Berlin 2015 – scientific programme

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BP: Fachverband Biologische Physik

BP 24: Posters: Membranes and vesicles

BP 24.6: Poster

Tuesday, March 17, 2015, 14:00–16:00, Poster A

Exocytotic activity of living cells imaged with surface plasmon resonance microscopy — Stephan Michael, •Matthias Gerhardt, and Carsten Beta — Institut für Physik und Astronomie, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany

Surface plasmon resonance microscopy allows for imaging of the complex refractive index at gold-liquid interfaces. The complex refractive index of the interface mainly depends on the molecular composition of the samples attached to the gold surface regarding its charge and density. In our case Dictyostelium cells were sedimented onto a gold surface to study the cell-substrate interface. In the region of cell-surface attachment, we observed transient localized events characterized by a step-like change in the complex refractive index at the gold-liquid/cell interface. The duration of such events was found to be within 1-2 sec. In the surface plasmon resonance image, those events mostly appeared as disc-shaped objects with a diameter of about 1-2 um within the region of the cell-substrate interface. While sedimented cells displayed such events spontaneously but rarely, a hypoosmotic shock was found to trigger a significantly higher rate of events. Dictyostelium cells equilibrate their osmolarity by releasing dispensable ions into the extracellular space using their contractile vacuole. Since the area of the observed disc-shaped events was found to be within the size of intracellular vesicles (which have been observed in the same cells using bright field microscopy) we conclude that exocytotic activity of the contractile vacuole can be observed by surface plasmon resonance microscopy.