Expression of sulphonylurea receptors in bovine monocytes from animals with a different metabolic rate

The aim of this study was to investigate the relationship between expression of sulphonylurea receptors (SUR) and metabolic rate (MR). SUR on monocytes and cells from muscle tissue were detected using fluorescent glibenclamide and flow cytometry. Transmembrane potential differences were detected by oxonol dye fluorescence measurements. A bovine model was used to induce differences in the MR by exposure to different ambient temperatures (4 degrees C and 18 degrees C), by different feeding levels (1.0- and 1.6-fold the metabolizable energy requirement for maintenance) and by alpha2-adrenergic stimulation. We found that cells from skeletal muscle (m. semimembranosus), immunochemically identified as smooth muscle cells, skeletal muscle fibres and monocytes, responded in comparable fashions to glibenclamide and ATP, i.e. with a depolarization, and to cromakalim with a polarization, suggesting that monocytes are useful indicators of regulatory events occurring in muscle cells. Glibenclamide fluorescence was assumed to represent SUR associated with KATP channels. Significant differences were detected in the percentage of depolarized monocytes in the different variants of the model. A linear correlation between monocytes that bound fluorescent glibenclamide and the MR was evident (with a coefficient of determination of 0.94) and was reproducible following reduction of the MR, by alpha2-adrenergic stimulation, suggesting that expression is involved in the regulation of whole-body energy expenditure.