Analysis of single K(ATP) channels in mammalian dentate gyrus granule cells.
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 beta 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 (tau(open) = 1.3 +/- 0.2 ms) and the sum of two (tau(closed,fast) = 2.6 +/- 0.9 ms, tau(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 microM,11/14 patches) and tolbutamide (20 microM, 4/6; 100 microM, 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 microM) 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 tau(open) and tau(closed,fast) but decreased significantly tau(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 tau(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.
Pelletier
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MR
Bloorview Epilepsy Research Laboratory, Division of Cellular and Molecular Biology, Toronto Western Research Institute, University of Toronto, University Health Network, Toronto, Ontario M5T 2S8, Canada.
Pahapill
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Pennefather
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Carlen
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D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D018891:Dentate Gyrus / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D003981:Diazoxide / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D007003:Hypoglycemia / Q000503:physiopathology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D000860:Hypoxia / Q000503:physiopathology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008297:Male; D008322:Mammals; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000737:chemistry* / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D017208:Rats, Wistar; D014044:Tolbutamide / Q000494:pharmacology
D000959:Antihypertensive Agents; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D014044:Tolbutamide; D003981:Diazoxide; D005905:Glyburide