Department of Cell Biology, Physiology and Immunology and Neuroscience Institute, Universitat Autònoma de Barcelona, Barcelona, Spain.
Acta Physiol (Oxf). 2014 Dec;212(4):293-305. doi: 10.1111/apha.12408.
ATP and nitric oxide (NO) are released from enteric inhibitory motor neurones and are responsible for colonic smooth muscle relaxation. However, how frequency of neural stimulation affects this cotransmission process and the post-junctional responses has not been systematically characterized in the human colon.
The dynamics of inhibitory cotransmission were studied using different protocols of electrical field stimulation (EFS) to characterize the inhibitory junction potentials (IJP) and the corresponding relaxation in colonic strips obtained from 36 patients.
Single pulses elicited a fast IJP (IJPf(MAX) = -27.6 ± 1.6 mV), sensitive to the P2Y1 antagonist MRS2500 1 μm, that ran down with frequency increase leaving a residual hyperpolarization at high frequencies (IJPf∞ = -3.7 ± 0.6 mV). Accordingly, low frequencies of EFS caused purinergic transient relaxations that cannot be maintained at high frequencies. Addition of the P2Y1 agonist MRS2365 10 μm during the purinergic rundown did not cause any hyperpolarization. Protein kinase C (PKC), a putative P2Y1 desensitizator, was able to reduce the amplitude of the IJPf when activated, but the rundown was not modified by PKC inhibitors. Frequencies higher than 0.60 ± 0.15 Hz were needed to evoke a sustained nitrergic hyperpolarization that progressively increased reaching IJPs∞ = -13 ± 0.4 mV at high frequencies and leading to a sustained inhibition of spontaneous motility.
Changes in frequency of stimulation possibly mimicking neuronal firing will post-junctionally determine purinergic vs. nitrergic responses underlying different functional roles. NO will be responsible for sustained relaxations needed in physiological processes such as storage, while purinergic neurotransmission evoking sharp transient relaxations will be dominant in processes such as propulsion.
三磷酸腺苷（ATP）和一氧化氮（NO）由肠抑制性运动神经元释放，负责结肠平滑肌松弛。然而，神经刺激的频率如何影响这种共传递过程和突触后反应，在人类结肠中尚未系统地描述。
使用不同的电场刺激（EFS）方案研究抑制性共传递的动力学，以表征从 36 名患者获得的结肠条带中的抑制性突触后电位（IJP）和相应的松弛。
单脉冲引发快速 IJP（IJPf(MAX)=-27.6±1.6 mV），对 P2Y1 拮抗剂 MRS2500（1μm）敏感，随着频率增加而衰减，在高频时留下残余超极化（IJPf∞=-3.7±0.6 mV）。因此，EFS 的低频引起短暂的嘌呤能松弛，无法在高频下维持。在嘌呤能衰减过程中添加 P2Y1 激动剂 MRS2365（10μm）不会引起任何超极化。蛋白激酶 C（PKC），一种潜在的 P2Y1 脱敏剂，在激活时能够减小 IJPf 的幅度，但 PKC 抑制剂不能改变衰减过程。需要高于 0.60±0.15 Hz 的频率才能引发持续的氮能超极化，该超极化逐渐增加，在高频时达到 IJPs∞=-13±0.4 mV，并导致自发性运动的持续抑制。
刺激频率的变化可能模拟神经元放电，将在突触后水平决定嘌呤能与氮能反应，从而发挥不同的功能作用。NO 将负责储存等生理过程所需的持续松弛，而嘌呤能神经传递引发的尖锐短暂松弛将在推进等过程中占主导地位。
