| Background Drowning is defined as death due to submersion in liquid. It prevents the exchange of oxygen. According to some surveys, people died from drowning reached 3.5/100,000 one year. Drowning ranked the second cause of accidental deaths among young people. There are many drowning cases which happen in some place in our country each year, especially in the district by the sea or by the river. The statistics of some provinces showed that 20% of autopsies were about drowning each year, some of which were homicidal cases with the corpses thrown into water. Therefore, in order to determine whether the person is drown to death or thrown into water after death, checking and studying the corpses found in water is necessary and plays a key role in deciding the nature of the case.At present, the diagnosis and mechanism of drowning exist some problem according to some phenomenon of the corpse. Because these phenomena can only be observed in a few typical cases and some could be even observed shortly after death Therefore, some problems of this subject are being studed till now. Lab tests, such as diatomic test in the tissue, can provide an important conference for judging drowning, but there are false positive and false negative possibilities. The other tests, such as finding foreign particles test in the lung, the change of the density of ions in the blood, are still in the experimental stage and can not be put into practice soon. The mechanism of drowning is not clear. There are several hypotheses, such as theory of asphyxia death, theory of electrolyte disorder death, theory of cardiac death caused by neural reflection.In order to satisfy the urgent need of forensic practice and elucidate the specific mechanism of drowning, it is quite necessary to take advantage of the scientific and technological achievements, especially theories and technologies of the molecular biology, to study and research drowning. The discovery and related research achievements of Aquaporins have provided a better way to study drowning.The first water channel protein isolated was the aquaporin(AQP) by Agre in 1988, now known as AQP-1. Since then, about ten AQP types have been isolated (AQP0~AQP9). The molecular size of AQPs is about 30kD. It has six trans-membrane domains separated by five connecting loops (A-E). The NH2-and COOH-terminal halves of the polypeptide are sequence-related, and each contains the motif Asn-Pro-Ala. AQPs confer a ten-fold or hundred-fold increase of osmotic water permeability, lack of permeability for protons or other ions, and without Arrhenius activation energy. AQP-1 localizes in lungs, but there are different opinions about which cells AQP-1 localizes.Objective To explore the location of AQP-1 in lungs. To study the expression of AQP-1 in model drowning rats. To study the role of AQP-1 in interpreting the mechanism of drowning.Methods The test included two experimental steps. First step was animal experiment, the animal was rat (Provided by West China Experimental Animal Center, Sichuan University). The experimental rats were divided into three groups, drowning group, control group I and control group II respectively. The drowning group rats were drown to death by immerged into tap water. The rats in other two groups were killed by femoralartery-cutting. Then the dead rats of Control group I were thrown into water, control group II was on land. Immunohistochemistry,Transmission electron micro-scopy, Immunoelectron microscopy and RT-PCR were used to explore the expression and location of the AQP-1.Image analysis was used to measure the IOD (Intergrated optical density). SPSS was used to evaluate the statistical value of IOD The second step was to estimate the value of AQP-1 in forensic practice.Result Immunohistochemistry: The positive expression of AQP-1 was seen in the alveolar cells, bronchial epitheliocytes, and capillary endotheliocytes of the lung. The positive expression of AQP-1 in drowning group was higher than in other experimental groups. Its IOD value of image analysis was statistical significant between drowning group and other two experimental groups.Transmission electron microscopy: The swelling mitochondrions of alveolar cells in drowning group were found.Immuno-electron microscopy: Colloidal gold was seen in the membrane of type I alveolar cells, blood vessel endotheliocytes of the lung and secretory vacuoles of type II alveolar cells in drowning group. The quantity of colloidal gold in the membrane of type I alveolar cells , blood vessel endotheliocytes of drowning rats was higher than other two experimental groups. The quantity was statistical significant between drowning group and other experimental groups. The quantity was no statistical significant between two control groups.RT-PCR: The result of agarose gel electrophoresis was measured by image analysis. Its IOD value was statistical significant between drowning group and other two experimental groups.Conclusion AQP-1 was located in the type I alveolar cells, bronchial epitheliocytes, capillary endotheliocytes of the lung and type II alveolar cells of drowning rats. A great quantity of water was transported by AQP-1. AQP-1 plays akey role in the course of drowning. The positive expression of AQP-1 was statistical significant between drowning group and other two experimental groups. It suggested that AQP-1 positive reaction was one of sensitive signs of drown. It is possible to regulate AQP-1 by the way of long efficency control, short efficency control and degraded enyme as well as by secreting. |
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