Abstract: 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.

Key words: dopamine, ion transport, β-adrenoceptor, segment heterogeneity, lower distal colon