| ObjectiveLead has high affinity to nerve, and it can be accumulated in nerve tissue, which causes the long-period damage to nerve system, major to the memory and learning. As is known that lead can interfere the formation and maintain of LTP, the activity of PKC in hippocamp and the distribution of isoenzymes PKC-γby abnormally enhancing or inhibiting the activity of PKC.The covalent modification of protein is one of the major ways to regulate enzymes and active proteins in the process of signal transduction. Phosphorylation is the most common and important modification, which is completed by protein kinase (PK). More than 400 PK has been found, and it is still difficult to say how many kinds of PK exactly. Mitogen-activated protein kinase (MAPK) is a newly found family of PK, including three subfamilies: ERK1/2, JNK/SAPK and p38MAPK. ERK1/2 major takes action in the process of the growth, mitosis and differentiation of cells; JNK/SAPK and p38MAPK, in the process of inflammation and stress. We studied the effect of chronic lead-exposure on the signal transduction in nerve system.ERK1/2 affects the formation and maintain of LTP by activating CREB. It is reported that lead affects the ability of memory through CREB and LTP. But few reports prove whether lead affects memory by the signal transducting way of ERK1/2 or not. Our experiment interests in it, especially about the effect of different lead concentration on the regularity of ERK in different developing period.Methods1 Chronic exposure to lead:Divided the mice into several groups on the 7th day after they had mated, and fed them with water containing different lead concentration, 2.4 mmol/l, 4.8 mmol/l, 9.6mmool/l, respectively. The control group was fed with tap water. After breast feeding, fed their descendents with the same water, then killed them on the 1st, 7th, 14th, 21nd, 28th, 35th after birth, respectively, and took out of the brains, stored at -70℃. 2 Prepare the samples:Took out the samples, added the buffer (NaCl 0.1mol/l, TrisCl 0.01mol/l, PH 7.6, EDTA 0.001mol/l, PH 8.0, PMSF 100μg/ml), then shattered by ultrasound, centrifuged at 27000G for lhour at 4℃, moved the fluid phase into a new tube. Measured the content of protein by Lowery method.3 The expression of ERK1/2, PKC-γwere determined by westem blots.Results1 Effect on the activity of PKC-γThe activity of PKC-γincreased gradually at the late developing stage, and rose sharply on the 14th day, reached the peak on the 21 nd day, then decreased quickly until the35th day, when the activity almost turned back to the level at birth or lower.Compared to the control, groups of brains treated with different concentration of lead showed a graph of different cytoplasmic activity of PKC-γ. Most of the group reached the peak at 21d. After 21d, the activity of PKC-γdecreased when treated with lead of low concentration and also decreased with high concentration of lead.2 The expression of ERK under the effect of different lead concentrationDuring the period of 7d～14d, all the expression level of ERK in lead exposed group was almost the same with that of the control, while during the period 21d-28d, the difference appeared. In group of 2.4mmol/l, nearly normal level; in group of 4.8mmol/l, lower, and much lower in the latter group; in group of 9.6mmol/l, the expression level reduced apparently, the peak value appeared at 14d.Conclusions1 The higher the lead concentration is, the more damage can be caused.2 Lead influences the expression of ERK apparently during the 21 nd day, low lead concentration will result in the increase of expression, while the high concentration, the decrease. |
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