Ionic mechanism underlying distinctive excitability in atrium and ventricle of the heart / 生理学报

Cellular excitability is an important physiological factor in maintaining normal cardiac activity. The present study was designed to investigate the ionic mechanism underlying different excitability in atrial and ventricular myocytes of guinea pig heart using a whole-cell patch configuration. We found that excitability is lower in ventricular myocytes than that in atrial myocytes. Although the density of voltage-gated fast Na(+) current (INa) was lower in ventricular myocytes, it would not correlate to the lower excitability since its availability was greater than that in atrial myocytes around threshold potential. Classical inward rectifier K(+) current (IK1) was greater in ventricular myocytes than that in atrial myocytes, which might contribute in part to the lower excitability. In addition, the transient outward K(+) current with inward rectification (Itoir) elicited by depolarization was greater in ventricular myocytes than that in atrial myocytes and might contribute to the lower excitability. In ventricular myocytes, Ba(2+) at 5 µmol/L significantly inhibited Itoir, enhanced excitability, and shifted the threshold potential of INa activation to more negative, and the effect was independent of affecting INa. Our results demonstrate the novel information that in addition to classical IK1, Itoir plays a major role in determining the distinctive excitability in guinea pig atrial and ventricular myocytes and maintaining cardiac excitability. More effort is required to investigate whether increase of Itoir would be protective via reducing excitability.

The correlation between personal occupational exposure to soluble chromate and urinary chromium content / 中华预防医学杂志

<p><b>OBJECTIVE</b>To explore and provide the possible biological limit of urinary chromium for population occupationally exposure to soluble chromate, as to providing scientific evidences for health monitoring and risk assessment.</p><p><b>METHODS</b>A cross-sectional study was conducted. The studied population contained 83 workers from different processes of the chromate plant, in addition, 10 farmers without exposure to chromate matched with exposed subjects by age, gender and smoking status were identified as a control group. The air chromium concentration for personal exposure during 8-hours shift and the urinary chromium concentration post-shift were determined and their relationship was analyzed statistically. Meanwhile, the literatures of the biological limit of urinary chromium for occupational exposure to soluble chromate were studied.</p><p><b>RESULTS</b>For the control group, the air chromium concentration had a range from 0.00 microg/m(3) to 0.08 microg/m(3) and the urinary chromium concentration from 0.40 microg/g Cre to 1.02 microg/g Cre. For the exposure group, the air chromium concentration was from 0.10 microg/m(3) to 287.00 microg/m(3) and the urinary chromium concentration was from 1.14 microg/g Cre to 79.07 microg/g Cre. The positive relationship existed in between air chromium concentration and urinary concentration. The urinary chromium concentration was increased depending on the chromate exposed level. The regress equation was that Urinary chromium concentration (microg/g Cre) = 4.16 + 236.86 x air concentration for chromate (mg/m(3)), r = 0.976. The recommendation of ACGIH (USA, 2004) was 65.1 micromol/mol Cre (30 microg/g Cre) with the same TLV-TWA of 0.05 mg/m(3) as our National standard about the air chromate concentration.</p><p><b>CONCLUSION</b>Our findings suggested that the post-shift urinary chromium concentration might be used as an exposed biomarker for chromate. Considering the recommendation of ACGIH (USA, 2004) and the feasibility of the standard performed, we suggest that the biological threshold limit of urinary chromium for occupational exposure to soluble chromate in China should be 65.1 micromol/mol Cre (30 microg/g Cre) (post-shift urine for consecutive 5 work days.).</p>

Chromium content in erythrocytes serving as the exposure biomarker for workers exposed to soluble chromate / 中华预防医学杂志

<p><b>OBJECTIVE</b>To explore biological exposure markers, we investigated the chromium content in peripheral erythrocytes from occupational population with broad ranges of soluble chromate exposure, as the candidate biomarker may provide the scientific evidence for health risk assessment in occupational chromate-exposed population.</p><p><b>METHODS</b>A cross-sectional study was conducted in chromate exposed workers employed at a chromate factory in a district of Jinan city, Shandong Province. The studied population contained 114 workers from different processes of the chromate plants, which included 74 males and 40 females, with an age range from 25 to 52 years old, averaging at (35.83 +/- 6.14) years old; the length of service was ranging from 1 year to 37 years, an average of (14.20 +/- 6.77) years. In addition, 30 farmers in the countryside one hundred kilometers away from the factory, without exposure to chromate matched with exposed subjects by age, gender and smoking status were identified as a control group, which included 22 men and 8 women, with age ranging from 25 years old to 47 years old, having an average age of (36.13 +/- 6.17) years old. Personal information on age, chromate exposure, medical history, smoking habit and alcohol consumption was obtained at an interview. The air concentration of personal exposure was determined by individual sampling for 8 hours per day as shift work, and chromium was assayed by atomic absorption spectrometry. The chromium content in the erythrocytes from peripheral blood was determined by graphite furnace atomic absorption spectrometry. The potential plasma reduction capacity was determined by dibenzene anthracoamid dihydrazide spectrophotometry. The content of total vitamin C and reductive ascorbic acid were determined by 2, 4-dinitrobenzene hydrazine. The data were analyzed by SPSS10.0 software for statistical significance.</p><p><b>RESULTS</b>(1) The results showed that the chromium levels in erythrocytes in the exposed group [(15.79 +/- 31.01) microg/L] were significantly higher than those in the control group [(3.21 +/- 2.20) microg/L] (P < 0.01). (2) There existed a dose-response relationship between the personal airborne chromate concentration and the chromium content in erythrocytes. As airborne chromate concentration lowered to 106.00 microg/m(3), the chromium content in erythrocytes increased, depending on the air concentration of chromate. (3) Correlation analysis showed that there was a significant positive correlation between airborne chromate concentration and the chromium content in erythrocytes (P < 0.01). (4) In multiple regression analysis, it was found that the potential plasma reduction capacity and reductive ascorbic acid may be a good indicator for oxidative stress produced by chromate exposure and be used to evaluate the effects on intracellular uptake of chromium (VI).</p><p><b>CONCLUSION</b>Our findings suggested that the chromium content in erythrocytes should be used as an effective exposed biomarker in the risk assessment for occupational chromate-exposure.</p>

Study on DNA strand breaks in workers exposed to soluble chromate / 中华预防医学杂志

<p><b>OBJECTIVE</b>To explore the biological effective markers, we investigated DNA strand breaks in peripheral lymphocytes from occupational population with broad ranges of soluble chromate exposure.</p><p><b>METHODS</b>We conducted a cross-sectional study in the chromate exposed workers employed at a chromate factory in a district of Jinan, Shandong Province. The studied population contained 114 workers from different processes of the chromate plants, in addition, 30 farmers in the countryside about one hundred kilometers away from the factory, without exposure to chromate were matched with the exposed subjects by age, gender and smoking status being identified as a control group. Personal information on age, chromate exposure, medical history (including acute infection and medicine usage), smoking habit and alcohol consumption was obtained by questionnaire. DNA strand breaks in lymphocytes were detected by single-cell gel electrophoresis assay (comet assay) and the DNA damaged degree was evaluated by the score weighted by comet type. The air concentration of chromate was determined by individual sampling for 8 hours per day as shift work and chromium was assayed by atomic absorption spectrometry. The chromium content in the erythrocytes from peripheral blood was determined by graphite furnace atomic absorption spectrometry. The data were analyzed by SPSS10.0 software for statistical significance.</p><p><b>RESULTS</b>(1) The results showed that the score for DNA strand breaks in lymphocytes were 54.52 +/- 23.51 in the exposed group, which was significantly higher than those in the control group (24.70 +/- 11.84) (P < 0.01). (2) The degree of DNA strand breaks in lymphocytes was increased in a dose-dependent manner ranging from 0 microg/m(3) to 106.00 microg/m(3). (3) Correlation analysis showed that there was a significant positive correlation between airborne chromate concentration and the degree of DNA strand break in lymphocytes (P < 0.01). (4) By multiple regression analysis, it was found that the airborne concentrations, chromium contents in red blood cells and smoking habits were factors which might affect the degree of DNA breaks.</p><p><b>CONCLUSION</b>Our findings suggest that DNA strand break in lymphocytes should be an effective biomarker for occupational chromate-exposed population and be applied in biological monitoring and health risk assessment for occupational chromate-exposed population.</p>