Changes in the Muscarinic Receptors on the Colonic Smooth Muscles of Rats with Spinal Cord Injury

Abstract

ObjectiveTo investigate changes in (1) the colonic response to acetylcholine (Ach), (2) the muscarinic (M) receptors in the colon, and (3) the levels of colonic contraction-related proteins after a spinal cord injury (SCI).MethodWe divided 16 Sprague-Dawley rats into 2 groups: the control group and the SCI group. A spinal cord transection was performed surgically at the T10 vertebral level. After 1 week, the entire colon was divided into 2 segments, the proximal and distal colon. Each segment was mounted in a longitudinal or circular muscle direction in a 10-ml organ bath. We determined the intergroup differences as percentage changes in contractility after Ach treatment alone, Ach treatment with M2 receptor antagonist (AQ-RA741) pretreatment, and Ach treatment with M3 receptor antagonist (4-DAMP) pretreatment. Western blot analyses were performed to determine the expression level of RhoA, and heat shock protein 27 (HSP27).ResultsCompared to the control rats, the SCI rats showed an increased response to Ach along both the directions in the proximal colon (p<0.05). Compared to the control group, in the SCI group, the Ach response was significantly different in the proximal segment under AQ-RA741 pretreatment (p<0.05) and in the distal segment under 4-DAMP pretreatment (p<0.05). Findings of the western blot analyses showed a significant decrease in the level of protein gene product 9.5 in the proximal and distal colon and a significant increase in the level of RhoA and HSP27 in the proximal colon of the SCI rats.ConclusionOur results suggest that changes in colonic contractility after SCI are partly attributable to changes in the M receptor subtypes.