OBJECTIVETo investigate the effect of interstitial cells of Cajal (ICC) on contraction of intestinal tract smooth muscle induced by motilin receptor agonist.

METHODSTwo kinds of smooth muscle segments were isolated from the duodenum and colon of rabbit. Both kinds of smooth muscle were divided into two groups: group a (normal ICC group of duodenum); group c (impaired ICC group of duodenum); group b (normal ICC group of colon); group d (impaired ICC group of colon), each group contained 20 segments. The impairment of ICC was induced by selectively destroying ICC in the smooth muscle via treatment with methylene blue plus light. Then the frequency and amplitude of contraction of group a and c, group b and d was compared. Then motilin receptor agonist (ABT-229) was added into the Krebs solution, the frequency and amplitude of smooth muscle contraction before and after adding ABT-229 were recorded and compared.

RESULTSThe electron microscopy demonstrated that ICC in methylene blue plus light group were destroyed; the smooth muscle cells and neuron scattered close to ICC were normal. In group a, the contraction frequency, (17.89 +/- 1.88) times/min, was significantly lower as compared with that measured after ABT-229 was added [(18.76 +/- 1.18) times/min (P > 0.05)]; the amplitude of group a was (343 +/- 28) mg, which was lower as compared with that after adding ABT-229 [(597 +/- 68) mg (P < 0.001)]; in group b, the frequency was (5.89 +/- 1.03) times/min, the amplitude was (724 +/- 85) mg, after ABT-229 was added, the construction frequency increased to (8.45 +/- 0.69) times/min (P < 0.001), and the amplitude was (897 +/- 89) mg (P < 0.05), which was not affected by pretreatment with TTX, however it could be weakened by nifedipine significantly. In group c and d, the rhythmic contraction almost disappeared: in group c the contraction frequency was (1.06 +/- 0.24) times/min, and the amplitude were (50 +/- 10) mg. In group d, the amplitude and frequency significantly decreased as compared with the normal group (P < 0.001), in group c, and d, no significant difference in amplitude and frequency was found between the values measured before and after adding ABT-229 (P > 0.05). After Ach (100 micromol/L) was added, both group c and d could generate contraction.

CONCLUSIONICC may play an important role in the rhythmic contraction of intestinal tract. The promoting effect of motilin receptor agonist on intestinal tract may be mediated by ICC. ICC deficiency may cause functional impairment of gastrointestinal tract motivation. The medication may become ineffective when the number of ICC is reduced to a certain extent or the network of ICC is incomplete.