Glucose and hippocampal neuronal excitability: Role of ATP-sensitive potassium channels

Hyperglycemia-related neuronal excitability and epileptic seizures are not uncommon in clinical practice. However, their underlying mechanism remains elusive. ATP-sensitive K+ (K-ATP) channels are found in many excitable cells, including cardiac myocytes, pancreatic P cells, and neurons. These channels provide a link between the electrical activity of cell membranes and cellular metabolism. We investigated the effects of higher extracellular glucose on hippocampal K-ATP channel activities and neuronal excitability. The cell-attached patch-clamp configuration on cultured hippocampal cells and a novel multielectrode recording system on hippocampal slices were employed. In addition, a simulation modeling hippocampal CA3 pyramidal neurons (Pinsky-Rinzel model) was analyzed to investigate the role of K-ATP channels in the firing of simulated action potentials. We found that incremental extracellular glucose could attenuate the activities of hippocampal K-ATP channels. The effect was concentration dependent and involved mainly in open probabilities, not single-channel conductance. Additionally, higher levels of extracellular glucose could enhance neuropropagation; this could be attenuated by diazoxide, a K-ATP channel agonist. In simulations, high levels of intracellular ATP, used to mimic increased extracellular glucose or reduced conductance of K-ATP channels, enhanced the firing of action potentials in model neurons. The stochastic increases in intracellular ATP levels also demonstrated an irregular and clustered neuronal firing pattern. This phenomenon of K-ATP channel attenuation could be one of the underlying mechanisms of glucose-related neuronal hyperexcitability and propagation. (c) 2007 Wiley-Liss, Inc.