Abstract
Cyclooxygenase enzymes (COX) generate intermediates in the prostaglandin (PG) cascade. COX-1 is constitutively expressed in many cells, and COX-2 is typically thought to be an inducible isoform. We evaluated constitutive expression and function of COX-2 in murine gastric muscles. Immunohistochemistry showed COX-2-like immunoreactivity (COX-2-LI) in myenteric neurons. Half the neurons with COX-2-LI expressed nitric oxide synthase (NOS). COX-2-LI was not observed in smooth muscle cells. Interstitial cells of Cajal within muscle layers (IC-IM) expressed COX-2-LI, suggesting a novel role for IC-IM. Molecular studies verified expression of COX-2 in gastric muscles. Quantitative polymerase chain reaction (PCR) showed equal expression of COX-1 and COX-2 in the antrum. COX-2 was more abundant in fundus. Indomethacin and GR253035X, a COX-2 inhibitor, increased antral phasic contractions and potentiated responses to ACh. Indomethacin, but not GR253035X, increased contractions and potentiated responses in tissues of COX-2 knockout mice. Indomethacin and GR253035X reduced tone in the fundus. COX-2 is constitutively expressed by IC-IM and neurons in the stomach and at levels similar to COX-1. Prostanoids produced by COX-2 regulate mechanical activities of fundus and antral muscles.
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