The Journal of Neurophysiology Vol. 84 No. 5 November 2000, pp. 2291-2301
Copyright ©2000 by the American Physiological Society

Analysis of Single K_ATP Channels in Mammalian Dentate Gyrus Granule Cells

 ¹Bloorview Epilepsy Research Laboratory, Division of Cellular and Molecular Biology, Toronto Western Research Institute; and Departments of  ²Physiology, Medicine ( ³Neurosurgery,  ⁴Neurology), and  ⁵Pharmaceutical Science, University of Toronto, University Health Network, Toronto, Ontario M5T 2S8, Canada

Pelletier, Marc R., Peter A. Pahapill, Peter S. Pennefather, and Peter L. Carlen. Analysis of Single K_ATP Channels in Mammalian Dentate Gyrus Granule Cells. J. Neurophysiol. 84: 2291-2301, 2000. ATP-sensitive potassium (K_ATP) channels are heteromultimer complexes of subunits from members of the inwardly rectifying K⁺ channel and the ATP-binding cassette protein superfamilies. K_ATP channels couple metabolic state to membrane excitability, are distributed widely, and participate in a variety of physiological functions. Understood best in pancreatic  cells, where their activation inhibits insulin release, K_ATP channels have been implicated also in postischemia cardio- and neuroprotection. The dentate gyrus (DG) is a brain region with a high density of K_ATP channels and is relatively resistant to ischemia/reperfusion-induced cell death. Therefore we were interested in describing the characteristics of single K_ATP channels in DG granule cells. We recorded single K_ATP channels in 59/105 cell-attached patches from DG granule cells in acutely prepared hippocampal slices. Single-channel openings had an E_K close to 0 mV (symmetrical K⁺) and were organized in bursts with a duration of 19.3 ± 1.6 (SE) ms and a frequency of 3.5 ± 0.8 Hz, a unitary slope conductance of 27 pS, and a low, voltage-independent, probability of opening (P_open, 0.04 ± 0.01). Open and closed dwell-time histograms were fitted best with one (_open = 1.3 ± 0.2 ms) and the sum of two (_closed,fast = 2.6 ± 0.9 ms, _closed,slow = 302.7 ± 67.7 ms) exponentials, respectively, consistent with a kinetic model having at least a single open and two closed states. The P_open was reduced ostensibly to zero by the sulfonylureas, glybenclamide (500 nM, 2/6; 10 µM,11/14 patches) and tolbutamide (20 µM, 4/6; 100 µM, 4/4 patches). The blocking dynamics for glybenclamide included transition to a subconductance state (43.3 ± 2.6% of control I_{open channel}). Unlike glybenclamide, the blockade produced by tolbutamide was reversible. In 5/5 patches, application of diazoxide (100 µM) increased significantly P_open (0.12 ± 0.02), which was attributable to a twofold increase in the frequency of bursts (8.3 ± 2.0 Hz). Diazoxide was without effect on _open and _closed,fast but decreased significantly _closed,slow (24.4 ± 2.6 ms). We observed similar effects in 6/7 patches after exposure to hypoxia/hypoglycemia, which increased significantly P_open (0.09 ± 0.03) and the frequency of bursts (7.1 ± 1.7 Hz) and decreased significantly _closed,slow (29.5 ± 1.8 ms). We have presented convergent evidence consistent with single K_ATP channel activity in DG granule cells. The subunit composition of K_ATP channels native to DG granule cells is not known; however, the characteristics of the channel activity we recorded are representative of Kir6.1/SUR1, SUR2B-based channels.