The Effects Of TASK-1 Channel On The Regulation Of Central Respiratory Activity

Respiratory movement, known as a kind of rhythmic activity, can be regulated by respiratory center. The central respiratory chemoreceptors (CRCs) that is widely distributed in medulla oblongata can adjust the excitability of the neurons located in respiratory center of brain stem by sensing the changes of pH and the concentration of CO2 in brain, therefore , it plays an important role in keeping acid-base balance rapidly and maintaining homeostasis in vivo. CO2 known as the widely spread chemical substance may be one of the most effective stimulus taking part in respiratory regulation. In brain, the CO2 hydrates to be carbonate, and carbonate releases H+ by ionizing in the solution. The more CO2 intakes, the more H+ releases, which in turn has a remarkable effect on respiratory system. The increase of H+ in the brain sensed by CRCs, subsequently raising the excitability of the respiratory-related neurons and enhancing the output of respiration, hence regulates the behavior of breathing and keeps homeostasis. Recently, A newly potassium channel family with two-pore has been identified. Among them, TASK-1(TWIK-related acid-sensitive K+ channel-1; TWIK, for tandem P domains in a weak inwardly rectifying K+), called the'background'potassium channel, is such an open rectifier that is sensitive to extracellular pH in vivo. When the extracellular pH rises, the channel would be activated, increasing the potassium efflux and the excitability in respiratory-related neurons, or decreasing the excitability when the condition is absolutely opposite. Thus, the membrane of the neurons in the respiratory center and (or) CRCs may own TASK-1, which can sense the change of H+ or CO2 of the extracellular fluid and enhance the output of the respiration by increasing the excitability of the neurons. Therefore, we focus on the expression of TASK-1 mRNA in the brainstem respiratory-related neurons and the possible regulatory mechanisms of TASK-1 to the central chemorespiration, It can definitely help us better understand the possible function of TASK-1 channel in the respiratory center.Part 1. The Expression of TASK-1 channel mRNA in rat brainstem before and after the application of high-concentration CO2 Object:Our study was to investigate the expression of TASK-1 mRNA in the respiratory-related nucleus of rat brainstem and the effect of high-concentration CO2, providing strong evidence for morphology and indicating its possible roles in central respiratory regulation under physiological or pathological conditions.Methods: In situ hybridization staining was used to study the expression of TASK-1 channel mRNA in respirotary-related neurons of the rat brainstem before and after the inhalation high-concentration CO2(8%CO2+21%O2+71% N2). We detect the numbers and gray scale value of the neurons, which are positive expression of TASK-1 mRNA in different CO2 inhalation. According the prior detection, analyses were obtained for the effect of different CO2 inhalation onto the expression of TASK-1 mRNA in facial nucleus.Results: The results suggested that TASK-1 mRNAs were expressed in many nucleus of the rat brainstem, including gigantocellular reticular nucleus, facial nucleus, ambiguous nucleus and pre-B?tzinger complex in the ventrolateral medulla.There were three groups by in situ hybridized staining, of which the 30 min (high-concentration CO2 inhalation) group, the 60 min group were experimental group while the other is the control group (inhalation of air). Compared with the control group, TASK-1 mRNA-positive neurons remarkably increased(P<0.01) and gray scale value predominantly decreased ( P<0.05) both in the two experimental groups. However, there were no significant differences either in the quantity or the gray scale value of TASK-1 mRNA-positive neurons between each two experimental groups( P>0.05).Conclusion: Due to the fact that TASK-1 mRNA was widely located in the brainstem respiratory-related neurons, the assumption could be made that TASK-1 channel might participate in the regulation of central respiration by some unknown mechanisms. In our study, the level of TASK-1 mRNA in the positive-expression neurons was remarkably up-regulated after inhalation of 8%CO2, it seemed that TASK-1 channel might be the most attractive candidates sensing H+/CO2, and which participates the chemical regulation of central respiration. In addition, this channel also can change its expression in respiratory-related neurons of the brainstem by sensing the pH changes of cerebrospinal fluid, and then regulates the genesis of breathing in different condition.Part 2. The Effects of TASK-1 channel onto the respiratory movement in ratsObject:In order to investigate weather TASK-1 channel participates in the chemical regulation of central respiration, we monitored the electromyogram (EMG) of diaphragm by blocking TASK-1 channel to evaluate the changes of respiration in vivo.Methods: We evaluate the respiration by monitoring the electromyogram (EMG) of diaphragm during which injecting the blocker of TASK-1 (anandamide) into the lateral cerebral ventricle. Analysis of variance was used to compare the changes of inspiratory duration(TI), expiratory duration(TE), respiratory frequency (RF) and inspiratory amplitude (Amp) between pre-injection and post-injection AEA.Results: We observed all respiratory index from pre-injection to 35 min of post-injection, there were no significant differences between pre-injection and post-injection in normal sodium injection group as well as ethyl alcohol injection group (P>0.05). And the prior two groups were used to rule out the mechanical stimulation , the pressure of injection, and the stimulation of alcohol.In the blocker injection group,compared with pre-injection in the same group,a significant excitement of respiration occurred ten minutes after injection,which was characterized with a remarkable decrease in the TI and TE (P<0.01), and an increase in RF (P<0.01), except the Amp, which increased after injecting 5 min but still without any notable difference (P>0.05). These predominant differences of respiratory index also happened in the same time in both the ethyl alcohol injection group and the blocker injection group. Conclusion: The result indicates that injecting the blocker of TASK-1 (anandamide) in the lateral cerebral ventricle can block TASK-1 channel of CNS, such as facial nucleus, ambiguous nucleus and pre-B?tzinger complex, the effects can decrease potassium efflux in respiratory-related neurons, hence increase excitability of these neurons, which ultimately convey respiratory drive to the muscles of respiration.