Signaling pathways mediating gastrointestinal smooth muscle contraction and MLC20 phosphorylation by motilin receptors

被引:59
作者
Huang, J
Zhou, HP
Mahavadi, S
Sriwai, W
Lyall, V
Murthy, KS
机构
[1] Virginia Commonwealth Univ, Dept Physiol, Richmond, VA 23298 USA
[2] Virginia Commonwealth Univ, Dept Med, Richmond, VA 23298 USA
来源
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY | 2005年 / 288卷 / 01期
关键词
interdigestive gut hormone; Rho kinase; G protein signaling;
D O I
10.1152/ajpgi.00305.2004
中图分类号
R57 [消化系及腹部疾病];
学科分类号
摘要
The signaling cascades initiated by motilin receptors in gastric and intestinal smooth muscle cells were characterized. Motilin bound with high affinity (IC50 0.7 +/- 0.2 nM) to receptors on smooth muscle cells; the receptors were rapidly internalized via G protein-coupled receptor kinase 2 (GRK2). Motilin selectively activated G(q) and G(13), stimulated Galpha(q)-dependent phosphoinositide (PI) hydrolysis and 1,4,5-trisphosphate (IP3)-dependent Ca2+ release, and increased cytosolic free Ca2+. PI hydrolysis was blocked by expression of Galpha(q) minigene and augmented by overexpression of dominant negative RGS4(N88S) or GRK2(K220R). Motilin induced a biphasic, concentration-dependent contraction (EC50 = 1.0 +/- 0.2 nM), consisting of an initial peak followed by a sustained contraction. The initial Ca2+-dependent contraction and myosin light-chain ( MLC)(20) phosphorylation were inhibited by the PLC inhibitor U-73122 and the MLC kinase inhibitor ML-9 but were not affected by the Rho kinase inhibitor Y27632 or the PKC inhibitor bisindolylmaleimide. Sustained contraction and MLC20 phosphorylation were RhoA dependent and mediated by two downstream messengers: PKC and Rho kinase. The latter was partly inhibited by expression of Galpha(q) or Galpha(13) minigene and abolished by coexpression of both minigenes. Sustained contraction and MLC20 phosphorylation were partly inhibited by Y27632 and bisindolylmaleimide and abolished by a combination of both inhibitors. The inhibition reflected phosphorylation of two MLC phosphatase inhibitors: CPI-17 via PKC and MYPT1 via Rho kinase. We conclude that motilin initiates a Galpha(q)-mediated cascade involving Ca2+/calmodulin activation of MLC kinase and transient MLC20 phosphorylation and contraction as well as a sustained Galpha(q)- and Galpha(13)-mediated, RhoA-dependent cascade involving phosphorylation and contraction.
引用
收藏
页码:G23 / G31
页数:9
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