Inhibitory Effects Of Lidocaine On Isolated Trachea In Rat

ObjectiveLidocaine is one of the most widely used local anesthetics. Lidocaine is used intravenously as an anti - arrhythmic agent. Recently, many studies have shown that Lidocaine had a relaxant effect on arterial preparations and other smooth muscle preparations. There are a lot of investigations into the effect of Lidocaine on vascular smooth muscle. Its mechanism includes the inhibition of potential - dependent channel ( PDC ) and decreased influx of extra - cellular Ca2+. However, the studies about the mechanism of Lidocaine on airway smooth muscle are very few, and the present studies are only on the isolated guinea pig tracheal preparations and its mechanism is not completely understood. This stud-y was taken to observe the effects of Lidocaine on contractions induced by ACh, KCl and CaCl2 on isolated rat tracheal strips, and the inhibitory action of Lidocaine on the two contractive components evoked by ACh to research the effect and mechanism of Lidocaine on tracheal smooth muscle.Methods1. Isolated trachea preparationWistar rats (9,6 350 - 480 g ). Rats were stunned and exsanguinated to death. The trachea was rapidly dissected out, fat and connective tissues were gently removed in cold Krebs solution aired with 95% O2 +5% CO2. The segments of trachea were cut into helical strips that were 3 mm width and 1.5 cm length, respectively. Each isolated tracheal strips were suspended in organ bathscontaining 10 ml Krebs solution.2. Experimental methodThe tension of the Rat isolated trachea was recorded by an isometric force transducer coupled with a carrier amplifier and recorded by ink - writing recorders. Organ baths were maintained at 37 ± 1℃ and gassed with 95% O2 and 5% CO2 to achieve a pH of 7.4 -7. 5. Tissues were washed for 3 times by repeatedly replacing Krebs solution and then allowed to equilibrate for a period of 90 min under 1. 5g resting tension, then observe and compare the effects of Lidocaine on contractions induced by ACh, KCl and CaCl2 on isolated rat tracheal strips and the inhibitory action of Lidocaine on the two contractive components evoked by ACh with that of verapamil.Results1. Effect of Lidocaine on the contraction of ACh and KCl and propranolol, L - NAME on the spasmolytic action of LidocaineACh and KCl both can increase the tension of rat tracheal preparation. Li-docaine (3.0 mmol/L) caused (97.2 ±5. 1) % and (64. 1 ±13.5) % relaxation of KCl and ACh treated isolated tracheal strips, respectively (n = 8 ). The relaxation responses to Lidocaine were not affected by the presence of either L -NAME or proranlolol.2. Effect of Lidocaine on concentration -response curves of ACh, KCl or CaCl2Lidocaine produced a concentration - dependent inhibition on contractions induced by ACh, KCl or CaCl2. The concentration - effect curves were moved to the right and the maximal contractions were depressed. The pD'2 values of Lidocaine on contractions induced by ACh, KCl or CaCl2 were 2.4 ±0.1, 3.6 ±0. 1 and 3. 8 ±0.1, respectively, while pD'2 of Verapamil were 4.3 ±0.1, 6.1 ± 0.2 and 7.5 ±0.1, respectively.3. Effect of Lidocaine on two phases contraction induced by AChIn Ca2+ - free Krebs solution, Lidocaine had a concentration - dependent inhibitory effect on ACh - induced Ca2+ release in tracheal smooth muscle andthe percentages of inhibition at dose of 0. 69 and 3. 45 mmol/Lwere (41. 7 ± 12.8)% (n = 15) and (98.9 ±1.4)% (n = 13), respectively. Lidocaine inhibited contraction depending on extra - cellular Ca2+ and the percentages of inhibition at dose of 0. 69 and 3.45 mmol/L were (6.1 ±6. 6)% (n = 15) and (60.9 ±7.8)% (n = 13), respectively. The feature of actions of Lidocaine was similar to that of 34. 5 μmol/L Verapamil.DiscussionThe experiments showed that Lidocaine obviously relaxed the contraction induced by ACh and KCl, especially has a greater relaxation on KCl induced contraction. High potassium cause tracheal smooth muscle membrane depolarization , which can open voltage operated calcium channels ( VOCC ) and the smooth muscle contraction when calcium influx. In the experiment, Lidocaine not only inhibited the KCl induced contraction in normal Krebs solution but also moved the calcium concentration - dependent contraction curves to the right in high K+ depolarization medium and depressed the maximum responses, so the inhibition was in a noncompetitive manner. These results suggest that Lidocaine may have Ca2 + antagonistic properties and can inhibit extracellular Ca2+ influx through VOCC.In Ca2+ - free Krebs solution, release of Ca2+ from the sarcoplasmic reticulum is responsible for the contraction of phase Ⅰ induced by ACh, whereas influx of extra - cellular Ca2 + is for the contraction of phase Ⅱ with administration of CaCl2. Lidocaine had a greater inhibition on contraction induced by phase Ⅰ than that on contraction induced by phase H , which indicated Lidocaine had a higher inhibition on Ca2+ release than on extra -cellular Ca 2+ influx. The pD'2 of KCl is greater than that of ACh. From all these we have known that the sensitivity order of Lidocaine for three Ca2+ -elevating pathways is; VOCC > intracellular Ca2+ release > ROCC.To investigate if Lidocaine has any effect on NO releaseing, the present experiments observe the effect of NO synthase inhibitor, L - NAME, on Lidocaine. The results showed that pre - incubated with L - NAME, which had little...