多巴胺引起大鼠结肠黏膜离子转运的节段异质性

目的探究多巴胺(DA)引起的大鼠远端结肠黏膜离子转运在不同节段的异质性及其可能的原因。方法用短路电流技术(ISC)探测DA引起的大鼠远端结肠黏膜离子转运在不同节段的差异及其介导受体;用realtime-PCR方法检测介导DA反应的受体在大鼠结肠黏膜不同节段的表达是否具有差异性。结果DA在结肠近肛门端(结直肠交界处,DC1)引起的短路电流(ΔISC)为(-14.32±3.14)μA/cm2,明显高于远端结肠的其他部位(-3.19±1.44)μA/cm2(P<0.01)。多巴胺D1样、D2样受体拮抗剂及α受体拮抗剂phentolamine均不能抑制该反应。但β1和β2肾上腺素能受体拮抗剂atenolol和ICI118、551却明显抑制多巴胺产生的反应,抑制程度分别为63.79%(P<0.05),87.27%(P<0.01)。realtime-PCR结果显示,在远端结肠黏膜上,介导该反应的β1和β2受体的mRNA在远离肛门处的远端结肠(DC4)的表达为DC1表达量的48.6%(P<0.001)和56.5%(P<0.05)。结论DA在大鼠远端结肠引起的黏膜离子转运具有异质性,即在DC1的反应明显高于远端结肠的其他部位,这可能与为介导该反应的β1和β2肾上腺素能受体在DC1的高表达有关。

The Segmental Heterogeneity of Dopamine-induced Ion Transport in Rat Distal Colon

Objective The present study focuses on the segmental heterogeneity of dopamine(DA)-induced ion transport within rat distal colon,and the possible underlying mechanism.Methods Distal colonic mucosa was used to investigate the effect of DA in different segments of distal colon and the related receptors mediating the reaction by short circuit current(I_SC).Then the mRNA expression of the mediated receptors in the mucosa of different parts of distal colon analyzed by real time-PCR.Results DA-induced ΔI_SC in the segment near anus(lower distal colon,DC1) was(-14.32±3.14)μA/cm²,and was significantly larger than that at any other segments of distal colon(-3.19±1.44)μA/cm²(P<0.01).Dopaminergic D₁,D₂ receptor antagonist did not block the effect of DA,and nonselective α-adrenoceptor antagonist phentolamine could not suppress the effect also.But selective β₁adrenoceptor blocker atenolol and β₂-adrenoceptor blocker ICI 118,551 inhibited significantly the effects by 63.79%(P<0.05) and 87.27%(P<0.01) respectively,which suggested that DA-induced ΔI_SC was mediated by β₁-and β₂-adrenoceptor,but not dopaminergic receptors.The results of real time-PCR showed that the mRNA expression of β₁-and β₂-adrenoceptor in the mucosa of DC4 was 48.6%(P<0.001),and that in DC1 56.5%(P<0.05) respectively.Conclusion DA-induced ΔI_SC is predominant at DC1,and this may be due to higher expression of the mediated receptors(β₁-and β₂-adrenoceptors) in DC1 than those in DC4.The results suggest that the dopamine may play an important role in the regulation of ion transport in lower distal colon(colorectum),where the predominant expressions of adrenoceptors might be related to the formative process of some stress-related colorectal diseases.