Engisch K L, Wagner J J, Alger B E
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA.
Hippocampus. 1996;6(2):183-91. doi: 10.1002/(SICI)1098-1063(1996)6:2<183::AID-HIPO8>3.0.CO;2-Q.
Muscarinic, cholinergic inputs, largely from the medial septum, have pronounced effects on hippocampal cell excitability. A major effect of synaptically released ACh is block of the slow Ca(2+)-dependent potassium current, called IAHP. Protein kinase C exists in the hippocampus in high concentrations, its activation blocks IAHP, and it has been suggested as a mediator of the muscarinic-receptor-(mAChR)-mediated actions. Using conditions that produce a stable postspike afterhyperpolarizing current (IAHP) in whole-cell recordings from CA1 hippocampal pyramidal neurons in the slice preparation, we have investigated the role of PKC in the cholinergic inhibition of IAHP mediated by mACHRs. Bath application of the general kinase inhibitor, H7, had no effect on inhibition of IAHP by carbachol, although H7 dramatically reduced inhibition of IAHP by the phorbol ester, phorbol-12, 13-diacetate (PDA). Another muscarinic response thought to be mediated by PKC-inhibition of GABAB-mediated hyperpolarization-was reduced by extracellular H7 treatment, suggesting that the coupling between mAChRs and protein kinase activity was maintained in whole-cell recordings. We also discovered that PDA does not mediate its effects on IAHP directly. Intracellular perfusion of high concentrations of H7 (10 mM) or the specific PKC inhibitor, PKCI(19-31) (1 mM), did not prevent inhibition of IAHP by PDA. These results are consistent with an indirect, presynaptic action of phorbol esters on IAHP, possibly mediated through enhanced release of neurotransmitter from surrounding cells.
毒蕈碱能胆碱能输入主要来自内侧隔区，对海马细胞兴奋性有显著影响。突触释放的乙酰胆碱（ACh）的一个主要作用是阻断缓慢的钙依赖性钾电流，即IAHP。蛋白激酶C在海马中高浓度存在，其激活可阻断IAHP，并且有人提出它是毒蕈碱受体（mAChR）介导作用的介质。利用在脑片制备中从CA1海马锥体神经元进行全细胞记录时产生稳定的锋后超极化电流（IAHP）的条件，我们研究了蛋白激酶C在由mAChRs介导的IAHP胆碱能抑制中的作用。浴加通用激酶抑制剂H7对卡巴胆碱抑制IAHP没有影响，尽管H7显著降低了佛波酯佛波醇-12,13-二乙酸酯（PDA）对IAHP的抑制作用。另一种被认为由蛋白激酶C抑制GABAB介导的超极化所介导的毒蕈碱反应，经细胞外H7处理后减弱，这表明在全细胞记录中mAChRs与蛋白激酶活性之间的偶联得以维持。我们还发现PDA并非直接介导其对IAHP的作用。细胞内灌注高浓度的H7（10 mM）或特异性蛋白激酶C抑制剂PKCI(19 - 31)（1 mM）并不能阻止PDA对IAHP的抑制作用。这些结果与佛波酯对IAHP的间接突触前作用一致，可能是通过增强周围细胞神经递质的释放介导的。
