Role of BK(Ca) in Stretch-Induced Relaxation of Colonic Smooth Muscle

Stretch-induced relaxation has not been clearly identified in gastrointestinal tract. The present study is to explore the role of large conductance calcium-activated potassium channels (BK(Ca)) in stretch-induced relaxation of colon. The expression and currents of BK(Ca) were detected and the basal muscle tone and contraction amplitude of colonic smooth muscle strips were measured. The expression of BK(Ca) in colon is higher than other GI segments (P < 0.05). The density of BK(Ca) currents was very high in colonic smooth muscle cells (SMCs). BK(Ca) in rat colonic SMCs were sensitive to stretch. The relaxation response of colonic SM strips to stretch was attenuated by charybdotoxin (ChTX), a nonspecific BK(Ca) blocker (P < 0.05). After blocking enteric nervous activities by tetrodotoxin (TTX), the stretch-induced relaxation did not change (P > 0.05). Still, ChTX and iberiotoxin (IbTX, a specific BK(Ca) blocker) attenuated the relaxation of the colonic muscle strips enduring stretch (P < 0.05). These results suggest stretch-activation of BK(Ca) in SMCs was involved in the stretch-induced relaxation of colon. Our study highlights the role of mechanosensitive ion channels in SMCs in colon motility regulation and their physiological and pathophysiological significance is worth further study.