Intracellular signalling pathways modulate K-ATP channels in inspiratory brainstem neurones and their hypoxic activation: involvement of metabotropic receptors, G-proteins and cytoskeleton

Abstract

K-ATP channels regulate the neuronal excitability and their activation during hypoxia/ischemia protect neurons. The activation of K-ATP channels during hypoxia is assumed to occur mainly due to the fall in intracellular ATP levels, but other intracellular signalling pathways can be also involved. We measured single K-ATP channel currents in inspiratory brainstem neurones of neonatal mice. The activity of K-ATP channels was enhanced in hypoosmotic bath solutions, or after applying negative pressure to the recording pipette. Cytochalasin B activated K-ATP, channels and prevented the effects of osmo-mechanical stress, indicating that cytoskeleton rearrangements, which occur during hypoxia, contribute to the activation of K-ATP channels. During hypoxia, extracellular levels of many neurotransmitters increase, leading to activation of corresponding metabotropic receptors that can modulate KA-rp channels. K-ATP channels were activated by GABA, agonist, baclofen, by mGLUR2/3 agonists and were inhibited by mCLUR1/5 agonists. K-ATP channels were activated by phorbol esters and were inhibited by staurosporine. These treatments did not occlude the modulating actions of mGLUR agonists, indicating that they are not mediated by protein kinase C. Activator of alpha-subunits of G-proteins Mas 7 increased and their inhibitor GPant-2 decreased the activity of K-ATP channels. In the presence of either agent, the modulatory actions of baclofen and mGLUR agonists were not observed. We conclude that K-ATP channels are modulated by G-proteins that are activated by metabotropic receptors for GABA and glutamate and their release during hypoxia complements activation of channels by osmo-mechanical stress and [ATP], depletion. (C) 2000 Elsevier Science B.V. All rights reserved.