Effects of inhibition of calcium and potassium currents in guinea-pig cardiac contraction: comparison of beta-caryophyllene oxide, eugenol, and nifedipine

Effects of terpenoid phenol derivatives on calcium current in canine and human ventricular cardiomyocytes

Concentration-dependent (10-1000 microM) effects of terpenoid phenol derivatives were studied on L-type Ca(2+) current in isolated canine and human ventricular cardiomyocytes using the whole-cell configuration of patch clamp technique. Carvacrol, thymol and eugenol suppressed peak Ca(2+) current at +5 mV, having EC(50) values and Hill coefficients of 98+/-11, 158+/-7 and 187+/-15 microM and 1.42+/-0.05, 2.96+/-0.43 and 1.6+/-0.1, respectively, in canine myocytes. Zingerone displayed a weak effect (estimated EC(50): 2+/-0.37 mM, Hill coefficient: 0.73+/-0.07), while vanillin and guaiacol failed to substantially modify Ca(2+) current up to the concentration of 1 mM. In addition to tonic block, thymol and carvacrol, but not eugenol, evoked marked rate-dependent block at 2 Hz. Carvacrol and eugenol accelerated inactivation of Ca(2+) current and caused leftward shift in the voltage dependence of steady-state inactivation without altering activation kinetics. Carvacrol, but not eugenol, increased the time constant of recovery from inactivation. These effects of carvacrol and eugenol developed rapidly and were largely reversible. In myocytes isolated from undiseased human hearts, the effect of carvacrol was similar to that observed in canine cells. It is concluded that suppression of cardiac Ca(2+) currents by phenol derivatives is influenced by the substituent in the benzene ring, and the blocking effect of these drugs may involve interactions with the inactivation machinery of the channel.

Ability of eugenol to reduce tongue edema induced by Dieffenbachia picta Schott in mice

Dieffenbachia picta Schott (Araceae), known in Brazil as "comigo-ninguém-pode" is an ornamental plant with toxic properties. Its juice, when chewed, causes a painful edema of the oral mucous membranes, buccal ulcerations and tongue hypertrophy. This acute inflammation sometimes becomes severe enough to produce glottis obstruction, respiratory compromise and death. Eugenol (4-alil-2-metoxiphenol), the essential oil extracted from Caryophyllus aromaticus (Myrtaceae) is widely used in odontology. In this study, our objective was to standardize, in mice, a measurable methodology for the tongue edema induced by the topical application of the D. picta stem juice; evaluate the effects of eugenol in this model and compare the results with emergency treatment used in hospitals. Our results show that in spite of a small increase in edema a few minutes after administration, emergency treatment reduced by 70% the overall edema. When compared with the combination of the above drugs, eugenol, even at the smallest dose of 5 microg/kg, regardless of the chosen administration route, or the moment the treatment began, presents better results in the reduction and inhibition of the tongue edema induced by the D. picta juice.

Vasorelaxant effects of eugenol on rat thoracic aorta

Eugenol is a natural pungent substance and the main component of clove oil, with vasorelaxant action. To elucidate some of the possible mechanisms involved in this action isometric tension was measured in aortic rings from male Wistar rats precontracted with phenylephrine (PHE, 10(-7) M) or KCl (75 mM). Responses to increasing concentrations of eugenol (10(-6)-10(-2) M) were obtained in the presence and absence of endothelium. In the presence of eugenol, dose-response curves to PHE (10(-9) to 10(-4) M) and KCl (5-125 mM) were displaced downwards. Concentration-dependent relaxation was observed in rings precontracted with PHE (10(-7) M) and KCl (75 mM). The tension increment produced by increasing external calcium concentration (0.25-3 mM) was also reduced by eugenol (300 microM) treatment. The inhibitory effects of eugenol (300 microM) were compared to those induced by nifedipine (0.01 microM), a selective Ca(2+) channel blocker, producing similar relaxant effects. Two other protocols were performed. After precontraction with PHE (10(-7) M), increasing concentrations of eugenol (10(-6)-10(-2) M) were used before and after N(w)-nitro-L-arginine (L-NAME, 10(-4) M) and methylene blue (10(-5) M) treatment. Eugenol-induced relaxation was reduced by endothelial damage (rubbing), L-NAME and methylene blue treatments. Results suggested that eugenol produces smooth muscle relaxation resulting from the blockade of both voltage-sensitive and receptor-operated channels that are modulated by endothelial-generated nitric oxide.

The effect of the isomers of cyclo(Trp-Pro) on heart and ion-channel activity

Cyclo(L-Trp-L-Pro) has shown potential for use in the treatment of cardiovascular dysfunction. The aim of the study was to determine the effects of the isomers of cyclo(Trp-Pro) - cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro), cyclo(D-Trp-L-Pro) and cyclo(D-Trp-D-Pro) - on heart and ion-channel activity. The effects on L-type Ca(2+)-channel, Na(+)-channel and inward rectifier K(+)-channel activity were determined by using the whole-cell patch-clamp technique on myocytes of guinea-pig origin. Dependence on the membrane potential in terms of Ca(2+)-channel activity was also investigated. A modified Langendorff method was used to determine the effects of the isomers on heart rate, coronary flow, duration of ventricular tachycardia and arrhythmia, time to sinus rhythm and QRS interval on the rat isolated heart. Cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), 100 microM, showed agonism towards Ca(2+)-channel activity, while cyclo(D-Trp-L-Pro) caused a blockage of the current. The action of cyclo(D-Trp-L-Pro) was shown to be independent of membrane potential. No significant effect (P > 0.05) on the inward rectifier K(+) current was observed in the presence of cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), while antagonism was noted in the presence of cyclo(L-Trp-L-Pro) and cyclo(D-Trp-L-Pro). All isomers showed antagonist effects on the Na(+) channel. No adverse effects were noted on chronotropic effects in the presence of 200 microM cyclo(L-Trp-L-Pro) and cyclo(D-Trp-D-Pro) (P > 0.05), while cyclo(L-Trp-D-Pro) significantly increased the heart rate. Cyclo(D-Trp-L-Pro) significantly reduced the heart rate (P < 0.05). In addition, no significant effects were observed on the coronary flow rate in the presence of the isomers. All isomers significantly reduced the duration of ventricular tachycardia and arrhythmia, as well as the time to sinus rhythm. Furthermore, no change in the QRS intervals was noted in the presence of the isomers in comparison with the control, with a significant increase being noted for cyclo(D-Trp-D-Pro) (P < 0.05) in reference to the other isomers. The isomers thus show antiarrhythmic potential and may manifest as novel agents in the treatment of cardiovascular dysfunction, since a decrease in ventricular fibrillation may reduce the mortality rates in acute myocardial infarction.