Potentiating Effect Of Caffeine Research Articles

Anesthetics and Cell-Cell Communication: Potential Ca2+-Calmodulin Role in Gap Junction Channel Gating by Heptanol, Halothane and Isoflurane.

Cell–cell communication via gap junction channels is known to be inhibited by the anesthetics heptanol, halothane and isoflurane; however, despite numerous studies, the mechanism of gap junction channel gating by anesthetics is still poorly understood. In the early nineties, we reported that gating by anesthetics is strongly potentiated by caffeine and theophylline and inhibited by 4-Aminopyridine. Neither Ca2+ channel blockers nor 3-isobutyl-1-methylxanthine (IBMX), forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester or H7 had significant effects on gating by anesthetics. In our publication, we concluded that neither cytosolic Ca2+i nor pHi were involved, and suggested a direct effect of anesthetics on gap junction channel proteins. However, while a direct effect cannot be excluded, based on the potentiating effect of caffeine and theophylline added to anesthetics and data published over the past three decades, we are now reconsidering our earlier interpretation and propose an alternative hypothesis that uncoupling by heptanol, halothane and isoflurane may actually result from a rise in cytosolic Ca2+ concentration ([Ca2+]i) and consequential activation of calmodulin linked to gap junction proteins.

Adenosine A1 Receptor-Mediated Synaptic Depression in the Developing Hippocampal Area CA2

Immunolabeling for adenosine A1 receptors (A1Rs) is high in hippocampal area CA2 in adult rats, and the potentiating effects of caffeine or other A1R-selective antagonists on synaptic responses are particularly robust at Schaffer collateral synapses in CA2. Interestingly, the pronounced staining for A1Rs in CA2 is not apparent until rats are 4 weeks old, suggesting that developmental changes other than receptor distribution underlie the sensitivity of CA2 synapses to A1R antagonists in young animals. To evaluate the role of A1R-mediated postsynaptic signals at these synapses, we tested whether A1R agonists regulate synaptic transmission at Schaffer collateral inputs to CA2 and CA1. We found that the selective A1R agonist CCPA caused a lasting depression of synaptic responses in both CA2 and CA1 neurons in slices obtained from juvenile rats (P14), but that the effect was observed only in CA2 in slices prepared from adult animals (~P70). Interestingly, blocking phosphodiesterase activity with rolipram inhibited the CCPA-induced depression in CA1, but not in CA2, indicative of robust phosphodiesterase activity in CA1 neurons. Likewise, synaptic responses in CA2 and CA1 differed in their sensitivity to the adenylyl cyclase activator, forskolin, in that it increased synaptic transmission in CA2, but had little effect in CA1. These findings suggest that the A1R-mediated synaptic depression tracks the postnatal development of immunolabeling for A1Rs and that the enhanced sensitivity to antagonists in CA2 at young ages is likely due to robust adenylyl cyclase activity and weak phosphodiesterase activity rather than to enrichment of A1Rs.

Autophagy inhibition by caffeine increases toxicity of methamphetamine in SH-SY5Y neuroblastoma cell line.

Methamphetamine (METH) is a highly addictive CNS stimulant that its long-term use is associated with the loss of neurons in substantia nigra and development of Parkinson's disease later in life. Common form of METH is Ya-Ba tablet, in which, large portion of caffeine is added to the mass to enhance the stimulatory effect. Previous study demonstrated that caffeine potentiates the toxic effect of METH in association with the production of reactive oxygen species and the induction of apoptosis. Since METH causes induction of autophagy, the question was raised whether this pathway participates in the potentiating effect of caffeine on METH neurotoxicity. We used SH-SY5Y, a neuroblastoma cell line, as an in vitro model to study the effect of METH and caffeine. Co-treatment of non-toxic concentrations of METH, at 0.5 mM, and caffeine, at 1 mM, caused reduction of the cell viability. Reduction of the cell viability was associated with attenuation of autophagy, demonstrated by reduction of LC3-II levels and the number of autophagosome puncta, together with increase of caspase-3 activation. Similar effect was produced by treatment with autophagy inhibitors, 3-MA and wortmanin. Our results suggested that caffeine potentiates METH toxicity through inhibition of autophagy and that autophagy serves as a protective mechanism. In conclusion, we proposed the augmented hazard associated with caffeine and METH combination in Ya-Ba abusers.

Influence of Caffeine on Allyl Alcohol-Induced Hepatotoxicity in Rats* I. In Vivo Study

Cotreatment of rats with a low hepatotoxic dose (30.7 mg/kg, i.p.) of allyl alcohol (AA) and a higher, but nontoxic, dose (150 mg/kg, oral) of caffeine (CF) potentiated the hepatotoxicity of AA. This was verified by significantly higher levels of plasma alanine aminotransferase (ALT) activity and histopathologically greater severity of lesions in the periportal hepatocytes than those due to AA alone. Treatment of rats with 4-methylpyrazole (4-MP) (0.5 mmol/kg, i.p.) (an inhibitor liver alcohol dehydrogenase) for 30 minutes, followed by similar cotreatment with AA and CF, completely prevented the elevation of plasma levels of ALT and histological damage induced by cotreatment with CF and AA 24 hours following their administration. Severe liver damage induced by cotreatment with CF and AA was further, markedly enhanced by phenobarbital pretreatment (80 mg/kg, i.p., 3 days). Thus, extensive necrosis of periportal hepatocytes was noted, as well as edema and accumulation of inflammatory cells in the necrotic foci caused by such pretreatment. The depression of hepatic nonprotein sulfhydryls resulting from CF plus AA was much more severe than that caused by AA or CF alone and appeared as early as 30 minutes after administration. However, much less marked depletion of protein thiols was observed following similar treatments. Significant increase in lipid peroxidation (as measured by melondialdehyde [MDA] formation) was also observed in rat liver but only 24 hours after administration. The production ofMDA in the rat liver was significantly higher after administration of AA plus CF than after administration of AA alone. Pretreatment of rats with phenobarbital further significantly enhanced the formation of 2,4-dinitrophenylhydrazine (DNP)-reactive metabolite(s) (measured as DNP-acrolein adduct equivalents) in rat liver induced by AA (30.7 mg/kg) plus CF (150 mg/kg) within 1 hour following such treatment. Cotreatment with AA and a higher dose of CF resulted in significantly higher excretion of urinary thioethers or mercapturic acids than in rats treated with AA alone. Thus, these data suggest that an increased bioactivation pathway of acrolein involving a P450 mixed-function oxidase system caused by CF may be involved in such potentiating effects of CF on AA-induced hepatotoxicity in rats.

Caffeine potentiation of calcium release in frog skeletal muscle fibres.

The effects of caffeine at concentrations up to 3 mM were studied on Ca signals obtained using the metallochromic Ca indicator dyes Arsenazo III and Antipyrylazo III in cut frog skeletal muscle fibres mounted in a triple Vaseline-gap chamber and stimulated by voltage clamp or action potential. The peak amplitude of the transient absorbance change due to Ca2+ release following action potential stimulation is potentiated by an amount dependent on caffeine concentration up to 0.5 mM, and by a concentration-independent amount between 0.5 and 2 mM. At 3 mM-caffeine, the potentiation is reduced, and the Ca signal can have a smaller amplitude than under the control condition. The time course of the rising phase of the Ca signal is preserved by the potentiating effect of caffeine; however, the decay rate of the Ca signal is increasingly slowed at caffeine concentrations greater than 0.5 mM. No substantial change was found in the resting myoplasmic Ca2+ level at caffeine concentrations near 0.5 mM. Even if the free Ca2+ concentration in the presence of this level of caffeine were to increase by 0.04 microM (the threshold of detectability), the calculated potentiation of the Ca signal due to increased partial saturation of intracellular Ca2+ buffers would amount to only about 7%. This value is significantly less than the amount of potentiation observed (up to 40%) following action potentials at caffeine levels of 0.5 mM and above. Experiments made with the impermeant potentiometric dye NK2367 show no alteration by caffeine of the electrical properties of the tubular system. Caffeine at up to moderate concentrations causes a substantial increase in the maximal Ca2+ release obtained following large depolarizations. The voltage dependence of the Ca2+ release is characterized by a caffeine concentration-dependent shift towards more negative membrane potentials. The potentiation of Ca2+ release by caffeine was found to be independent of the external free Ca2+ level. The potentiation of the Ca2+ release process by caffeine is likely to occur at a step subsequent to the depolarization of the transverse tubule membrane, and suggests the presence of an intermediate step, or second messenger, in the excitation-contraction coupling process.

Effect of caffeine on intramembrane charge movement and calcium transients in cut skeletal muscle fibres of the frog.

1. The authors have studied the effect of caffeine in subthreshold concentration (0.5 mmol l(-1) at 2-4 degrees C) on the contraction threshold, on intramembrane charge movement and calcium transients in voltage-clamped frog skeletal muscle fibres.2. The single-gap technique (Kovács & Schneider, 1978) was used for the voltage clamping of terminated segments of cut fibres. Ionic conductances were minimized by using caesium glutamate at the open end pool and tetraethylammonium sulphate and tetrodotoxin at the closed end pool.3. Myoplasmic calcium transients evoked by depolarizing pulses were recorded by measuring the changes in absorbance of the fibres at 720 nm after the intracellular application of Antipyrylazo III dye.4. The strength-duration curve for contraction threshold was shifted towards more negative membrane potentials in the presence of caffeine. Shift was more definite at shorter pulse durations than at the rheobase.5. The total amount of charge moving during the depolarizing pulses at different membrane potentials was not changed by caffeine treatment, whereas the threshold amounts of charge moved during the critical periods of the contraction threshold decreased at different voltages (by about 23%).6. In the presence of caffeine, calcium transients accompanying long (100 ms) depolarizing pulses showed increased voltage-dependent peak amplitudes, rising phases and rate coefficients referring to calcium release, but a decreased voltage-dependent re-uptake rate either during or after the pulse.7. Calcium transients evoked by depolarizing pulses along the strength-duration curve for contraction threshold gave the same peak amplitudes (ranging from 0.9 to 2.8 mumol l(-1) free myoplasmic calcium on different fibres), but membrane-potential-dependent latency times and rising phases. The rate coefficients for declining phase did not depend on the preceding pulse voltage.8. On applying caffeine, the calcium transients related to the contraction threshold also had equal but smaller peak amplitudes, shorter latency times and the same magnitude of voltage-independent rate coefficients for the declining phase as in the control solution.9. The twitch potentiating effect of caffeine can be explained by its facilitating calcium release from the sarcoplasmic reticulum, while the re-uptake rate is not modified. The apparent inhibition of re-uptake can be related to the enhanced release of calcium due to caffeine effect. Due to the sensitizing effect of caffeine on the sarcoplasmic reticulum membrane, smaller amounts of charge are needed to reach the contraction threshold than without caffeine.

Cell killing by various nitrosoureas and the potentiating effect of caffeine

Cell killing by various nitrosoureas and the potentiating effect of caffeine on cell killing were quantified by means of colony-forming assays in a clonal derivative of M3-1 Chinese hamster cells. The dose-reponse relationships for ethylnitrosourea and 3 chloroethylnitrosourea derivatives were compared with tha of 1,3-bis(trans-4-hydroxycyclohexyl)-1-nitrosourea, which is a purely carbamoylating agent. The chloroethylnitrosoureas with both alkylating and carbamoylating activity ere the most toxic, followed by a chloroethylnitrosourea with alkylating activity alone and then by the purely carbamoylating agent. The least toxic agent was ehylnitrosourea, which has both alkylating and carbamoylating activity. Caffeine (when present through the entire period of colony growth) potentiated cell killing for all nitrosoureas with alkylating activity but had no influence on cell killing by the purely carbamoylating agent. Because carbamoylation occurs mainly with proteins, whereas nucleic acids as well as proteins are cellular targets for alkylation, it is concluded that potentiation of cell killing by caffeine is based on the reaction of a drug with the cellular DNA.

Nature of chromosome gaps induced by alkylating agents and γ-rays as revealed by caffeine treatment

Abstract In the cells of primary roots of Crepis capillaris, post-treatment with caffeine increased the frequency of gaps and chromosomal aberrations induced by the alkylating agents ethyleneimine and N-nitroso-N-methylurethane and γ-rays. The increase in the frequency of gaps was considerably lower than that observed in chromosomal aberrations, this being more strongly expressed in the case of the alkylating agents. The potentiating effect of caffeine on the γ-ray-induced chromosomal gaps was a little higher in S as compared with G2. These results lead to the conclusion that the alkylating agents and the γ-rays might induce 2 types of chromosomal gap.

G 2 repair and the formation of chromosomal aberrations—I. The effect of hydroxyurea and caffeine on maleic hydrazide-induced chromosome damage in Vicia faba

The potentiating effects of caffeine and hydroxyurea (HU), alone or in combination, on maleic hydrazide (MH)-induced chromosome damage were studied in root tips of Vicia faba. Rootswere exposed to 2.5 × 10 −3 M caffeine for 5 hr immediately or delayed until 5 hr after the MH treatment, and/or to 5 × 10 −3 M HU during the last 2 1 2 3 hr before fixation. The frequency of MH-induced chromatid aberrations was increased by both types of post-treatment, but whereas caffeine produced an increase of all types of aberrations without markedly influencing their relative proportions, HU affected the aberration yield not only quantitatively but also qualitatively. The largest potentiation by HU was obtained for gaps, chromatid breaks and isochromatid breaks of the non-union type, whereas chromatid exchanges and isochromatid breaks with sister union were comparatively little affected. Although a particularly dramatic enhancement was obtained when the MH-treated roots were first exposed to caffeine and then to HU, the frequency of aberrations obtained after a combined MH and caffeine treatment was not increased more by HU than that obtained after MH alone. Possible molecular mechanisms involved in the action of caffeine and HU on the formation of MH-induced chromatid aberrations are discussed.

The effect of caffeine posttreatment on X-ray-induced chromosomal aberrations in human blood lymphocytes in vitro.

The potentiating effect of caffeine on X-ray-induced chromosomal aberrations in human blood lymphocytes has been investigated, with special reference to cell cycle stages (G0 and G2). Both quantitative and qualitative differences in the yield of chromosomal aberrations were detected in caffeine-posttreated cells, depending on the cell stage irradiated. The studies on caffeine potentiating effects on X-irradiated G0 lymphocytes from normal adults, newborns, Down syndrome patients, and an ataxia telangiectasia patient pointed to interindividual variations in the response to caffeine potentiation among normal probands and a very profound effect in ataxia cells.

Investigations on the frequency of chromosome aberrations in bone marrow cells of chinese hamsters after simultaneous application of caffeine and cyclophosphamide.

The potentiating effect of caffeine (1,3,7-trimethylxanthine) on chemically induced chromosome aberrations was studied in bone marrow cells of chinese hamsters, exposed to the alkylating agent cyclophosphamide. Four experimental series were performed: In the first two tests caffeine (200 mg/kg) or cyclophosphamide (40 mg/kg), respectively, were administered. A third and fourth test was performed with caffeine plus cyclophosphamide (200 + 40 mg/kg and 35 + 40 mg/kg, respectively) simultaneously. Aberrations induced by cyclophosphamide (40 mg/kg) were strongly potentiated by simultaneous application of caffeine (200 mg/kg) not only additively but even synergistically. This increase of aberrations cannot be found after injection of the lower dose of caffeine (35 mg/kg).

The potentiating effect of caffeine on the production of chromosomal aberrations by alkylating agents in Chinese hamster cells and Vicia faba root-tips

The potentiating effect of caffeine on the production of chromosomal aberrations by alkylating agents in Chinese hamster cells and Vicia faba root-tips

The potentiating effect of caffeine on the production of chromosomal aberrations by alkylating agents in Chinese hamster cells and Vicia faba root-tips

The potentiating effect of caffeine on the production of chromosomal aberrations by alkylating agents in Chinese hamster cells and Vicia faba root-tips

Effect of caffeine on the neuromuscular junction of the frog, and its relation to external calcium concentration.

The effect of caffeine on the neuromuscular transmission was investigated by recording the end-plate potential (e. p. p.) of the frog sartorius muscle using an intracellular microelectrode.2. Caffeine increased the e. p. p. amplitude. The threshold concentration was about 0.5-1×10-4g/ml. The amplitude of e. p. p. was 158±16 of control size in the presence of 3×10-4g/ml caffeine.3. The quantum content was increased in the presence of 2×10-4g/ml and 2.5×10-4g/ml caffeine by factors of about 1.5 and 2, respectively.4. The frequency of the miniature end-plate potential (m. e. p. p.) was in creased by about 3-fold with 3×10-4g/ ml caffeine without an appreciable increase of m. e. p. p. size.5. The potentiating effect of caffeine became more marked when calcium concentration of the external medium was lowered, but the effect was usually transient when the calcium concentration was below 1/10 of the normal value.6. After a train of stimuli at 50 Hz for 30 sec post-tetanic potentiation occurred in the presence of caffeine with the same time course as in the control Ringer's solution.7. It is suggested that caffeine acts on the presynaptic nerve terminal and facilitates the release of calcium from the stored site within the nerve terminal.