The determination of the cellular volume of avian, porcine and bovine phagocytes and bovine mammary epithelial cells and its relationship to uptake of tilmicosin

In order to compare the intracellular concentration of antimicrobial agents in phagocytic and nonphagocytic cells, the knowledge of their cell volume is essential. For the first time, the determination of the avian, porcine, and bovine polymorphonuclear neutrophils (PMN), monocyte-derived macrophage s, macrophages, and bovine mammary epithelial cell volume was performed usi ng [H-3]-water and [C-14]-carboxyinulin, The comparison of all the cells sh owed that the PMN have a size range between 3.58 acid 4.04 mu L per mg of p rotein, and are smaller than the monocyte-derived macrophages and mammary e pithelial cells (4.32-5.01 mu L per mg of protein), The macrophages show th e largest size (5.84-6.57 mu L per mg of protein). The cellular uptake of t ilmicosin in these cells was then determined. The examination of the intrac ellular/extracellular concentration ratios (C-i/C-e) after 4 h of incubatio n with 10 mg/mL of [C-14]-labelled tilmicosin revealed that tilmicosin was well accumulated and showed a ratio of 137, 169 and 193 in avian PMN, porci ne PMN, and bovine alveolar macrophages, respectively, The cellular uptake data also demonstrated that tilmicosin accumulated in nonphagocytic bovine mammary epithelial cells. The importance of the use of the appropriate spec ies and cell type specific cell volume values for calculations was exemplif ied by calculating the C-i/C-e of tilmicosin using cell volume data found i n the literature for human and mouse cells, The subsequent comparison of th ese data with the C-i/C-e calculated with the actual cell volume appropriat e for the species tested revealed an under evaluation of 3-13% in monocyte- macrophages, an over evaluation of 7-18%, 16-31% and 69% in PMN, macrophage s, and epithelial cells, respectively. This study highlights the importance of the proper cell volume in order to determine the C-i/C-e. Moreover, the cell volumes determined here for avian, porcine and bovine cells should fa cilitate further in vitro and in vivo cellular studies by veterinary resear chers.