Glucose and Glucose Transporters Regulate Lymphatic Pump Activity through Activation of the Mitochondrial ATP-Sensitive K⁺ Channel

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We investigated the pivotal roles of glucose and its transporter in the regulation of mechanical activity of isolated rat thoracic ducts and then examined whether or not mitochondrial ATP–sensitive K⁺ channels (mitoK_ATP) is involved in those responses. In the absence of extracellular glucose, the thoracic ducts showed pump activity during 120 min. Extracellular glucose caused a dose-dependent increase in the frequency of pump activity and a constriction in the thoracic ducts. Pump activity of the thoracic ducts in 0 mM glucose was completely inhibited in the presence of chlorogenic acid (an inhibitor of glucose-6-phosphatase). Cytochalasin B, an inhibitor of facilitative glucose transporter (GLUT), or phlorizin, an inhibitor of sodium-dependent glucose cotransporter (SGLT), significantly reduced the frequency of pump activity and dilated the thoracic ducts. 5-hydroxydecanoate (5-HD, a selective blocker of mitoK_ATP)–induced decrease in the frequency of pump activity was completely reversed by ruthenium red (an inhibitor of Ca²⁺ uniporter in mitochondria). Diazoxide (a selective opener of mitoK_ATP) significantly increased the frequency of pump activity. Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP, a protonophore of mitochondrial proton pump action) significantly reduced the frequency of pump activity and dilated the thoracic ducts. Collectively, these findings suggest that glucose derived from intracellular glycogen and/or through GLUT/SGLT in lymphatic smooth muscles contributes to the regulation of pump activity of isolated rat thoracic ducts, and that mitoK_ATP in the cells may partially serve as a modulator of the mechanical functions associated with mitochondrial Ca²⁺ uptake.