Abstract
Mucin release from hamster tracheal surface epithelial(HTSE) cells can be stimulated by extracellular ATP via activation of P$_2$ purinoceptors located on the cell surface which appears to be coupled to phospholipase C via G proteins. However, our preliminary data indicate that the ATP-induced mucin release involves, in part, activation of PKC, but not an increase in the intracellular Ca++ level, suggesting the presence of another pathway which is separate from the PLC-PKC pathway, In this study, we intended to confirm the previous observation and subsequently identify an additional mechanism. Confluent HTSE cells were metabolically labeled with either $^3$H-glucosamine or $^3$H-arachidonic acid(AA), and release of either $^3$H-mucin or $^3$H-AA was quantified following various treatments. $^3$H-mucin was assayed using the sepharose CL-4B gel-filtration method, whereas $^3$H-AA liberation was measured by counting $^3$H-radioactivity in the chase medium. We found that: (1)Desensitization of PKC by pretreatment with PMA completely abolished the mucin releasing effect of PMA but partially inhibited the ATP-induced mucin release; (2) ATP increases release of $^3$H-AA in a dose-dependent fashion; (3) mepacrine, an inhibitor of PLA$_2$, attenuates ATP-induced mucin release in a dose-dependent fashion. These results confirm our previous notion that the PLC-PKC pathway is responsible, in part, for ATP-induced mucin release. Furthermore, activation of PLA$_2$ appears to be an additional pathway which is involved in ATP-induced mucin release.