Bioenergetic and volume regulatory effects of mitoKATP channel modulators protect against hypoxia-reoxygenation induced mitochondrial dysfunction

Abstract

The mitochondrial ATP sensitive K+ channel (mitoKATP) plays a significant role in mitochondrial physiology and protects against ischemic reperfusion injury in mammals. Although fish frequently face oxygen fluctuations in their environment the role of mitoKATP channel in regulating the responses to oxygen stress is rarely investigated in this class of animals. To elucidate if and how mitoKATP channel protects against hypoxia-reoxygenation (H-R)-induced mitochondrial dysfunction in fish, we first determined the mitochondrial bioenergetic effects of two key modulators of the channel, diazoxide and 5-hydroxydecanoate (5-HD), using a wide range of doses. Subsequently, the effects of low and high doses of the modulators on mitochondrial bioenergetics and volume under normoxia and after H-R using buffers with and without magnesium and ATP (Mg-ATP) were tested. In the absence of Mg-ATP (mitoKATP channel open) both low and high doses of diazoxide improved mitochondrial coupling but only the high dose of 5-HD reversed post H-R coupling enhancing effect of diazoxide. In the presence of Mg-ATP (mitoKATP channel closed) diazoxide at low dose improved coupling post H-R and this effect was abolished by 5-HD at low dose. Interestingly, both low and high doses of diazoxide reversed H-R-induced swelling under mitoKATP channel open conditions but this effect was not sensitive to 5-HD. Under mitoKATP channel closed conditions diazoxide at low dose protected the mitochondria from H-R-induced swelling and 5-HD at low dose reversed this effect. In contrast, diazoxide at high dose failed to reduce the swelling caused by H-R and the addition of high dose of 5-HD enhanced mitochondrial swelling. Overall our study showed that in the presence of Mg-ATP both opening of mitoKATP channels and bioenergetic effects of diazoxide were protective against H-R in fish mitochondria, while in the absence of Mg-ATP only the bioenergetic effect of diazoxide was protective.