Cytosolic calcium and membrane potential in articular chondrocytes during parabolic flight

Chondrocytes are the sole resident cells in articular cartilage, which line the articulating bones in joints allowing effortless movements. Chondrocytes are responsible for cartilaginous matrix synthesis, maintenance and degradation. Since these cells are frequently exposed to mechanical loading patterns, it is generally believed that chondrocytes require mechanical stimuli for adequate cartilage homeostasis. In this context, mechanosensitive ion channels are thought to be among the first instances in cellular mechanosensing. Prior studies showed that applied mechanical stimuli increase cytosolic free calcium and hyperpolarization of the cells’ membrane potential. We used an adapted commercial plate reader during a parabolic flight to examine whether cytosolic free calcium and membrane potential are gravity-dependent. Our experiments showed that both cytosolic free calcium and membrane potential remain unchanged in response to short periods of increased or reduced gravity. Careful data analysis also revealed some pitfalls and shortcomings when using a commercial plate reader during a parabolic flight.