Effects Of Acetylcholinesterase Inhibitors And Metal Ions On Ion Channels In Hippocampal Neurons Of Rats

Alzheimer's disease (AD) is a progressive type of senile dementia affecting a large number of the elderly population. It is recognized as a major public health problem having a severe impact on human beings. A deficiency in cholinergic neurotransmission is considered to be one of the major causes of memory impairments in patient. It was hypothesized that the cognitive loss associated with Alzheimer's disease was related to reduction of acetylcholine (ACh) and central cholinergic deficit. Thus, increasing ACh by acetylcholinesterase (AChE) inhibitors might enhance cognitive function in AD patients. Furthermore, central potassium channels play important roles in regulation of learning and memory. Several AChE inhibitors have been found effective on central outward potassium currents. On the basis of studying the influence of 3-benzidino-6(4-chlorophenyl) pyridazine (BCP), 3-benzidino-5 -methyl-6-phenylpyridazine (BMP) and 3-benzidino-6- phenylpyridazine (BPP) on electric eel AChE, We studied the effects of these three compounds on delayed rectifier outward potassium current (I_K) and transient outward potassium current (I_a) in acutely isolated rat hippocampal pyramidal neurons by whole-cell patch-clamp technique. The results show as below:Outward potassium currents in acutely isolated rat hippocampal pyramidal neurons were recorded by whole cell patch-clamp technique. (1) BCP inhibited I_A and I_K in a concentration-dependent and voltage-dependent manner, while BMP and BPP inhibited I_A and I_K in a concentration-dependent manner;sequence of blockade on I_A was: BPP>BCP?BMP;sequence of blockade on I_K was: BPP?BMP>BCP;when we substituted methyl and chloride in the 5-position of the pyridazine ring and in the 4-position of the phenyl ring for the hydrogen atom, respectively, the inhibition effect was weaker. (2) The kinetics of blockade of these three compounds on I_A and I_K indicated that the activation curve for I_A and I_K was shifted by BCP in the depolarizing direction as that for the inactivation curve for I_A, and that the activation curve for I_A and I_K was shifted by BMP to left as that for theinactivation curve for 7A, and that only the inactivation curve for 7A was shifted by BPP to left. (3) The activation and inactivation time constants of 7A and 7K increased in the presence of BCP at different concentration in extracellular solution;The activation and inactivation time constants of 7A decreased in the presence of BMP at different concentration in extracellular solution;The activation time constants of 7A and 7K increased and inactivation time constants of 7A decreased in the presence of BPP at different concentration in extracellular solution. (4) Our results supported the proposition that the action of AChE inhibitors may be related to potassium channels. The IC50 value of BCP and BMP towards 7K and 7A in this study was slightly higher than that of BCP and BMP towards AChE on electric eel. It suggested that BCP and BMP appeared to be more sensitive to AChE than to these two kinds of currents and AChE could be major action site of BCP and BMP. However, potassium channels might still be other new targets for BCP and BMP besides AChE. (5) Effects of BPP, BCP and BMP on the 7K and 7A were not identical. Effects of BPP, BCP and BMP on the 7K and 7A were not markedly related to chemical structures of these three compounds.One of major pathological signs of AD is p-amyloid plaques. Zinc and copper are essential trace metals. Content Of copper and zinc are so high to induce accumulation of Ap\ We studied the effects of copper and zinc on 7K and 7A in acutely isolated rat hippocampal pyramidal neurons by whole-cell patch-clamp technique. The results show as below:Outward potassium currents and inward sodium currents in acutely isolated rat hippocampal pyramidal neurons were recorded by whole cell patch-clamp technique. (1) Zinc inhibited 7A and 7K in a concentration-dependent and voltage-dependent manner. Blocking effect of zinc on 7A and 7K became stronger and stronger with changes of membrane potential from negative to positive. The kinetics of blockade of zinc on 7A and 7K indicated that the activation curves and inactivation curves for 7A and 7K were shifted by zinc in the negative voltage direction. (2) Effect of copper on 7A and 7K was relative to concentration. When concentration was lower than 10 or 20uxnol/L, 7A and 7K increased, increasing ratio decreased with increasing copper concentration in the bath solutions. Copper increased 7A and JK in a voltage-dependent manner, too. Increasing effect of copper on 7A and 7K became weaker and weaker with changes of membrane potential from negative to positive. The kinetics of increase effect of copper on 7A and 7k indicated that the activation curves and inactivation curves for7A were shifted by copper in the negative voltage direction, and that the activation curves for 7K were shifted by copper in the positive voltage direction. When concentration was more than 20 or 50 umol/L, 7A and 7k decreased, inhibited ratio increased with increasing copper concentration in the bath solutions. Copper decreased 7A in a voltage-dependent manner, too. Decreasing effect of copper on 7A became stronger and stronger with changes of membrane potential from negative to positive. The kinetics of decrease of copper on 7A and 7K indicated that the activation curves for 7K were shifted by copper in the negative voltage direction. (3) Lanthanum inhibited 7A in a concentration-dependent and voltage-dependent manner. Blocking effect of lanthanum on 7A became stronger and stronger with changes of membrane potential from negative to positive. The kinetics of blockade effect of lanthanum on 7A and 7K indicated that the activation curves and inactivation curves for 7A were shifted by BCP in the negative voltage direction. (4) Zinc inhibited 7Na in a concentration-dependent manner, while copper and lanthanum increased 7Na in a concentration-dependent manner.