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Protease‐activated receptors modulate excitability of murine colonic smooth muscles by differential effects on interstitial cells
Author(s) -
Sung Tae Sik,
Kim Heung Up,
Kim Jeong Hwan,
Lu Hongli,
Sanders Kenton M.,
Koh Sang Don
Publication year - 2015
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2014.285148
Subject(s) - interstitial cell of cajal , receptor , myocyte , microbiology and biotechnology , interstitial cell , motility , chemistry , protease activated receptor , biology , endocrinology , biochemistry , platelet , smooth muscle , immunology , thrombin
Key points Activation of protease‐activated receptors (PAR) regulates gastrointestinal (GI) motility but little is known about the cells and mechanisms in GI muscles responsible for PAR responses. Using mouse cells, we found high levels of F2r and F2rl1 PAR‐encoding genes expressed in purified platelet‐derived growth factor α‐positive (PDGFRα + ) cells in comparison to other cells in colonic muscles. PAR1 and PAR2 agonists caused transient hyperpolarization and relaxation of colonic muscles, with relaxation responses followed by excitation. The inhibitory phase was inhibited by apamin and mediated by activation of small conductance calcium‐activated potassium channels in PDGFRα + cells. The excitatory response resulted largely from activation of a chloride conductance in interstitial cells of Cajal; small amplitude inward currents were generated in smooth muscle cells by PAR activation, but these responses were too small to be resolved in intact muscles. PAR receptor responses are integrated responses generated by cells of the smooth muscle, interstitial cells of Cajal and PDGFRα + cells (SIP syncytium).Abstract Protease‐activated receptors (PARs) are G protein‐coupled receptors activated by proteolytic cleavage at their amino termini by serine proteases. PAR activation contributes to the inflammatory response in the gastrointestinal (GI) tract and alters GI motility, but little is known about the specific cells within the tunica muscularis that express PARs and the mechanisms leading to contractile responses. Using real time PCR, we found PARs to be expressed in smooth muscle cells (SMCs), interstitial cells of Cajal (ICC) and platelet‐derived growth factor receptor α positive (PDGFRα + ) cells. The latter cell‐type showed dominant expression of F2r (encodes PAR1) and F2rl1 (encodes PAR2). Contractile and intracellular electrical activities were measured to characterize the integrated responses to PAR activation in whole muscles. Cells were isolated and ICC and PDGFRα + cells were identified by constitutive expression of fluorescent reporters. Thrombin (PAR1 agonist) and trypsin (PAR2 agonist) caused biphasic responses in colonic muscles: transient hyperpolarization and relaxation followed by repolarization and excitation. The inhibitory phase was blocked by apamin, revealing a distinct excitatory component. Patch clamp studies showed that the inhibitory response was mediated by activation of small conductance calcium‐activated K + channels in PDGFRα + cells, and the excitatory response was mediated by activation of a Cl − conductance in ICC. SMCs contributed little to PAR responses in colonic muscles. In summary, PARs regulate the excitability of colonic muscles; different conductances are activated in each cell type of the SMC–ICC–PDGFRα + cell (SIP) syncytium. Motor responses to PAR agonists are integrated responses of the SIP syncytium.