SR were significantly reduced (odds ratio [OR] = 0.18, 95% CI = 0.04 to 0.93; and OR = 0.14, 95% CI = 0.04 to 0.49, respectively). If caffeine had been ingested less than 6 or 8 hours before the adenosine, the odds of reversion were not reduced (OR = 0.31, 95% CI = 0.09 to 1.02; and OR = 0.31, 95% CI = 0.09 to 1.08, respectively).

CONCLUSIONS

Ingestion of caffeine less than 4 hours before a 6-mg adenosine bolus significantly reduces its effectiveness in the treatment of SVT. An increased initial adenosine dose may be indicated for these patients.

Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together

RATIONALE

Although both contain behaviourally significant concentrations of caffeine, tea is commonly perceived to be a less stimulating drink than coffee. At least part of the explanation for this may be that theanine, which is present in tea but not coffee, has relaxing effects. There is also some evidence that theanine affects cognitive performance, and it has been found to reduce blood pressure in hypertensive rats.

OBJECTIVES

To study the subjective, behavioural and blood pressure effects of theanine and caffeine administered alone and together, in doses relevant to the daily tea consumption of regular tea drinkers.

MATERIALS AND METHODS

In a randomised, double-blind, placebo-controlled study, healthy adult participants (n = 48) received either 250-mg caffeine, 200-mg theanine, both or neither of these. They completed ratings of mood, including anxiety, and alertness, and had their blood pressure measured before and starting 40 min after drug administration. Anxiety was also assessed using a visual probe task.

RESULTS

Caffeine increased self-rated alertness and jitteriness and blood pressure. Theanine antagonised the effect of caffeine on blood pressure but did not significantly affect jitteriness, alertness or other aspects of mood. Theanine also slowed overall reaction time on the visual probe task.

CONCLUSIONS

Theanine is a physiologically and behaviourally active compound and, while it is unclear how its effects might explain perceived differences between tea and coffee, evidence suggests that it may be useful for reducing raised blood pressure.

Extract of Hypericum perforatum blocks caffeine-induced locomotor activity in mice: a possible role of nitric oxide

The present study investigated the effects of HPE on caffeine-induced locomotor activity in mice. Caffeine (4-16 mg/kg) or saline were given to adult male Swiss-Webster mice, and the locomotor activity was immediately measured for 30 min. HPE (6-48 mg/kg) and saline were injected to another group of mice and the locomotor activity was measured 20 min later. HPE (6-24 mg/kg) was also administered to another group of mice 20 min before caffeine (16 mg/kg) injections and the locomotor activity was recorded for 30 min immediately after caffeine administrations. Finally l-arginine (1 g/kg) was administered i.p. 20 min before HPE (6 mg/kg) and the locomotor activity was measured as mentioned above. Each group of mice was used only once. Caffeine produced some significant increases in locomotor activity of the mice. HPE (6-24 mg/kg) significantly blocked the caffeine-induced locomotor hyperactivity. Pretreatment of l-arginine (1 g/kg) reversed the inhibitory effect of HPE (6 mg/kg) on caffeine-induced locomotor activity without producing any significant effect on locomotor activity of the mice when it was administered alone. The results suggest that HPE blocks caffeine-induced locomotor hyperactivity in mice. Furthermore, the inhibitory effect of HPE on caffeine-induced locomotor activity may be related to its NOS inhibitory property.

Ca2+ sparks and Ca2+ glows in superior cervical ganglion neurons

AIM

Ca2+ release from the endoplasmic reticulum (ER) is an integral component of neuronal Ca2+ signaling. The present study is to investigate properties of local Ca2+ release events in superior cervical ganglion (SCG) neurons.

METHODS

Primary cultured SCG neurons were prepared from neonatal rats (P3-P7). Low concentration of caffeine was used to induce Ca2+ release from the ER Ca2+ store, and intracellular Ca2+ was recorded by high-resolution line scan confocal imaging and the Ca2+ indicator Fluo-4.

RESULTS

Two populations of local Ca2+ release events with distinct temporal characteristics were evoked by 1.5 mmol/L caffeine near the surface membrane in the soma and the neurites of SCG neurons. Brief events similar to classic Ca2+ sparks lasted a few hundreds of milliseconds, whereas long-lasting events displayed duration up to tens of seconds. Typical somatic and neurite sparks were of 0.3- and 0.52-fold increase in local Fluo-4 fluorescence, respectively. Typical Ca2+ glows were brighter (deltaF/F0 approximately 0.6), but were highly confined in space. The half maximum of full duration of neurite sparks was much longer than those in the soma (685 vs 381 ms).

CONCLUSION

Co-existence of Ca2+ sparks and Ca2+ glows in SCG neurons indicates distinctive local regulation of Ca2+ release kinetics. The local Ca2+ signals of variable, site-specific temporal length may bear important implications in encoding a 'memory' of the trigger signal.

Estrogen prevents neuroprotection by caffeine in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease

Epidemiological studies have strongly linked caffeine consumption with a reduced risk of developing Parkinson's disease (PD) in men. Interestingly, in women, this inverse association is present only in those who have not taken postmenopausal estrogens, suggesting an interaction between the influences of estrogen and caffeine use on the risk of PD. To explore a possible biological basis for this interaction, we systematically investigated how the neuroprotective effect of caffeine is influenced by gender, ovariectomy (OVX), and then exogenous estrogen in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. (1) Caffeine treatment produced a dose-dependent attenuation of MPTP-induced striatal dopamine loss in both young and retired breeder (RB) male, but not female, mice. (2) In female mice (both young and RB), caffeine was less potent or altogether ineffective as a neuroprotectant after sham surgery compared to OVX or after OVX plus estrogen replacement compared to OVX plus placebo treatment. (3) Estrogen treatment also prevented the protection of caffeine against dopamine loss in young male mice. (4) Consistent with the putative protective effect of estrogen, female and OVX plus estrogen mice were relatively resistant to MPTP toxicity compared to male and OVX plus placebo mice, respectively. (5) There was no overall difference in brain levels of caffeine and its metabolites between OVX plus placebo and OVX plus estrogen mice. Together, these results suggest that estrogen can occlude and thereby prevent the neuroprotective effect of caffeine in a model of PD neurodegeneration, supporting a biological basis for the interaction between estrogen and caffeine in modifying the risk of PD.

Nicotine antagonizes caffeine- but not pentylenetetrazole-induced anxiogenic effect in mice

RATIONALE

Nicotine and caffeine are widely consumed licit psychoactive drugs worldwide. Epidemiological studies showed that they were generally used concurrently. Although some studies in experimental animals indicate clear pharmacological interactions between them, no studies have shown a specific interaction on anxiety responses.

OBJECTIVES

The present study investigates the effects of nicotine on anxiety induced by caffeine and another anxiogenic drug, pentylenetetrazole, in mice. The elevated plus-maze (EPM) test was used to evaluate the effects of drugs on anxiety.

METHODS

Adult male Swiss Webster mice (25-32 g) were given nicotine (0.05-0.25 mg/kg s.c.) or saline 10 min before caffeine (70 mg/kg i.p.) or pentylenetetrazole (15 and 30 mg/kg i.p.) injections. After 15 min, mice were evaluated for their open- and closed-arm time and entries on the EPM for a 10-min session. Locomotor activity was recorded for individual groups by using the same treatment protocol with the EPM test.

RESULTS

Nicotine (0.05-0.25 mg/kg) itself did not produce any significant effect in the EPM test, whereas caffeine (70 mg/kg) and pentylenetetrazole (30 mg/kg) produced an anxiogenic effect, apparent with decreases in open-arm time and entry. Nicotine (0.25 mg/kg) pretreatment blocked the caffeine- but not pentylenetetrazole-induced anxiety. Administration of each drug and their combinations did not produce any effect on locomotor activity.

CONCLUSIONS

Our results suggest that the antagonistic effect of nicotine on caffeine-induced anxiety is specific to caffeine, instead of a non-specific anxiolytic effect. Thus, it may extend the current findings on the interaction between nicotine and caffeine.

Reactive blue prevented caffeine-induced neurotoxicity by an independent mechanism from intracellular calcium currents in cell culture from auditory cortex of rats

Neurotoxicity induced by caffeine in auditory-neuron cultures was studied in rat pups. For possible protective effect, reactive blue (RB) alone and in combination with dantrolene were tested in subsequent doses. RB was found to have a U-shape neuroprotective effect in caffeine neurotoxicity. Dantrolene was also tested in combined application in caffeine neurotoxicity. Despite the existing neuroprotection, no additional protection was obtained with various doses of dantrolene. In conclusion, RB may exert neuroprotective effect by increasing intracellular ATP levels in caffeine toxicity. High ATP levels may postpone the toxic cascade. Dantrolene as an endoplasmic reticulum calcium release blocker had no additional protective effect, suggesting that the increased intracellular calcium levels may be involved in later states of the toxic cascade, occurring after the compensatory phase of the cell death.

Caffeine-induced epileptiform field potentials in rat hippocampal slices: a pharmacological characterization

Pharmacological modulation of the epileptiform electric activity induced by caffeine, 10 mM (CAF) on rat hippocampal slices was studied upon field potential recordings in CA3 area of the slices. This concentration of CAF, reportedly releasing Ca2+ ions from the endoplasmic reticulum, led single fimbrial stimuli to evoke repetitive population spikes (PSs) and induced periodic spontaneous field bursts. Carbamazepine, 50 microM reduced (by <40%) the number of repetitive PSs and the rate of spontaneous bursting, with no significant effect on the amplitude of evoked and spontaneous bursts. Valproate, 1 mM reduced only the number (by approximately 25%), but not the amplitudes, of repetitive PSs. Clonazepam, 1 microM consistently reduced the number of repetitive PSs (by approximately 45%), their amplitudes (by 30-60%), and the amplitude of spontaneous bursts (by approximately 70%). The adenosine receptor agonists 2-chloroadenosine, 5 microM and R(-) N6-(2-phenylisopropyl)adenosine, 1 microM had only scanty anti-CAF activity. The depletor of intracellular Ca2+ stores, thapsigargin, 2 microM transiently inhibited the number of evoked PSs and spontaneous bursting. The blocker of ryanodine receptor opening, ruthenium red had an anti-CAF effect, modest at 30 microM, but very strong at 40 microM. Nifedipine, 20 microM opposed CAF-induced spontaneous bursting, but not the evoked PSs. Flunarizine, 50 microM presented only a transient tendency to delay spontaneous bursting. In conclusion, this in vitro slice model appears readily able to reveal antiepileptic properties, though it does not support unequivocal mechanistic interpretation. Nevertheless, anti-CAF activity in this model would suggest the likely involvement of the neuronal ryanodine receptor-related traffic of calcium.

1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid (BAPTA-AM) inhibits caffeine-induced apoptosis in human neuroblastoma cells

In the present study, it was investigated whether 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid (BAPTA-AM), an intracellular Ca(2+) chelator, possesses protective effect against caffeine-induced apoptosis in the central nervous system. Through morphological and biochemical analyses, cells treated with caffeine exhibited several apoptotic features. On the other hand, cells treated with caffeine and BAPTA-AM, showed decreased occurrence of apoptotic features. In addition, it was shown that BAPTA-AM treatment inhibits caffeine-induced increase of caspase-3 enzyme activity. These results show that caffeine induces apoptotic death in human SK-N-MC neuroblastoma cells and BAPTA-AM prevents apoptosis by attenuating caffeine-induced caspase-3 activation.

Inhibition of caffeine biosynthesis in tea (Camellia sinensis) and coffee (Coffea arabica) plants by ribavirin

The effects of ribavirin, an inhibitor of inosine-5'-monophosphate (IMP) dehydrogenase, on [8-(14)C]inosine metabolism in tea leaves, coffee leaves and coffee fruits were investigated. Incorporation of radioactivity from [8-(14)C]inosine into purine alkaloids, such as theobromine and caffeine, guanine residues of RNA, and CO(2) was reduced by ribavirin, while incorporation into nucleotides, including IMP and adenine residues of RNA, was increased. The results indicate that inhibition of IMP dehydrogenase by ribavirin inhibits both caffeine and guanine nucleotide biosynthesis in caffeine-forming plants. The use of IMP dehydrogenase-deficient plants as a potential source of good quality caffeine-deficient tea and coffee plants is discussed.

Dissociative antagonistic effects of caffeine on alcohol-induced impairment of behavioral control

The present study examined the separate and combined effects of alcohol and caffeine on behavioral control in a context in which preliminary cues signaled the likelihood that a response should be executed or inhibited. Social drinkers (N = 12) performed a cued go/no-go task that measured control as the quick execution of responses to go targets and sudden suppression of responses to no-go targets. Performance was tested under 3 doses of caffeine (0.0 mg/kg, 2.0 mg/kg, and 4.0 mg/kg) in combination with 2 doses of alcohol (0.0 g/kg and 0.65 g/kg). Alcohol impaired both inhibitory and activational aspects of behavioral control. Caffeine antagonized alcohol effects on response execution but had no effect on inhibitory control. The findings highlight potential differences in how activational and inhibitory aspects of behavioral control respond to drug interactions.

The modulatory actions of dopamine D2/3 agonists and antagonists on the locomotor-activating effects of morphine and caffeine in mice

Morphine produces robust increases in locomotor activity in mice. Recent data indicate that dopamine (DA) D2/3 agonists attenuate the discriminative stimulus and antinociceptive effects of mu opioid agonists such as morphine. The present study was designed to determine the extent to which D2/3 receptor activation and blockade can modulate morphine-induced locomotion using a novel cumulative dosing procedure in Swiss-Webster mice. The results indicate that morphine-induced locomotion is nonsignificantly attenuated by the D2/3 agonists quinelorane and quinpirole, whereas the D2/3 antagonists eticlopride and nafadotride, as well as the partial D2/3 agonist BP897, significantly reduced morphine-induced locomotion. To determine the specificity of this modulation, these agonists and antagonists were examined in combination with caffeine, a drug that also indirectly alters DAergic activity. Unlike the effects on morphine, caffeine-induced locomotion was unaltered by eticlopride, nafadotride and BP897, but was attenuated by quinelorane and quinpirole. These results indicate that modulation of D2/3 receptors can, in turn, alter the locomotor-activating effects of morphine.

Use of oral contraceptives blunts the calciuric effect of caffeine in young adult women

Caffeine consumption increases the urinary excretion of calcium and other minerals. Factors that affect caffeine metabolism such as steroid hormones may modify this effect. The purpose of this study was to evaluate the influence of oral contraceptive (OC) use on the 4-h urinary excretion of calcium, phosphorus, magnesium, zinc, sodium, potassium and caffeine metabolites in response to a high caffeine dose given as coffee beverage. Adult women, 20-29 y, users (+OC, n = 15) and nonusers (-OC, n = 15) of oral contraceptives, with calcium intake approximately 500 mg/d, participated in two tests, caffeine load (5 mg/kg body weight) and no-caffeine control, in a randomized crossover design. The net increase (caffeine load corrected by no caffeine) in urinary excretion of most minerals was significantly higher in -OC than in +OC (P < 0.05), with the larger group difference for calcium (ninefold) followed by magnesium (twofold), zinc (onefold) and potassium (onefold). Net increases in urinary excretion of 1-methylurate and paraxanthine were about three- and fivefold higher, respectively, in -OC than in +OC (P < 0.05) whereas net increases in urinary excretion of 5-acetylamino-6-formylamino-3-methyluracil (AFMU) and 1,7-dimethylurate were over twofold higher in the +OC than in -OC (P < 0.05). Following the caffeine load, most urinary minerals showed negative correlation with urinary 1-methylurate in -OC (R </= -0.78, P < 0.01), and with urinary AFMU and 1,7-dimethylurate in +OC (R </= -0.84, P < 0.01). Oral contraceptives appear to limit the renal effect of caffeine on mineral excretion possibly by reducing paraxanthine excretion, the most active caffeine metabolite.

Effect of tetrandrine on free intracellular calcium in cultured calf basilar artery smooth muscle cells

AIM

To study the effects of tetrandrine (Tet) on extracellular Ca2+ influx and intracellular Ca2+ release in cultured calf basilar artery smooth muscle cells.

METHODS

Free intracellular calcium was examined by a system of measurement of AR-CM-MIC, using Fura 2-AM as a fluorescent indicator.

RESULTS

In the presence of extracellular Ca2+ 1.3 mmol/L, no significant effect of Tet on resting [Ca2+]i was found. KCl 20, 40, and 60 mmol/L triggered a sustained rise in [Ca2+]i, pretreatment with Tet inhibited the elevation of [Ca2+]i induced by KCl in concentration-dependent manner, Tet at high concentration (100 micromol/L) almost abolished the rise of [Ca2+]i evoked by KCl. Caffeine 10 mmol/L only produced a transient increase of [Ca2+]i, which spontaneously declined back to resting levels. Tet 10-30 micromol/L had no effect on caffeine-induced [Ca2+]i transient peak. Tet at high concentration (100 micromol/L), however, reduced the [Ca2+]i transient peak induced by caffeine. Phenylephrine (PE) 10 mmol/L produced a rapid transient peak and a distinct sustained elevation in [Ca2+]i in the presence of extracellular Ca2+. In the absence of extracellular Ca2+ containing egtazic acid (EGTA), PE only produced a rapid transient peak in [Ca2+]i. Pretreatment of Tet (10-100 micromol/L) inhibited the sustained elevation in [Ca2+]i induced by PE in a concentration-dependent manner. However, only 100 micromol/L of Tet inhibited the transient peak in [Ca2+]i induced by PE both in the presence of extracellular Ca2+ 1.3 mmol/L and in the absence of extracellular Ca2+ containing EGTA.

CONCLUSION

Tet inhibited the Ca2+ influx from the extracellular site via voltage-activated Ca2+ channel and PE-receptor-operated Ca2+ channel. At a high concentration, Tet may inhibit the Ca2+ release from sarcoplasmic reticulum (SR) or refilling of intracellular calcium store in cerebral artery smooth muscle cells.

Inhibition of caffeine-induced Ca2+ release by adenosine in mammalian skinned slow- and fast-twitch fibres

The present study performed on chemically skinned skeletal fibres was designed to compare the effects of adenosine on the Ca2+ sensitivity of contractile proteins and on caffeine-induced Ca2+ release in rat slow- (soleus) and fast-twitch (edl) muscles. The tension-pCa relationships were obtained by exposing triton X-100 (1% v/v) skinned fibres sequentially to solutions of decreasing pCa in the presence or in absence of adenosine. Then, changes in caffeine contracture due to adenosine were recorded on saponin (50 microg/ml) skinned fibres. The results show that the sensitivity to Ca2+ of contractile proteins in the presence of different concentrations of caffeine was not significantly modified by adenosine. However, it was proposed that adenosine (0.1-2 mM) reduced the Ca2+ released by caffeine (0.1-10 mM) from the sarcoplasmic reticulum in slow- and fast-twitch fibres and that the soleus was more sensitive to adenosine than edl muscle. The effects of specific A2a and A1 agonists and antagonists were also tested on caffeine contractures. It was found that the A1 antagonist reduced adenosine effect on caffeine response. Then it is proposed that adenosine modulates the sarcoplasmic reticulum Ca2+ release by a direct effect on the RyR1 receptors and/or by an indirect effect mediated by A1 receptors located at the sarcoplasmic level.

Modulation of a voltage-gated calcium channel linked to activation of glutamate receptors and calcium-induced calcium release in the catfish retina

1. Catfish (Ictalurus punctatus) retinal cone horizontal cells contain an L-type calcium current that has been proposed to be involved in visual processing. Here we report on the modulation of this current by activation of glutamate receptors and calcium-induced calcium release (CICR) from intracellular calcium stores. 2. Fluorescence data obtained from isolated horizontal cells loaded with indo-1 provided evidence of calcium release from an intracellular calcium store sensitive to caffeine, calcium and ryanodine. In the presence of caffeine, ryanodine-sensitive stores released calcium in a transient manner. Release of calcium was blocked when cells were preincubated in BAPTA, in the presence of ruthenium red, or in low concentrations of ryanodine. 3. The release of calcium from ryanodine-sensitive stores directly corresponded with a decrease of the voltage-gated L-type calcium current amplitude. Caffeine-induced modulation of the calcium current was reduced in the presence of ruthenium red. 4. Activation of ionotropic kainate receptors on catfish cone horizontal cells triggered CICR from ryanodine-sensitive stores and mimicked inhibition of the voltage-gated calcium current. Kainate-induced inhibition of the calcium current was diminished when intracellular calcium stores were inhibited with ruthenium red or depleted with ryanodine, or when calmodulin antagonists or CaM kinase II inhibitors were present. 5. These results provide evidence that activation of an ionotropic glutamate receptor on catfish cone horizontal cells is linked to calcium release from ryanodine-sensitive intracellular calcium stores and modulation of the L-type calcium current activity. Inhibition of this calcium current directly or indirectly involves calmodulin and CaM kinase II and represents a possible mechanism used by horizontal cells to affect response properties of these cells.

Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat

In this study, the inhibiting action of theanine on the excitation by caffeine at the concentration regularly associated with drinking tea was investigated using electroencephalography (EEG) in rats. First, the stimulatory action by caffeine i.v. administration at a level higher than 5 micromol/kg (0.970 mg/kg) b.w. was shown by means of brain wave analysis, and this level was suggested as the minimum dose of caffeine as a stimulant. Next, the stimulatory effects of caffeine were inhibited by an i.v. administration of theanine at a level higher than 5 micromol/kg (0.781 mg/kg) b.w., and the results suggested that theanine has an antagonistic effect on caffeine's stimulatory action at an almost equivalent molar concentration. On the other hand, the excitatory effects were shown in the rat i.v. administered 1 and 2 micromol/kg (0.174 and 0.348 mg/kg) b.w. of theanine alone. These results suggested two effects of theanine, depending on its concentration.

Effects of berbamine on intracellular calcium concentration in cultured HeLa cells

AIM

To study the involvement of Ca2+ signaling and the effects of berbamine (Ber) on intracellular calcium concentration ([Ca2+]i) elevated in cultured HeLa cells.

METHODS

[Ca2+]i was measured by confocal microscopy in single HeLa cell loaded with Fluo 3-AM. The change of [Ca2+]i was represented by fluorescent intensity (FI).

RESULTS

(1) In the presence of extracellular Ca2+ 1.3 mmol.L-1, the resting level of FI was 186 +/- 44, n = 49 cells from all control experiments, and KCl, NE, caffeine, and calcimycin (Cal) all induced [Ca2+]i elevations in cultured HeLa cells. (2) The resting level of FI was not affected by pretreatment with Ber. The FI increased by KCl 60 mmol.L-1, NE 100 micromol.L-1, and Cal 30 micromol.L-1 were attenuated (P < 0.05 or P < 0.01), the slope and the time to peak of FI increase were decreased and prolonged. (3) In the absence of extracellular Ca2+, caffeine 80 mmol.L-1-induced [Ca2+]i mobilization was not inhibited by Ber 100 micromol.L-1 pretreatment. (4) These effects of Ber were similar to those of verapamil (Ver) 10 mumol.L-1.

CONCLUSION

Although it was derived from cervical cancer, the HeLa cells which were belong to the nonexcitable cell possessed the similar biological properties with excitable cells, and Ca2+ also played a crucial role in signal transduction processes.

Calcium antagonistic activity of Bacopa monniera on vascular and intestinal smooth muscles of rabbit and guinea-pig

The present study demonstrates the calcium antagonistic activity in ethanol extract of Bacopa monniera. The plant extract inhibited the spontaneous movements of both guinea-pig ileum (IC50 = 24+/-4 microg/ml) and rabbit jejunum (IC50 = 136+/-9 microg/ml). A marked reduction in acetylcholine- and histamine-induced responses (0.0001-10 microM) in the ileum was evident in the presence of extract (260 microg/ml). The acetylcholine (1 microM)-induced contraction in the ileum was also inhibited by the extract (100-700 microg/ml) in a concentration dependent way (IC50 = 285+/-56 microg/ml). All these results indicate a direct action of the extract on smooth muscles. Calcium chloride-induced responses in the rabbit blood vessels and jejunum were attenuated in the presence of plant extract (10-700 microg/ml) implying a direct interference of plant extract with influx of calcium ions in the cells. However, the lack of modification of either noradrenaline- or caffeine-induced contractions in the presence of extract suggests that extract has no detectable effect on mobilization of intracellular calcium. These results indicate that spasmolytic effect of the B. monniera extract in smooth muscles is predominantly due to inhibition of calcium influx via both voltage and receptor operated calcium channels of the cell membrane.

Cyclic ADP-ribose-dependent Ca2+ release is modulated by free [Ca2+] in the scallop sarcoplasmic reticulum

Cyclic ADP-ribose (cADPR) elicits calcium-induced calcium release (CICR) in a variety of cell types. We studied the effect of cADPR on Ca2+ release in muscle cells by incubating SR vesicles from scallop (Pecten jacobaeus) adductor muscle in the presence of the Ca2+ tracer fluo-3. Exposure of SR to cADPR (20 microM) produced Ca2+ release, which was a function of free [Ca2+] in a range between about 150 and 1000 nM, indicating an involvement of ryanodine-sensitive Ca2+ channels. This Ca2+ release was not significantly enhanced by calmodulin (7 micrograms/ml), but it was enhanced by equimolar addition of noncyclic ADPR. Also, the Ca2+ release elicited by cADPR/ADPR was a function of free [Ca2+] in a range between about 150 and 3000 nM, over which Ca2+ was inhibitory. cADPR self-inactivation was observed at low free [Ca2+] (about 150 nM), but it tended to disappear upon [Ca2+] elevation (about 250 nM). Caffeine or ryanodine induced a Ca2+ release which was ruthenium red (2.5 microM) sensitive at low [Ca2+]. However, the Ca2+ release induced by either ryanodine or cADPR was no longer ruthenium red sensitive when free [Ca2+] was increased. Based on these data, a model is proposed for Ca2+ signaling in muscle cells, where a steady-state cADPR level would trigger Ca2+ release when free [Ca2+] does reach a threshold slightly above its resting level, hence producing cascade RyR recruitment along SR cisternae from initial Ca2+ signaling sites.

Experimental treatment of the acute cardiovascular toxicity of caffeine

STUDY DESIGN

The intravenous infusion of caffeine-sodium salicylate (15 mg/kg/min) into artificially ventilated and anesthetized rats caused a progressive fall in arterial blood pressure which was mainly due to a decrease in peripheral resistance. Cardiac output increased initially by 15% but then declined after 30 minutes. The electroencephalogram showed sinus tachycardia and ectopic beats mainly in the form of monomorphic ventricular bigeminy which began after 22.8 minutes. Fatal ventricular fibrillation occurred in all animals by 66.9 +/- 3.1 minutes. Treatment of cardiac arrhythmia by repeated intravenous injections of propranolol (1 mg/kg) or verapamil (1 mg/kg) was effective and prolonged survival time to 91.7 +/- 4.4 or 84.3 +/- 2.9 minutes, respectively (p < 0.05). Propranolol also prolonged survival time when administered in a single dose of 20 mg/kg i.v. 10 minutes before the initiation of caffeine infusions. Repeated administrations of quinidine sulfate (5 mg/kg), phenytoin (5 mg/kg), or lidocaine (1-5 mg/kg), on the other hand, exerted very short antiarrhythmic activity and did not prolong survival time at all. Fluid therapy with polygeline plasma expander (0.5 mL/kg/min) did not influence caffeine-induced cardiovascular failure in any way.

CONCLUSIONS

Ventricular ectopia leading to fibrillation accounts for the lethal outcome of caffeine poisoning in anesthetized rats and can be antagonized by treatment with propranolol or verapamil.

Antagonism of kynurenic acid to anxiogens in mice

In a dark-light chamber in mice, kynurenic acid (KYNA, 200 mg/kg, i.p.), an endogenous neuroactive metabolite of tryptophan, attenuated the most stable effect of anxiogens in this model of anxiety--a decrease in the rate of leanings-out of the dark compartment --induced by caffeine, pentylenetetrazole and yohimbine, but not by beta-phenylethylamine (PEA). KYNA by itself did not alter behavior of mice in the chamber, in contrast to what has been observed in an elevated plus-maze, another model of anxiety, where KYNA had an anxiolytic pharmacological profile.

Fast confocal imaging of calcium released from stores in dendritic spines

The emerging significance of calcium stores in neuronal plasticity and the assumed involvement of dendritic spines in long-term plastic properties of neurons have led us to examine the presence and possible regulation of calcium stores in dendritic spines. Immunohistochemical staining for ryanodine receptors was found in dendritic spines of cultured hippocampal neurons. Confocal microscopic imaging of calcium transients in dendritic spines of these neurons in response to caffeine allowed us to demonstrate an independent and unique calcium store in spines. The response to caffeine was blocked by thapsigargin and ryanodine, and maintained in calcium-free medium. The calcium stores were depleted faster in the spines than the dendrites. Furthermore, when calcium was released from stores under calcium-free conditions, and diffused passively between the spine and the dendrite, the length of the spine neck determined the degree of spine independence. Finally, the caffeine-sensitive ryanodine receptor-linked calcium store was instrumental in regulating the response of neurons to glutamate. These results have important implications for understanding the roles of dendritic spines in neuronal integration and plasticity.

Bethanechol activates a post-receptor negative feedback mechanism in rabbit urinary bladder smooth muscle

PURPOSE

Recent studies using vascular and gut smooth muscles indicate that contractile receptor agonists may activate post-receptor down-regulatory mechanisms causing a temporary reduction in the strength of subsequent contractions. Our data indicate a similar mechanism exists in detrusor smooth muscle of the urinary bladder.

MATERIALS AND METHODS

Each isolated strip of female rabbit detrusor was placed in a tissue bath, secured to an isometric force transducer, and length-adjusted until depolarization with 110 mM KCl produced a maximum contraction (S0). Subsequent contractions were normalized to S0 (S/S0) or to a first stimulus with 30 mM KCl or caffeine (S/S1). Tissues were pretreated with the muscarinic receptor agonist, bethanechol (BE), then stimulated with KCl, caffeine, or Bay k 8644 to identify potential post-receptor down-regulation.

RESULTS

Contractions induced by 30 mM KCl had three phases labeled fast peak (FP), slow peak (SP) and steady-state (SS). In tissues exposed for 30 min. to a maximum BE concentration then washed for 5 min., the KCl-induced FP and SP, but not SS, responses were reduced by approximately 40%. Smaller reductions in peak KCl-induced contractions occurred in tissues pretreated for a shorter duration or with a 100-fold lower BE concentration. This down-regulation induced by bethanechol pretreatment was reversible, lasting approximately 1-2 h. Not only were KCl-induced contractions reduced by BE pretreatment, but also those produced by the intracellular Ca(2+)-mobilizer, caffeine, and the L-type Ca2+ channel agonist, Bay k 8644.

CONCLUSIONS

Pretreatment of isolated strips of rabbit detrusor with a muscarinic receptor agonist produced short-term down-regulation of KCl-induced peak contractions that may have involved inhibition of both influx of extracellular Ca2+ and release of intracellular Ca2+. Reductions in the degree of this novel modulatory response during disease conditions and aging could enhance contractile activity, possibly causing detrusor instability.

Caffeine and ryanodine may act on the plasma membrane of the circular muscle at the flexure region in the guinea-pig colon

The actions of caffeine and ryanodine on the spontaneous rhythmic activities in the guinea-pig colon were studied by mechanical tension recording. Caffeine reduced the amplitude of the spontaneous rhythmic activity at low concentration (0.3 mM-1 mM). At high concentration (3-10 mM), it induced a phasic transient contraction. The spontaneous rhythmic activity and a phasic contraction induced by caffeine, were blocked by verapamil (3 microM) or by removal of external Ca2+. Ryanodine affected neither resting tension nor frequency of spontaneous activity at 1 microM. However in the circular muscle strips pretreated with ryanodine, a sustained contraction was initiated after the removal of caffeine (10 mM). Continuous Ca2+ influx was necessary for spontaneous rhythmic activities and a phasic transient contraction, because it was abolished completely by the removal of external Ca2+, Verapamil (3 microM), a voltage gated L-type Ca2+ channels blocker, inhibited the spontaneous rhythmic activities and also inhibited phasic transit contraction followed by a sustained contraction induced by 10 mM caffeine. Our results suggest that caffeine may produce a sustained contraction by activating verapamil sensitive Ca2+ channel. In the muscle pretreated with both caffeine and ryanodine, continuous Ca2+ influx may occur also through verapamil sensitive pathway.

Caffeine induces central cholinergic analgesia

The antinociceptive effect of caffeine was examined by using the hot-plate, abdominal constriction tests in mice and the tail flick and paw-pressure tests in rats. Caffeine (1-5 mg kg-1 s.c. in mice; 2.5-5 mg kg-1 i.p. in rats) produced significant antinociception in both species which was prevented by atropine (5 mg kg-1 i.p.), pirenzepine (0.1 microgram per mouse i.c.v.), hemicholinium-3 (1 microgram/ mouse i.c.v.) and N6-cyclopentyladenosine (5 micrograms/mouse i.c.v.), but not by naloxone (1 mg kg-1 i.p.), CGP 35348 (100 mg kg-1 i.p.), alpha-methyl p-tyrosine (100 mg kg-1 i.p.) and reserpine (2 mg kg-1 i.p.). Intracerebroventricular injection of caffeine in mice at doses (2.5-5 micrograms per mouse) which were largely ineffective by parenteral routes, induces an antinociception whose intensity equalled that obtainable s.c. or i.p. In the antinociceptive dose-range, caffeine did not produce any behavioural impairment as revealed by the rotarod and Irwing tests. On the basis of the above data, it can be postulated that caffeine exerts an antinociceptive effect mediated by central amplification of cholinergic transmission.

Anxiogenic action of caffeine: an experimental study in rats

The anxiogenic action of caffeine (10, 25 and 50 mg/kg, i.p.) was investigated in rats and compared with that of yohimbine (2 mg/kg, i.p.). The experimental methods used were the open-field, elevated plus-maze, social interaction and novelty-suppressed feeding latency tests. Caffeine produced a dose-related profile of behavioural changes, which were qualitatively similar to those induced by yohimbine and which indicate an anxiogenic activity in rodents. Thus, both the drugs reduced ambulation and rears, and increased immobility and defaecation in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated-plus maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48-h food-deprived rats. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of caffeine and yohimbine. Subchronic administration of caffeine (50 mg/kg, i.p.) for 21 days, in different groups of animals, induced a significant degree of tolerance in the elevated plus-maze test, which was statistically significant after 14 and 21 days' treatment. Yohimbine, however, did not induce similar tolerance. When caffeine (50 mg/kg, i.p.) was withdrawn after 21 days' administration, to a separate group of rats, significant withdrawal anxiety was observed 48 h later as noted in the elevated plus-maze test. The investigations support clinical evidence of caffeine-induced anxiety, tolerance to anxiety on continued use, and withdrawal anxiety in chronic caffeine-containing beverage users.

Functional antagonism of the caffeine-discriminative stimulus by triazolam in humans

Six healthy male volunteers (aged 21-31 yr) were trained to discriminate between the methylxanthine caffeine (320 mg/70 kg, p.o.; e.g. drug A) and placebo (drug B). Then dose-effect curves were determined for triazolam (0.1-0.56 mg/70 kg), alone and in combination with the caffeine training dose (n = 6), buspirone (1.0-32.0 mg/70 kg), alone and in combination with the caffeine training dose (n = 4), and caffeine (56-560 mg/70 kg), alone and in combination with a selected dose of triazolam (n = 5). Triazolam blocked the discriminative effects of the caffeine training dose in a dose-related manner in five out of six subjects; whereas buspirone did so in only one out of four subjects. Different doses of caffeine alone generally produced dose-related increases in caffeine-appropriate responding; when administered concomitantly with triazolam, the caffeine dose-effect curve shifted significantly to the right. Triazolam and caffeine, but not buspirone and caffeine, generally produced significant interactions on several self-report and psychomotor performance measures. These results indicate that, at the doses tested, the caffeine discriminative stimulus can be blocked, at least partly by triazolam, but not by buspirone, which is consistent with the pharmacological actions of these compounds.

Effect of propofol on isolated human omental arteries and veins

To elucidate the effect and mode of action of propofol on human vascular smooth muscle tension, we have investigated the effect of propofol alone and the effect of propofol on contractions induced by U46619, KCl and caffeine on isolated human omental vessels. Propofol 10(-3) mol litre-1 induced contractions in both arteries and veins attenuated the contraction elicited by U46619, KCl and caffeine in a concentration-dependent manner. The threshold concentrations for the effect of propofol in the artery were: 10(-5) mol litre-1 (U46619, caffeine) and 10(-4) mol litre-1 (KCl); and in the vein, 10(-5) mol litre-1 (U46619) and 10(-4) mol litre-1 (KCl, caffeine). We conclude that propofol at lower concentrations appeared to primarily attenuate contraction involving release of cellularly sequestered calcium. At higher concentrations (> 10(-4.5) mol litre-1), propofol appeared to affect contraction involving extracellular or intracellular calcium fluxes similarly.

Effects of 8-(N-N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) on skinned myocardial fibres of the rat: reversible inhibition of calcium release from the sarcoplasmic reticulum

The effects of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-3), which is reported to inhibit the release of intracellularly stored Ca2+ in skeletal and smooth muscles, were examined in ventricular myocardia of the adult rat. In skinned papillary muscle fibres with functional sarcoplasmic reticulum (SR) preserved, application of 100 or 300 microM TMB-8 during the Ca2+ loading period had no significant effect on the peak tension of subsequent caffeine-induced contraction, but when applied during exposure to caffeine, concentration-dependent reduction of the peak tension was observed. At 1000 microM, TMB-8 reduced the peak tension of caffeine-induced contraction when applied either during Ca2+ loading or during exposure to caffeine. TMB-8 had no substantial influence on the Ca(2+)-tension of skinned fibres without functional SR. In isolated papillary muscle preparations, TMB-8 prolonged the action potential duration and decreased the maximum rate of rise of potential, leading to abolition of contraction at 100 microM. In conclusion, TMB-8 may be a useful pharmacological tool for inhibiting Ca2+ release from SR, but only in skinned myocardial preparations.

Caffeine and cocaine interaction on memory consolidation in mice

The main aim of this study was to investigate the interaction between the effects of caffeine and cocaine on memory consolidation in mice. For this purpose, CD1 mice were used; they were injected intraperitoneally and tested in a one-trial inhibitory avoidance task. The apparatus consisted of two compartments, one lighted and the other in darkness. On the training day, the animal had to go from the lighted to the dark compartment, where it received an electric shock. On the test day, carried out in our experiments 24 hours later, the time the animal waited to enter the dark compartment is the measure of its retention (for further details, see Methods). Three sets of experiments were carried out. In a first set, immediately posttraining, caffeine (0.25, 0.5 and 1 mg/kg) or cocaine (1, 2.5 and 5 mg/kg) administrations enhanced the memory consolidation of mice. In a second set, the D2 dopamine receptor antagonist, (-)-sulpiride, antagonized the enhancing effect of caffeine on memory. In a third set, a clear interaction between caffeine and cocaine was evident. The results are interpreted in terms of interaction of the drugs used with the dopaminergic system.

Assessment of the time course of drugs with inhibitory effects on hepatic metabolic activity using successive salivary caffeine tests

In clinical practice is very important to know the time course of the inhibitory effects of drugs to avoid side effects when several agents are taken concomitantly. We attempted to validate the effectiveness of successive salivary caffeine tests establishing the time for cimetidine to inhibit hepatic metabolism. The time of cimetidine's inhibitory effect as reported in other studies was chosen as the reference. In this open-label, prospective longitudinal, 16-day study, five healthy volunteers were treated with cimetidine 1 g/day for 5 days. After the intake of caffeine 300 mg, salivary caffeine tests were carried out on days -1 (control value), 1, 4, 8, 12, and 16. The mean systemic caffeine clearance was decreased after 24 hours of cimetidine. The drug's maximum inhibitory effect was reached after 5 days of administration, returning to previous values progressively 1-7 days after discontinuing cimetidine. No change occurred in the apparent volume of distribution. The time course of cimetidine's inhibitory effect was similar to that described with other methodologies. Although this was a pilot trial and the results have to be confirmed, it seems that successive salivary caffeine measurements could be a safe, reliable, noninvasive test for exploring the time course of the inhibitory effects of drugs on hepatic metabolism.

Anxiolytic activity of adenosine receptor activation in mice

1. Purine analogues have been examined for anxiolytic- and anxiogenic-like activity in mice, by use of the elevated plus-maze. 2. The selective A1 receptor agonist, N6-cyclopentyladenosine (CPA) had marked anxiolytic-like activity at 10 and 50 microg kg(-1), with no effect on locomotor performance at these doses. 3. The A1 selective adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (CPX) had no significant effect on anxiety-related measures or locomotor behaviour, but blocked the anxiolytic-like activity of CPA. The hydrophilic xanthine, 8-(p-sulphophenyl) theophylline did not prevent anxiolysis by CPA. 4. Caffeine had anxiogenic-like activity at 30 mg kg(-1) which was prevented by CPA at 50 micro kg(-1). 5. The A2 receptor agonist, N6-[2-(3,5-dimethoxyphenyl)-2(2-methylphenyl)-ethyl]adenosine (DPMA) had no effect on anxiety behaviour but depressed locomotor activity at the highest dose tested of 1 mg kg(-1). The A2 receptor antagonist, 1,3-dimethyl-l-propargylxanthine (DMPX) had no effect on anxiety-related measures or locomotion and did not modify the anxiolytic-like activity of CPA. 6. Administration of DPMA in combination with anxiolytic doses of CPA prevented the anxiolytic-like activity of the latter. 7. The results suggest that the selective activation of central A1 adenosine receptors induces anxiolytic-like behaviour, while the activation of A2 sites causes locomotor depression and reduces the effects of A1 receptor activation. The absence of any effect of CPX alone suggests that the receptors involved in modulating behaviour in the elevated plus-maze in mice are not activated tonically by endogenous adenosine.

Metabolic and hormone-related responses to caffeine in rats

The time course of effects of caffeine on plasma glucose and non-esterified fatty acids (NEFA) were measured and related to various hormonal responses associated with substrate mobilization and utilization. Participation of the sympatho-adrenal system (SAS) in the metabolic and hormonal actions of caffeine was also investigated by the use of ganglionic blockade. Following 50 mg kg-1 i.p. injections of caffeine in rats, plasma glucose increased 25% and NEFA 40%, and these actions were parallelled by an elevation of plasma insulin, ACTH and corticosterone, without changes in glucagon. It is suggested that the insulin response is related to the plasma glucose increase and possibly also to an action of cAMP. When caffeine was injected in rats previously treated with the ganglionic blocker, hexamethonium, none of the responses mentioned above were modified. These results show that the glucose and NEFA responses are independent of glucagon secretion and are due not only to SAS activation but also to other mechanisms such as the increased ACTH and corticosterone secretion. It is also suggested that the mobilization of substrates by caffeine is mediated, through these various mechanisms, by the activation of cAMP and by phosphodiesterase inhibition.

Ryanodine receptor-mediated intracellular calcium release in rat cerebellar Purkinje neurones

1. Ryanodine receptor-mediated Ca2+ release was investigated in Purkinje neurones of rat cerebellar slices by using whole-cell patch-clamp recordings combined with fluorometric digital imaging of cytoplasmic Ca2+ concentration ([Ca2+]i). 2. Caffeine caused a transient increase in [Ca2+]i in the somata and dendrites of Purkinje neurones. Caffeine-induced Ca2+ transients were not associated with a membrane inward current and persisted in Ca(2+)-free external solutions, indicating that they are caused by Ca2+ released from intracellular stores. The amplitudes of the caffeine-mediated elevations in [Ca2+]i were strongly dependent on the baseline level of [Ca2+]i. 3. Intracellular application of Ruthenium Red through the patch pipette blocked caffeine-induced Ca2+ transients in Purkinje neurones. Ryanodine when applied either intra- or extracellularly caused a use-dependent block of caffeine-induced Ca2+ release. 4. Depolarization-induced Ca2+ transients were strongly prolonged by caffeine. Several lines of evidence suggest that these prolongations reflect Ca(2+)-induced Ca2+ release. 5. Despite the presence of skeletal muscle type ryanodine receptors in Purkinje neurones, depolarizing pulses failed to induce any changes in [Ca2+]i when the influx of Ca2+ through voltage-gated channels was prevented by using Ca(2+)-free solution, or when applying blockers of voltage-gated Ca2+ channels. 6. Dendritic Ca2+ transients produced by stimulation of the excitatory climbing fibre synaptic input were also prolonged by caffeine, indicating that ryanodine receptor-mediated release of Ca2+ may be involved in synaptic signalling in cerebellar Purkinje neurones. 7. Ryanodine receptor-mediated release of Ca2+ in cerebellar Purkinje neurones can be explained by a model in which release of Ca2+ is strongly facilitated by the co-operative action of Ca2+, caffeine and/or ryanodine. Our results suggest that Ca2+ release in these central neurones becomes prominent only during episodes of intensive electrical activity associated with increased Ca2+ entry.

Modulation of the ryanodine receptor sarcoplasmic reticular Ca2+ channel in skinned fibers of fast- and slow-twitch skeletal muscles from rabbits

This study was performed to compare skinned fibers from rabbit adductor magnus (AM) and soleus (SL) muscles with regard to the influence of caffeine, Ca2+ and Mg2+ on the depressive effects of ryanodine (RYA) on the caffeine-induced tension transients. Single skinned fibers were immersed in solutions to load Ca2+ into, and release Ca2+ from the SR (a load-release cycle). Three cycles were sequentially performed in each skinned fiber: (1) a control (no RYA), (2) a conditioning period in which activation was carried out in the presence of ryanodine plus various concentrations of the modulators, i.e. caffeine, Ca2+ or Mg2+, and (3) a test (no RYA) which monitored the release activity retained after the conditioning cycle. The depressive effect of RYA was found to be a function of [ryanodine], [caffeine], or [Ca2+], and an inverse function of [Mg2+], where [] denotes concentration. The half-maximal effects of RYA in AM (5 microM RYA) and SL (10 microM RYA), respectively, occurred at a pCa50 of 5.32 versus 5.43 without caffeine, or pCa50 of 7.24 versus 6.88 and pMg50 of 3.29 versus 3.61 with 25 mM caffeine, at a [caffeine] of 4.96 versus 7.29 mM, and at a [ryanodine] of 31.0 versus 101.6 microM. Thus, the RYA depression in skinned muscle fibers is modulated by caffeine, Ca2+, and Mg2+ in both muscle types, and AM is at least two- to fourfold more sensitive than SL.

Involvement of dihydropyridine receptors in terminating Ca2+ release in rat skeletal myotubes

1. Combined patch-clamp and fura-2 measurements were performed in order to investigate the effect of dihydropyridine (DHP) antagonists on termination of sarcoplasmic reticulum (SR) Ca2+ release in cultured rat skeletal myoballs. 2. Ca2+ transients induced by 10 mM caffeine were curtailed by depolarization (e.g. +20 mV for 1 s) and subsequent repolarization (-70 mV). This phenomenon is termed RISC (repolarization-induced stop of caffeine-induced Ca2+ release). 3. At 0.5 to 1 microM, DHP antagonists (nifedipine or (+)PN200-110) strongly inhibited RISC and also slowed the decay of intracellular Ca2+ concentration ([Ca2+]i) following repolarization after depolarization-induced Ca2+ release (-20 or -10 mV for 5 s). 4. The activation time course of the Ca2+ channel associated with the DHP receptor (DHPR) was investigated by measuring DHP-sensitive Ca2+ channel tail currents, while varying the duration of depolarizing pulses. The tail currents increased with pulse duration and peaked around 0.7, 0.9 and 1.1 s for depolarizations to +70, +40 and +20 mV, respectively. These values are compatible with the activation time course of RISC (0.5-1 s to maximally activate RISC at +20 to +60 mV). 5. These results suggest that the DHPR in T-tubular membranes regulates closing of the ryanodine receptor (RyR)-Ca2+ release channel complex through membrane potential change.

Inhibition of norepinephrine and caffeine-induced activation by ryanodine and thapsigargin in rat mesenteric arteries

We examined the effects of ryanodine and thapsigargin on changes in cytoplasmic [Ca2+] (Cai) and muscle tension in rat mesenteric resistance arteries induced by norepinephrine (NE) and caffeine. Both ryanodine and thapsigargin markedly inhibited the increase in Cai and contractile responses to caffeine in physiological saline and to NE and caffeine in calcium-free conditions. In contrast, peak responses to potassium depolarisation and NE in physiological saline appeared little affected, although time taken to achieve 50% of peak response after addition of NE was slowed after ryanodine and thapsigargin treatment. Neither ryanodine nor thapsigargin altered resting tone or Cai or the Ca2+ sensitivity of contraction under depolarized conditions. The NE concentration-response relationship was not significantly altered after ryanodine or thapsigargin. Ryanodine and thapsigargin inhibit the release of intracellular Ca2+ stores by NE and caffeine. Inhibition of release of intracellular Ca2+ by NE has only slight effects on contractile responses of mesenteric resistance arteries when extracellular Ca2+ is present.

Endothelium-independent vasoconstricting and vasodilating actions of halothane on rat mesenteric resistance blood vessels

BACKGROUND

Whether volatile anesthetics produce changes in vascular resistance and blood flow because of direct effects on vascular tissue is unclear. Direct vasoconstricting and vasodilating actions have been demonstrated in isolated conductance arteries in vitro, but there is little information regarding direct effects on the small vessels that mediate resistance and flow changes in vivo.

METHODS

We investigated the actions of halothane on 50-200 microM branches of the rat mesenteric artery that were cannulated and studied in vitro. The vessels were pressurized to 60 mmHg, and vascular dimensions were continuously monitored using a computer-based real-time image analysis system. The vessel bath was perfused with HCO3(-)-buffered saline (37 degrees C) equilibrated with 95% O2/5% CO2 (+/- halothane). The vascular endothelium was mechanically removed before cannulation in some vessels.

RESULTS

In unstimulated vessels, halothane had a concentration-dependent vasoconstricting action (EC50 = 0.45 mM approximately 1.5 vol% at 37 degrees C) that was largely transient and was similar to that produced by caffeine. Both halothane and caffeine constrictions were unaffected by bath [Ca2+], nifedipine (1 microM) or Cd2+ (100 microM) and were abolished by ryanodine (10 microM). In addition, caffeine responses were attenuated by halothane in a concentration-dependent manner (EC50 = 1.6 mM). In vessels preconstricted with KCl (40 mM) or phenylephrine (10(-6) M), halothane produced transient constriction followed by concentration-dependent vasodilation. Ryanodine, which abolished halothane constrictions, had little effect on the amplitude of KCl- or phenylephrine-induced constrictions or the vasodilating action of halothane. Removal of the endothelium likewise had little effect on the vasoconstricting or the vasodilating actions of halothane in unstimulated, KCl- or phenylephrine-constricted vessels. Halothane completely relaxed KCl and phenylephrine constrictions with EC50 values of 0.36 mM (1.2% at 37 degrees C) and 0.75 mM (2.5%), respectively, in intact vessels before ryanodine; 0.25 mM (0.8%) and 0.59 mM (1.9%) in intact vessels after ryanodine; and 0.52 mM (1.7%) and 0.67 mM (2.2%) in endothelium-denuded vessels.

CONCLUSIONS

Halothane has endothelium-independent vasoconstricting and vasodilating actions in isolated mesenteric resistance blood vessels. The vasoconstricting action appears to involve halothane-induced Ca2+ release from caffeine/ryanodine-sensitive intracellular store(s). The vasodilating action in phenylephrine- or KC1-constricted vessels is independent of the Ca(2+)-releasing action and most likely involves an effect(s) on sarcolemmal-dependent Ca2+ signaling (e.g., extracellular Ca2+ influx) and/or Ca2+ activation of contractile proteins. The magnitude of both the vasoconstricting and the vasodilating actions of halothane in these vessels at clinically relevant concentrations suggests these direct actions contribute to the overall cardiovascular effects of halothane in vivo.

Ca2+ release induced by myotoxin alpha, a radio-labellable probe having novel Ca2+ release properties in sarcoplasmic reticulum

1. Myotoxin alpha (MYTX), a polypeptide toxin purified from the venom of prairie rattlesnakes (Crotalus viridis viridis) induced Ca2+ release from the heavy fraction (HSR) but not the light fraction of skeletal sarcoplasmic reticulum at concentrations higher than 1 microM, followed by spontaneous Ca2+ reuptake by measuring extravesicular Ca2+ concentrations using the Ca2+ electrode. 2. The rate of 45Ca2+ release from HSR vesicles was markedly accelerated by MYTX in a concentration-dependent manner in the range of concentrations between 30 nM and 10 microM, indicating the most potent Ca2+ releaser in HSR. 3. The Ca2+ dependency of MYTX-induced 45Ca2+ release has a bell-shaped profile but it was quite different from that of caffeine, an inducer of Ca(2+)-induced Ca2+ release. 4. 45Ca2+ release induced by MYTX was remarkable in the range of pCa between 8 and 3, whereas that by caffeine was prominent in the range of pCa, i.e., between 7 and 5.5. 5. MYTX-induced 45Ca2+ release consists of both early and late components. The early component caused by MYTX at low concentrations (30-300 nM) completed within 20 s, while the late component induced by it at higher concentrations (> 0.3 microM) was maintained for at least 1 min. 6. Both the components were almost completely inhibited by inhibitors of Ca2+ such as Mg2+, ruthenium red and spermine. 7. 45Ca2+ release induced by caffeine or beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) was completely inhibited by high concentrations of procaine. Procaine abolished the early component but not the late one, suggesting that at least the early component is mediated through Ca(2+)-induced Ca2+ release channels. 8. On the basis of these results, the character of Ca2+ release induced by MYTX was quite different from that caused by caffeine or AMP-PCP, suggesting that MYTX induces Ca2+ release having novel properties in HSR. MYTX is the first polypeptide Ca2+ inducer and has become a useful pharmacological tool for clarifying the mechanism of Ca2+ release from skeletal muscle SR.

Caffeine-induced hypercalciuria and renal prostaglandins: effect of aspirin and n-3 polyunsaturated fatty acids

Effects of aspirin and fish-oil ingestion on caffeine-induced hypercalciuria and renal prostaglandins (PG) were investigated in 12 healthy women. The 11-wk study consisted of 7-d baseline, 5-d aspirin (1000 mg/d), 11-d washout, and two 24-d fish-oil periods (FO-1 and FO-2, respectively, providing 1.5 vs 3.0 g n-3 fatty acids/d) separated by a 4-d washout period. Caffeine-load (CL) tests providing 5 mg caffeine/kg body wt were administered after baseline and each experimental period. Timed urine samples were collected precaffeine (basal) and at 1, 2, and 3 h post-caffeine. PGE2 excretion decreased during tests after aspirin and FO-2. There were significant increases in PGF2 alpha from baseline during each CL test. Hypercalciuria was observed during each CL test and the magnitude of this response was not altered by the experimental treatments. The finding that concentrations of post-caffeine urinary PGF2 alpha paralleled concentrations of urinary calcium supports the possibility that this prostaglandin plays a role in caffeine-induced hypercalciuria.

The effect of caffeine on prostaglandin output from the guinea-pig uterus

1. Caffeine increased the outputs of prostaglandin F2 alpha (PGF2 alpha), PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus on days 7 and 15 of the oestrous cycle. The effect on PGE2 output depended on the age of the animals and was absent in younger guinea-pigs (< 4 months). Theophylline also stimulated the outputs of PGF2 alpha and 6-keto-PGF1 alpha, but not the output of PGE2, from the day 7 guinea-pig uterus. 2. The stimulatory effects of caffeine on the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus were not prevented by lack of extracellular calcium, ryanodine or ruthenium red (both inhibitors of calcium release via the ryanodine receptor), although the increase in PGF2 alpha output tended to be slower when extracellular calcium was absent. Also, ryanodine flattened and broadened the peak of increased PGF2 alpha release. 3. The calmodulin antagonists, W-7 and trifluoperazine, had no inhibitory effect on the caffeine-stimulated increases in uterine prostaglandin output. In fact, W-7 (but not trifluoperazine) greatly potentiated the action of caffeine on uterine PGF2 alpha output, but had little or no potentiating effect on the action of caffeine on uterine PGE2 and 6-keto-PGF1 alpha outputs. 4. TMB-8, an intracellular calcium antagonist, inhibited the increase in PGF2 alpha output produced by caffeine without preventing the increases in outputs of PGE2 and 6-keto-PGF1 alpha. 5. These studies suggest that caffeine stimulates uterine PGF2 alpha synthesis and release by a mechanism dependent upon intracellular calcium, but this mechanism is not mediated by activation of any of the three well-characterized ryanodine receptors or by calmodulin. Furthermore, the increases in the synthesis and release of PGE2 and 6-keto-PGFI alpha. in the guinea-pig uterus induced by caffeine appear to involve mechanism(s) different from that which stimulates PGF2 alpha production.

Action of niflumic acid on evoked and spontaneous calcium-activated chloride and potassium currents in smooth muscle cells from rabbit portal vein

1. The action of niflumic acid was studied on spontaneous and evoked calcium-activated chloride (ICl(Ca)) and potassium (IK(Ca)) currents in rabbit isolated portal vein cells. 2. With the nystatin perforated patch technique in potassium-containing solutions at a holding potential of -77 mV (the potassium equilibrium potential), niflumic acid produced a concentration-dependent inhibition of spontaneous transient inward current (STIC, calcium-activated chloride current) amplitude. The concentration to reduce the STIC amplitude by 50% (IC50) was 3.6 x 10(-6) M. 3. At -77 mV holding potential, niflumic acid converted the STIC decay from a single exponential to 2 exponential components. In niflumic acid the fast component of decay was faster, and the slow component was slower than the control decay time constant. Increasing the concentration of niflumic acid enhanced the decay rate of the fast component and reduced the decay rate of the slow component. 4. The effect of niflumic acid on STIC amplitude was voltage-dependent and at -50 and +50 mV the IC50 values were 2.3 x 10(-6) M and 1.1 x 10(-6) M respectively (cf. 3.6 x 10(-6) M at -77 mV). 5. In K-free solutions at potentials of -50 mV and +50 mV, niflumic acid did not induce a dual exponential STIC decay but just increased the decay time constant at both potentials in a concentration-dependent manner. 6. Niflumic acid, in concentrations up to 5 x 10(-5) M, had no effect on spontaneous calcium-activated potassium currents. 7. Niflumic acid inhibited noradrenaline- and caffeine-evoked IO(Ca) with an ICM50 of 6.6 x 10-6 M, i.e.was less potent against evoked currents compared to spontaneous currents. In contrast niflumic acid(2 x 10-6 M-5 x 105 M) increased noradrenaline- and caffeine-induced IK(ca).8. The results are discussed with respect to the mechanism of block of ICl(Ca) by niflumic acid and its suitability as a pharmacological tool for assessing the role of Ic(ca) in physiological mechanisms.

Influence of the absolute configuration on the vascular effects of tetrandrine and isotetrandrine in rat aorta

The relaxant action of (1S, 1'S) tetrandrine and its isomer (1R, 1'S) isotetrandrine were examined in rat aortic strips, in presence or absence of extracellular calcium. Both alkaloids relax, concentration dependently, the contractile response elicited by depolarizing solution (KCl 80 mM) or noradrenaline (1 microM). Tetrandrine, however, showed a selectivity of action towards the KCl-induced contraction while isotetrandrine did not. In Ca(2+)-free solution, both alkaloids inhibited the contraction induced by noradrenaline, but they did not affect the transient contraction due to caffeine then this effect is not attributable to direct inhibition of the smooth muscle contractile elements. The refilling of intracellular calcium stores sensitive to noradrenaline or caffeine was significantly inhibited by both alkaloids.

Modulation of Ca2+ release in cultured neonatal rat cardiac myocytes. Insight from subcellular release patterns revealed by confocal microscopy

It is well established that in heart muscle the influx of Ca2+ through Ca2+ channels during the action potential is the main trigger for Ca2+ release from the sarcoplasmic reticulum (SR), but intact cardiac tissue and single myocytes are also known to exhibit spontaneous Ca2+ release from the SR under a variety of circumstances. Although conditions favoring spontaneous activity have been examined extensively, mechanisms modulating or regulating spontaneous as well as triggered Ca2+ release are still largely unknown. Using the high spatial and temporal resolution of laser-scanning confocal microscopy, we investigated subcellular aspects of spontaneous and triggered Ca2+ release in isolated rat neonatal myocytes loaded with the Ca(2+)-sensitive fluorescent dye fluo 3. Three distinct patterns of spontaneous Ca2+ release were identified: (1) a homogeneous Ca2+ release, presumably corresponding to Ca2+ release during a spontaneous action potential, (2) a focal or spatially restricted Ca2+ release with no or only limited subcellular propagation, and (3) a Ca2+ release propagating as a wave throughout the entire cell. Pharmacologic tools that interfere with the SR revealed that all release types were critically dependent on the Ca2+ release and uptake function of the SR. From our results we conclude that the probability, extent, and pattern of Ca2+ release are modulated on the subcellular level. The observed spectrum of release patterns can be explained by a space- and time-dependent variability in the positive feedback of the Ca(2+)-induced Ca(2+)-release mechanism within an individual myocyte. Presumably, this variability depends on the existence of subcellular functional elements of the SR. The actual degree of positive feedback may be modulated locally by the Ca(2+)-loading state of each SR element.