Visualization of Endocannabinoids in the Cell

A still unsolved, although critical, issue in endocannabinoid research is the mechanism by which the lipophilic anandamide (AEA) moves from its site of synthesis, crosses the aqueous milieu, and reaches the different intracellular membrane compartments, where its metabolic and signaling pathways take place. The difficulty of studying intracellular AEA transport and distribution results from the lack of specific probes and techniques to track and visualize this bioactive lipid within the cells. Herein, we describe the use of a biotinylated, non-hydrolyzable derivative of AEA (biotin-AEA, b-AEA) for visualizing the subcellular distribution of this endocannabinoid by means of confocal fluorescence microscopy.

Correlative imaging to resolve molecular structures in individual cells: Substrate validation study for super-resolution infrared microspectroscopy

Light microscopy has been a favorite tool of biological studies for almost a century, recently producing detailed images with exquisite molecular specificity achieving spatial resolution at nanoscale. However, light microscopy is insufficient to provide chemical information as a standalone technique. An increasing amount of evidence demonstrates that optical photothermal infrared microspectroscopy (O-PTIR) is a valuable imaging tool that can extract chemical information to locate molecular structures at submicron resolution. To further investigate the applicability of sub-micron infrared microspectroscopy for biomedical applications, we analyzed the contribution of substrate chemistry to the infrared spectra acquired from individual neurons grown on various imaging substrates. To provide an example of correlative immunofluorescence/O-PTIR imaging, we used immunofluorescence to locate specific organelles for O-PTIR measurement, thus capturing molecular structures at the sub-cellular level directly in cells, which is not possible using traditional infrared microspectroscopy or immunofluorescence microscopy alone.

Medium-retaining Petri dish insert to grow and image cultured cells

BACKGROUND

Microscope chambers that accept glass coverslips with cultured cells are often used to monitor intracellular Ca²⁺ concentration ([Ca²⁺]_i) during cell superfusion. Unfortunately, the experimental maneuvers associated with the coverslip installation in these chambers (medium removal and re-application) trigger unintended [Ca²⁺]_i elevations.

NEW METHOD

To prevent these [Ca²⁺]_i elevations, a Petri dish insert has been constructed. The insert features a superfusion-optimized well to grow cell cultures. After this insert is removed from the Petri dish, the well retains the medium. This feature allows the inserts to be installed in microscope chambers while keeping the cells submerged at all times.

RESULTS

These inserts were used to test the impact of a transient medium removal from the well (an equivalent of a coverslip removal from the medium) on [Ca²⁺]_i in primary murine cortical neurons and astrocytes, and in HEK-293 cells. In all of these models, the medium removal/re-application caused a micromolar [Ca²⁺]_i spike. While in neurons this spike was caused by a Ca²⁺ influx, in astrocytes and HEK-293 cells, it was caused by a Ca²⁺ release from intracellular stores. After the spike, a subpopulation of neurons failed to restore low [Ca²⁺]_i; in 24% of the astrocytes, the spike triggered [Ca²⁺]_i oscillations. However, prior to the spike, [Ca²⁺]_i was low and uniform in all these cells.

COMPARISON WITH EXISTING METHOD(S)

The new method avoids the artificially-induced [Ca²⁺]_i elevations that take place during the handling of glass coverslips with cultured cells.

CONCLUSIONS

The new method allows monitoring [Ca²⁺]_i without disturbing the basal [Ca²⁺]_i levels.