Smooth Muscles Contraction in Gastrointestinal Tract and New Concept of Enteric Neurotransmission: Fibroblast-like Cells

위장관 평활근 수축기전과 신경전달의 새로운 개념: Fibroblast-like Cells

This review provides information regarding an enteric neurotransmission from enteric nerve terminals to smooth muscles. In the gastrointestinal tract, phasic contractions are caused by electrical activity termed slow waves. Slow waves are generated and actively propagated by interstitial cells of Cajal (ICC). The initiation of pacemaker activity in the ICC is caused by release of $Ca^{2+}$ from inositol 1, 4, 5-trisphosphate ($IP_{3}$) receptor-operated stores, and the development of unitary currents. Summation of unitary currents causes depolarization and activation of a dihydropyridine-resistant $Ca^{2+}$ conductance that entrains pacemaker activity in a network of ICC, resulting in the active propagation of slow waves. Slow wave frequency is regulated by a variety of physiological agonists and conditions, and shifts in pacemaker dominance can occur in response to both neural and non-neural inputs. Fibroblast-like cells (FLCs) are also closely associated with nerve varicosities and are labelled robustly with antibodies for platelet-derived growth factor receptor ${\alpha}$ (PDGFR${\alpha}$), and expression of this receptor may be a powerful new means of isolating and evaluating the function of FLCs and the possible contribution of these cells in disease. PDGFR${\alpha}^{+}$ cells share similar anatomical distributions, and FLCs in colonic smooth muscle functionally express small conductance $Ca^{2+}$-activated $K^{+}$ channel (SK3). These findings are important to understand purinergic post-junctional responses.