Properties Of K_atp Channel In Hippocampal Ca1 Pyramidal Neurons Of Adult Rat And Its Role In The Ischemia-induced Neuronal Injury

ATP-sensitive K~ channels play an important role in coupling membrane excitability with intracellular metabolic stress. In neurons, the question of whether KATP channels are active under normal physiological conditions remains controversial. However, it is accepted that KATP channels can be opened when metabolism is inhibited by conditions such as hypoxia and ischemia, and the changes of KATP channels can affect the electrical activity and excitability of cell membrane and then, provide neuroprotection on the damaged neurons. Little is known about the single channel properties of KATP channels in hippocampal neurons and even in these reports there were a lot of inconsistencies about the properties too. All the information of hippocampal KATP channels was obtained from cultured neurons, and there is no report concerning properties of KATP channels in hippocampal CAl pyramidal neurons from adult rat so far. CAl pyramidal neurons in hippocampus die two to three days after transient cerebral ischemia. The mechanism of this delayed cell deaths are not clear. It has been hypothesized that a progressive suppression of excitability of CAl pyramidal neurons after severe forebrain ischemia may be an important factor involved in the delayed neuronal death. The mechanism of the decrease in neuronal excitability after ischemia may be due to an increase in potassium channel activity. In consistence, it was reported that exposure to the KATP channel opener cromakalim could induce typical apoptosis in culture neurons. All these suggest that the changes in KATP ?? channel activity may contribute to delayed neuronal death. To address this question, we studied the properties of KATP channels in acutely dissociated hippocampal CA 1 pyramidal neurons of adult rats with inside-out configuration of patch clamp techniques firstly, and then, by using the four-vessel occlusion model, we investigated changes of KATP channel activity in CA 1 pyramidal neurons of rat hippocampus after transient forebrain ischernia. Lastly, we examined the effects of tolbutamide, a KATP channel blocker, on damage of hippocampal CAl pyramidal neurons following 15 mm of forebrane ischemia. 1. Properties of KATP channels in hippocampal CAl pyramidal neurons from adult rat. Two types of currents blocked by internal ATP and selectively permeable to were identified in adult CAl neurons. One of them was + identified as classical KATP channel. With symmetrical l4Ommol/L K on both side of the excised membrane, the single-channel conductance was approximately 63pS and the reversal potential was 1.71 mV. These channels had a weakly inward rectifying property. Channels?openings ifltelTupted by shorter closed intervals were more frequently observed at negative holding potential than at positive holding potential. However, noticeably voltage dependence was not found in channel open probability. ATP applied at the cytosolic side inhibited channel activity in a concentration-dependent manner with an IC50 of O.lmmol/L. Sulfonylurea tolbutamide (lmmol/L), a specific KATP channel blocker, added to the bath completely suppressed the channel activity while diazoxide (lmmol/L), a KATP channel opener, had no apparent effect on the current. External TEA (2mmol/L) reduced the amplitude of single-channel current and open probability of KATP channel but couldn抰 block channe...