铃蟾肽介导的豚鼠肠系膜下神经节非胆碱能迟慢兴奋性突触后电位
孔德虎*, 王刚, 王宏梅, 柯道平, 胡金兰, 祝延, 黄振信
安徽医科大学生理学教研室神经生理实验室, 合肥 230032
摘要: 应用细胞内记录技术, 对铃蟾肽(bombesin, BOM)在豚鼠离体肠系膜下神经节(inferior mesenteric ganglion, IMG)非胆碱能兴奋性突触传递中的作用进行了研究。重复电刺激突触前结肠神经, 有74.3% (52/70) IMG细胞可诱发迟慢兴奋性突触后电位(ls-EPSP)。在可引出ls-EPSP 的细胞中, 22% (4/18)细胞同时对BOM和SP敏感。用BOM持续灌流IMG, 可明显抑制对BOM敏感细胞的ls-EPSP, 对BOM不敏感细胞的ls-EPSP则无影响, 且BOM受体与SP受体间无交叉脱敏。BOM受体阻断剂tyr4［D-phe12］bombesin能明显可逆性地抑制BOM敏感细胞的ls-EPSP和去极化, 但对BOM不敏感细胞则无影响。研究结果提示, BOM可能是介导豚鼠IMG 细胞ls-EPSP的一种递质。
关键词: 铃蟾肽; P物质; 迟慢兴奋性突触后电位; 肠系膜下神经节; 豚鼠
中图分类号: Q421
Bombesin-mediated
non-cholinergic late slow excitatory postsynaptic potentials in guinea pig inferior mesenteric
ganglion in vitro
KONG De-Hu*, WANG Gang, WANG Hong-Mei, KE Dao-Ping, HU Jin-Lan, ZHU Yan, HUANG Zhen-Xin
Laboratory
of Neurophysiology, Department of Physiology,
Abstract: The effect of bombesin (BOM) on non-cholinergic excitatory synaptic transmission of the guinea pig inferior mesenteric ganglion (IMG) was investigated by intracellular recording. Repetitive stimulation of the colon nerves (1 ms, 25 Hz, 4 s) elicited a burst of action potentials, which was followed by a long-lasting depolarization in 74.3% (52/70) of the IMG neurons. The depolarization was not blocked by nicotinic (d-tubocurarine, 100 μmol/L) and muscarinic (atropine, 1 μmol/L) antagonists, but was eliminated in a low Ca2+/high Mg2+ Krebs solution, indicating that the depolarization was due to the release of non-cholinergic transmitters. Superfusing the ganglia with BOM (10 μmol/L, 1 min) induced a slow depolarization in 66.5% (109/164) neurons tested. The BOM response was not appreciably changed in low Ca2+/high Mg2+ Krebs solution (n=6, P>0.05), suggesting that BOM depolarized the neurons by acting directly on the postsynaptic membrane rather than via a release of other endogenous depolarizing substances. In a total of 102 cells that exhibited late slow excitatory postsynaptic potential (ls-EPSP), superfusion of the ganglia with BOM produced a membrane depolarization in 82 neurons (80%), while the remaining 20 cells (20%) exhibited no response to BOM. In 18 neurons with ls-EPSP, four (22%) neurons were sensitive to both BOM and SP; six (33%) and five (28%) neurons were only sensitive to BOM and SP, respectively. The remaining 3 (17%) neurons were insensitive to both BOM and SP. Membrane resistance (Rm) had no apparent change in 47.3%, 59.5 % of the neurons tested during the ls-EPSP (n=55) and BOM depolarization (n=84), respectively, but had a marked decrease in 38.2%, 27.4%, and a marked increase in the remaining 14.5%, 13.1% of the neurons. However, when the Rm change accompanying ls-EPSP was compared with that accompanying BOM depolarization (n=20) in the same neuron, the changes in Rm were always parallel. Moreover, ls-EPSP (n=6) and BOM depolarization (n=8) were all augmented by conditioning hyperpolarization. The extrapolated values of the reversal potentials of ls-EPSP and BOM depolarization were －46.0±8.0 and －50.0±7.0 mV (n=8, P>0.05), respectively. In 14 BOM-sensitive neurons, a ls-EPSP was elicited by repetitive colon nerve stimulation. Superfusion of BOM (10 μmol/L) in these cells initially caused a large depolarization and then membrane potential gradually subsided to resting level in the continuous presence of BOM. Stimulation of the presynaptic nerves at this time failed to elicit a detecable ls-EPSP in 2 neurons and induced a much smaller one in 10 cells, while the ls-EPSP in the remaining 2 neurons was not appreciably affected. On the other hand, prolonged superfusion of BOM had no effect on the amplitude and duration of ls-EPSP in 6 BOM-insensititive neurons studied (P>0.05). The amplitude and duration of SP-induced depolarization were not altered by prolonged superfusion of BOM (n=4, P>0.05). Superfusion of tyr4［D-phe12］bombesin (1 μmol/L, 10－15 min), a BOM receptor antagonist, did not cause any noticeable changes in passive membrane properties nor block nicotinic f-EPSPs, but markedly supressed (n=5) or completely abolished (n=11) BOM depolarization in all 16 neurons tested. Similarly, tyr4［D-phe12］bombesin partially or completely antagonized the ls-EPSP in 9 out of a total of BOM sensitive neurons (n=11). The ls-EPSP elicited in the remaining two neurons was insignificantly affected by this drug. However, following 10－20 min of wash with Krebs solution the ls-EPSP was reversed. In contrast, superfusion of the ganglia with tyr4［D-phe12］bombesin did not change the amplitude and duration (P>0.05) of ls-EPSP in 10 BOM-insensitive cells. Similarly, the amplitude and duration of SP-induced depolarization were not appreciably affected by tyr4［D-phe12］bombesin (n=6, P>0.05). In conclusion, our results indicate that BOM may be another transmitter mediating the ls-EPSP in the guinea pig IMG and that there is no cross-desensitization of BOM receptors and SP receptors.
Key words: bombesin; substance P; late slow excitatory postsynaptic potential; inferior mesenteric
ganglion; guinea pig