Glucose and glucose transporters regulate lymphatic pump activity through activation of the mitochondrial ATP-sensitive K+ channel

Abstract

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 mitochondrial ATP-sensitive K+ channels (mitoK ATP) are 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 facili-tative 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. A decrease in the frequency of pump activity induced by 5-hydroxydecanoate (5-HD, a selective blocker of mitoKATP) was completely reversed by ruthenium red (an inhibitor of Ca2+ uniporter in mitochondria). Diazoxide (a selective opener of mitoKATP) 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 the pump activity of isolated rat thoracic ducts, and that mitoKATP in the cells may partially serve as a modulator of the mechanical functions associated with mitochondrial Ca2+ uptake.