Functional fluorescent Ca2+ indicator proteins in transgenic mice under TET control.

Genetically encoded fluorescent calcium indicator proteins (FCIPs) are promising tools to study calcium dynamics in many activity-dependent molecular and cellular processes. Great hopes-for the measurement of population activity, in particular-have therefore been placed on calcium indicators derived from the green fluorescent protein and their expression in (selected) neuronal populations. Calcium transients can rise within milliseconds, making them suitable as reporters of fast neuronal activity. We here report the production of stable transgenic mouse lines with two different functional calcium indicators, inverse pericam and camgaroo-2, under the control of the tetracycline-inducible promoter. Using a variety of in vitro and in vivo assays, we find that stimuli known to increase intracellular calcium concentration (somatically triggered action potentials (APs) and synaptic and sensory stimulation) can cause substantial and rapid changes in FCIP fluorescence of inverse pericam and camgaroo-2.

Regulation of transferrin-induced endocytosis by wild-type and C282Y-mutant HFE in transfected HeLa cells.

The hereditary hemochromatosis protein HFE is known to complex with the transferrin receptor; however, its function regarding endocytosis of transferrin is unclear. We performed patch-clamp capacitance measurements in transfected HeLa cells carrying wild-type or C282Y-mutant HFE cDNA under the control of a tetracycline-sensitive promoter. Whole cell experiments in cells with suppressed expression of wild-type HFE revealed a decrease in membrane capacitance, reflecting predominance of endocytosis in the presence of transferrin. Cells overexpressing C282Y-mutant HFE displayed less intense capacitance decreases, whereas no significant decrease was observed in cells overexpressing wild-type HFE. The formation of single endocytic vesicles in cells with suppressed expression of wild-type HFE was greatly increased in the presence of transferrin as revealed by cell-attached recordings. According to their calculated diameters, many of these vesicles corresponded to clathrin-coated vesicles. These results suggest that wild-type HFE negatively modulates the endocytic uptake of transferrin. This inhibitory effect is attenuated in cells expressing C282Y-mutant HFE. Time-resolved measurements of cell membrane capacitance provide a powerful tool to study transferrin-induced endocytosis in single cells.