Serine proteases excite myenteric neurons through protease-activated receptors in guinea pig small intestine.
OBJECTIVE
Serine proteases are postulated to influence gastrointestinal function by stimulating protease-activated receptors (PARs). This study identified the effects on myenteric neurons of activating PARs and investigated underlying mechanisms of action.


METHODS
Intracellular electrophysiologic methods were used to study the effects of proteases on electrical and synaptic behavior of morphologically identified neurons in the guinea pig enteric nervous system. Fluorescent immunohistochemistry was used to study the chemical coding of neurons that responded to PARs stimulation.


RESULTS
Application of thrombin, trypsin, or mast cell tryptase evoked slowly activating excitatory responses reminiscent of slow synaptic excitation in enteric neurons. Synthetic activating peptides for PAR-1, -2, and -4 receptors mimicked the actions of the proteases. The depolarizing responses evoked by PARs were insensitive to cyclooxygenase inhibitors and were suppressed by agents that inhibit phospholipase C (PLC) or block intraneuronal receptors for inositol triphosphate. A majority of PAR-sensitive uniaxonal neurons expressed immunoreactivity for nitric oxide synthase. Most of the PAR-sensitive AH Dogiel morphologic type II neurons were immunoreactive for calbindin.


CONCLUSIONS
Excitatory responses to the serine proteases are mediated by PAR-1, -2, and -4 receptors. The mechanism of signal transduction involves stimulation of PLC and intraneuronal calcium mobilization and is independent of prostanoid formation.
Gao
Chuanyun
C
Department of Physiology and Cell Biology, The Ohio State University, College of Medicine and Public Health, Columbus, Ohio, USA.
Liu
Sumei
S
Hu
Hong-Zhen
HZ
Gao
Na
N
Kim
Gordon Y
GY
Xia
Yun
Y
Wood
Jackie D
JD
D000818:Animals; D004594:Electrophysiology; D006168:Guinea Pigs; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000378:metabolism*; D008297:Male; D009197:Myenteric Plexus / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin / Q000819:agonists / Q000502:physiology*; D012697:Serine Endopeptidases / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013618:Tachyphylaxis / Q000502:physiology
D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; D012697:Serine Endopeptidases; C112908:protease-activated receptor 4