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Presence of functionally active protease‐activated receptors 1 and 2 in myenteric glia

Protease‐activated receptors (PARs) belong to the family of membrane receptors coupled to G‐proteins; their presence is reported in a wide variety of cells. The object of this study was to demonstrate the presence of PAR‐1 and PAR‐2 in myenteric glia of the guinea pig, and to elucidate the cellular mechanisms that are triggered upon receptor activation. Thrombin and PAR‐1 agonist peptide (PARP‐1) activate PAR‐1 with a maximum mean ± SEM change in intracellular calcium concentration with respect to basal level (Δ[Ca2+]i) of 183 ± 18 nm and 169 ± 6 nm, respectively. Trypsin and PAR‐2 agonist peptide (PARP‐2) activate PAR‐2 with a maximum Δ[Ca2+]i of 364 ± 28 nm and 239 ± 19 nm, respectively. Inhibition of phospholipase C by U73312 (1 µm) decreased the Δ[Ca2+]i due to PAR‐1 activation from 167 ± 10 nm to 87 ± 6 nm. The PAR‐2‐mediated Δ[Ca2+]i decreased from 193 ± 10 nm to 124 ± 8 nm when phospholipase C activity was inhibited. Blockade of sphingosine kinase with dimethylsphingosine (1 µm) decreased the Δ[Ca2+]i due to PAR‐2 activation from 149 ± 19 nm to 67 ± 1 nm, but did not influence the PAR‐1‐mediated Δ[Ca2+]i. PAR‐1 and PAR‐2 were localized in myenteric glia by immunolabeling. Our results indicate that PAR‐1 and PAR‐2 are present in myenteric glia of the guinea pig, and their activation leads to increases in intracellular calcium via different signal transduction mechanisms that involve activation of phospholipase C and sphingosine kinase.