The Modulation Effect Of Vascular Endothelial Growth Factor On Ion Channels In Rat Hippocampal Neurons And Its Mechanism

Vascular endothelial growth factor (VEGF) is a dimeric glycoprotein and widely expressed in neurons besides vascular endothelial cells in the adult rat brain. Previous studies reported that VEGF had neuroprotective role, in addition to its ability to increase vascular permeability and potent angiogenic activity. However, the protective mechanism remains unclear. Recent studies suggested that several growth factors could acutely modulate ion channels. Does VEGF have the same effect? Is this mechanism related to its neuroprotective action? To answer these questions, in this experiment, the expression of VEGF receptors was measured by immunohistochemical technique, the effect of VEGF on ion channels was investigated in neurons acutely isolated from rat hippocampus by whole-cell patch clamp technique.Immune-fluorescence double staining results showed that VEGF receptors flt-1 were expressed on acutely isolated hippocampal neurons, but there was no expression of VEGF receptors flk-1 on the same cells studied.The electrophysiological results showed that a local application of VEGF (lOOng/ml) could decrease the frequency of action potential and prolong the repolarization duration. It down-regulated voltage gated sodium channel, but didn't affect steady-state inactivation of the channel. VEGF could significantly reduce IK in rapid, partially reversible and voltage-dependent manners. Intracellular injection of Lucifer yellow combined with immunohistochemical staining for VEGF receptors flt-1 showed that cells which had the decreased potassium currents to VEGF application expressed VEGF receptors flt-1 , whereasthe cells without VEGF receptors flt-1 expression didn't have this biological effect. The inhibitory effect of VEGF on IK was abolished by genistein, a specific tyrosine kinase inhibitor, which suggested that this effect might be related to the stimulation of the activity of this kinase. We further studied the effect of VEGF on IK in hippocampal neurons isolated from the rat brain following middle cerebral artery occlusion (MCAO). The results showed that VEGF also could reduce IK in the ischemic injured neurons.From above studies, we concluded that VEGF could decrease the frequency of action potential and prolong the repolarization duration; down-regulate voltage gated sodium channels; decrease IK and regulate neuronal excitability. The mechanism of this modulation effect might be related to flt-1 receptor via the stimulation of its tyrosine kinase activity.