Effect of melatonin on phagocytic activity and intracellular free calcium concentration in testicular macrophages from normal and streptozotocin-induced diabetic rats

摘要

This study examined the effect of melatonin (MLT) on in vitro phagocytosis of testicular macrophages taken from control and streptozotocin (STZ)-induced diabetic rats and the possible mechanism of its action. The phagocytic activity was measured as a number of latex beads ingested by 100 macrophages ( PI, phagocytic index) in consecutive time points of the incubation. Changes in intracellular free calcium level [Ca2+](i) in isolated macrophages in vitro were measured with the use of ratio-image fluorescence microscopy ( fluorescent dye: Fura2/AM). Phagocytic index in macrophages isolated from healthy rats was 20% higher than in those from diabetic animals. Melatonin in physiological concentration ( 10(-7) M) significantly ( p < 0.05) increased the PI in testicular macrophages from control animals ( PI = 68 +/- 5 with MLT compared to PI = 46 +/- 7 without MLT) while no such effect was observed in the cells from diabetic rats ( PI = 36 +/- 23 with MLT compared to PI = 31 +/- 11 without MLT). Basal [Ca2+](i) was significantly ( p < 0.01) higher in macrophages from diabetic rats compared to control. Stimulation of both control and diabetic testicular macrophages with 10(-7) M MLT resulted in a significant ( p < 0.05) increase in [Ca2+](i) in cells incubated in 2.5 mM calcium solution while no such response was observed in calcium-free Tyrode solution. However, MLT evoked [Ca2+](i) response in macrophages isolated from diabetic animals was much lower than in macrophages isolated from age-matched controls and the time needed for maximal response was much longer. Lack of response in calcium-free solution suggests that extracellular calcium may be necessary to trigger MLT response and in its progression.