Doerner D, Alger B E
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201.
Brain Res. 1992 Nov 27;597(1):30-40. doi: 10.1016/0006-8993(92)91502-6.
Studies using phorbol esters imply that hippocampal Ca2+ channels are regulated by protein kinase C (PKC); however concerns have been raised because in some circumstances phorbol esters have non-specific effects on ion channels. We have tested the hypothesis that PKC modulates Ca2+ channel activity in hippocampal neurons by conducting a detailed comparison of the effects of the diacylglycerols, diC8 and OAG, with those of the phorbol ester, PDBu, on whole-cell and single-channel Ca2+ currents. Close similarity of action of these different activators would support the hypothesis. We found that, like PDBu, the diacylglycerols (DAGs) suppressed whole-cell Ba2+ current (IBa) in a dose-dependent and reversible manner and caused a hyperpolarizing shift in the voltage dependence of steady-state IBa inactivation. Suppression of IBa by diC8 and OAG was not mimicked by an enzymatically inactive diacylglycerol isomer, EGD. The effects of both PDBu and DAGs could be blocked by a specific peptide inhibitor of PKC, and both types of activator depressed IBa when it was recorded in the nystatin perforated-patch mode. In single-channel recordings, DAGs enhanced L-type Ca2+ channel activity in a manner indistinguishable from that of PDBu. Finally, DAGs as well as PDBu markedly increased spontaneous synaptic activity in tissue-cultured hippocampal neurons. The numerous similarities between the effects of DAGs and PDBu strongly support the general conclusion that PKC mediates the effects of these activators and the specific conclusion that PKC modulates Ca2+ channel activity in hippocampal neurons.
使用佛波酯的研究表明，海马体中的钙离子通道受蛋白激酶C（PKC）调节；然而，由于在某些情况下佛波酯对离子通道有非特异性作用，因此引发了一些担忧。我们通过详细比较二酰基甘油（diC8和OAG）与佛波酯（PDBu）对全细胞和单通道钙离子电流的影响，来检验PKC调节海马神经元钙离子通道活性的假设。这些不同激活剂作用的高度相似性将支持该假设。我们发现，与PDBu一样，二酰基甘油（DAGs）以剂量依赖性和可逆的方式抑制全细胞钡离子电流（IBa），并使稳态IBa失活的电压依赖性发生超极化偏移。酶促无活性的二酰基甘油异构体（EGD）不能模拟diC8和OAG对IBa的抑制作用。PKC的一种特异性肽抑制剂可以阻断PDBu和DAGs的作用，并且当在制霉菌素穿孔膜片钳模式下记录时，这两种类型的激活剂都会抑制IBa。在单通道记录中，DAGs增强L型钙离子通道活性的方式与PDBu无法区分。最后，DAGs以及PDBu显著增加了组织培养的海马神经元中的自发突触活动。DAGs和PDBu作用之间的众多相似性有力地支持了PKC介导这些激活剂作用的一般结论，以及PKC调节海马神经元钙离子通道活性的具体结论。
