ABSTRACT
ATP-sensitive K+ (KATP) channels in pancreatic ß cells are comprised of pore-forming subunits (Kir6.2) and modulatory sulfonylurea receptor subunits (SUR1). The ATP sensitivity of these channels enables them to couple metabolic state to insulin secretion in ß cells. Antidiabetic sulfonylureas such as glibenclamide target SUR1 and indirectly suppress Kir6.2 activity. Glibenclamide acts as both a primary and a secondary secretagogue to trigger insulin secretion and potentiate glucose-stimulated insulin secretion, respectively. We tested whether blocking Kir6.2 itself causes the same effects as glibenclamide, and found that the Kir6.2 pore-blocking venom toxin SpTx1 acts as a strong secondary, but not a strong primary, secretagogue. SpTx1 triggered a transient rise of plasma insulin and lowered the elevated blood glucose of diabetic mice overexpressing Kir6.2 but did not affect those of nondiabetic mice. This proof-of-concept study suggests that blocking Kir6.2 may serve as an effective treatment for diabetes and other diseases stemming from KATP hyperactivity that cannot be adequately suppressed with sulfonylureas.
Subject(s)
Diabetes Mellitus, Experimental , Insulin-Secreting Cells , Adenosine Triphosphate/metabolism , Animals , Blood Glucose/metabolism , Glucose/metabolism , Insulin Secretion , Insulin-Secreting Cells/metabolism , MiceABSTRACT
Strongly oxidative H2O2 is biologically important, but if uncontrolled, would lead to tissue injuries. Lactoperoxidase (LPO) catalyzes the redox reaction of reducing highly reactive H2O2 to H2O while oxidizing thiocyanate (SCN-) to relatively tissue-innocuous hypothiocyanite (OSCN-). SCN- is the only known natural, effective reducing-substrate of LPO; humans normally derive SCN- solely from food. While its enzymatic mechanism is understood, the actual biological role of the LPO-SCN- system in mammals remains unestablished. Our group previously showed that this system protected cultured human cells from H2O2-caused injuries, a basis for the hypothesis that general deficiency of such an antioxidative mechanism would lead to multisystem inflammation and tumors. To test this hypothesis, we globally deleted the Lpo gene in mice. The mutant mice exhibited inflammation and lesions in the cardiovascular, respiratory, digestive or excretory systems, neuropathology, and tumors, with high incidence. Thus, this understudied LPO-SCN- system is an essential protective mechanism in vivo.
Subject(s)
Carcinogenesis/metabolism , Inflammation/metabolism , Lactoperoxidase/deficiency , Neoplasms/metabolism , Animals , Disease Models, Animal , Female , Humans , Hydrogen Peroxide/metabolism , Hydrogen-Ion Concentration , Inflammation/genetics , Inflammation/immunology , Lactoperoxidase/genetics , Male , Mice , Mice, Transgenic , Mutation , Neoplasms/genetics , Neoplasms/immunology , Oxidation-Reduction , Thiocyanates/metabolismABSTRACT
Voltage-gated ion channels underlie rapid electric signaling in excitable cells. Electrophysiological studies have established that the N-terminal half of the fourth transmembrane segment ((NT)S4) of these channels is the primary voltage sensor, whereas crystallographic studies have shown that (NT)S4 is not located within a proteinaceous pore. Rather, (NT)S4 and the C-terminal half of S3 ((CT)S3 or S3b) form a helix-turn-helix motif, termed the voltage-sensor paddle. This unexpected structural finding raises two fundamental questions: does the paddle motif also exist in voltage-gated channels in a biological membrane, and, if so, what is its function in voltage gating? Here, we provide evidence that the paddle motif exists in the open state of Drosophila Shaker voltage-gated K(+) channels expressed in Xenopus oocytes and that (CT)S3 acts as an extracellular hydrophobic 'stabilizer' for (NT)S4, thus biasing the gating chemical equilibrium toward the open state.
