Voltage-dependent delayed rectifier K؉ channels regulate aspects of both stimulus-secretion and excitationcontraction coupling, but assigning specific roles to these channels has proved problematic. Using transgenically derived insulinoma cells (TC3-neo) and -cells purified from rodent pancreatic islets of Langerhans, we studied the expression and role of delayed rectifiers in glucose-stimulated insulin secretion.
In the present study, we investigated the effect of Ginkgo biloba extract, EGb 761, and one of its components, bilobalide, on gene expression of subunit 1 of mitochondrial NADH dehydrogenase (ND1) in PC12 cells. By Northern blot analysis we found a approximately 2-fold significant increase in NDI mRNA level, after 48 and 72 h exposure to 100 microg/ml EGb 761 and to 10 microg/ml bilobalide. We also evaluated, by oxygraphy measurements, mitochondrial respiration during state 3 and state 4. In cells treated with EGb 761 and bilobalide for 48 and 72 h, state 4 respiration was significantly decreased, and the respiratory control ratio was increased. These results provide evidence that EGb 761 and bilobalide exert their protective effects by up-regulating mitochondrial ND1 gene expression and by decreasing state 4 respiration, whose increase is thought to be responsible for oxidative damage.
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