Effect Of GABA On Smooth Muscle Spontaneous Contraction Activities Of Mouse Ileum

Jessen's researches confirmed thatγ-aminobutytric acid(GABA) is not only been in the central nervous system, but also been in the peripheral nervous systems such as enteric nervous system. GABA may modulate the gastrointestinal motilities of rat,guinea- pig,dog and cat. Some researches suggest that effect of GABA on the gastrointestinal spontaneous contraction is very complex, depending on the position within the gastrointestinal tract and the animal species studied. The complex actions of GABA maybe relate to the different type receptors of GABA or the interactions between non-adrenergic non-cholinergic neurons and GABA. The exact reasons were not sure. Few reports, however, were founded about distribution of GABA in the alimentary tract and effects of GABA on spontaneous contraction of the smooth muscle in mice.In our experiments, using the immunohistochemical method, the distributions of GABA were explored in the mouse ileum. The contraction changes of the isolated smooth muscle strips were recorded by tension transducer, and the change of the tension was used as the marker to evaluate the effects of GABA. The effects of GABA on the contraction of mouse ileum and the influence of L-NNA, ODQ, propranolol on the action of GABA were analyzed. We also investigated the interactions between GABA and NO,β-receptor.Results:1. The presence of GABA ergic neurons in the myenteric plexus and submucosal neurons were demonstrated in the ileum of mouse.2. GABA inhibited the spontaneous contraction of mouse ileum at the concentrations ranging from 1×10-6 to 1×10-3mol/L(P<0.05,n=10). 1×10-6mol/L GABA decreased the contraction amplitudes by(34.7±7.4)%.3. After incubated the preparations with picrotoxin, GABAA receptor inhibitor, the inhibitory effects on the contraction of mouse ileum caused by GABA have no significant change. (P>0.05,n=7).4. When GABA (1×10-6mol/L) was added in the presence of L-NNA(1×10-5mol/L), inhibition of nitric oxide synthase (NOS), The amplitude inhibitory percent with(15.9±3.8)% was significantly different from amplitude inhibitory percent of single GABA (1×10-6mol/L).(p<0.05,n=6).5. ODQ(1×10-4mol/L) was used to incubate the preparations for 15 min before addition of GABA(1×10-6mol/L). The contraction amplitudes changed from (0.35±0.05)g to (0.34±0.05)g.They did not changed .The percent of the inhibition amplitudes reduced from (33.2±7.3)% to (4.8±1.3)% .They have statistical signification. That is to say, ODQ reduced the inhibitory effects of GABA.6. When the preparations were pre-incubated with L-Arg(5×10-7mol/L), the effect of GABA at the concentration of 1×10-6mol/L was fallen. But the effect of GABA at the concentration of 1×10-3mol/L had no significant change.7. Propranolol (3×10-5mol/L) inhibited the effect of GABA at the concentration of 1×10-6mol/L and 1×10-3mol/L. After the strips were pretreated with propranolol (3×10-6mol/L), the inhibitory percent of contractile amplitude of GABA (1×10-6mol/L) reduced from (34.4±7.2)% to (14.6±2.6) % compared with single GABA(1×10-6mol/L).Conclusion:GABA-ergic fibers distributed in mouse ileum. GABA inhibited the spontaneous contraction of mouse ileac smooth muscle, this inhibitory effect is influenced by NO and the excitation ofβ-receptor. But the effect is independent of the Cl- channel that gated by GABAA receptor.