Affiliations: Department of Orthopaedics, University Hospital, University of Freiburg, Hugstetter Strasse 55, 79106 Freiburg, Germany | Musculoskeletal Research Laboratory, Departments of Orthopaedics and Rehabilitation and Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr, Hershey, PA 17033, USA
Note: [] Address for correspondence: Maximilian Edlich, Department of Orthopaedics, University Hospital, University of Freiburg, Hugstetter Strasse 55, 79106 Freiburg, Germany. Tel.: +49 717 531 4819; Fax: +49 717 531 7583; E‐mail: edlich@ uni‐freiburg.de.
Abstract: Many studies have shown that a loading‐induced (bio)physical signal regulates chondrocyte behavior. In a recent study our group has demonstrated the shear stress level‐ and frequency‐dependent effect of sinusoidal oscillatory fluid flow on bovine articular chondrocyte (BAC) cytosolic calcium concentration ([Ca2+]i), neglecting the fact that chondrocytes are not likely to see these ideal waveform in vivo or in vitro. Furthermore, possible overload of articular cartilage or excessive shear stress in chondrocyte cultures are more likely to be of a short nature. Therefore, in this study we choose to investigate a saw‐tooth waveform oscillating fluid flow at varying exposure times in comparison to the established sinusoidal oscillatory waveform. [Ca2+]i, as an early signaling molecule, was quantified using the fluorescent dye fura‐2. BAC were exposed to 1 Hz sinusoidal or saw‐tooth waveform oscillating fluid flow at 2.2 Pa flow rates in a parallel plate flow chamber for 8 different loading times. As little as 5 cycles of oscillatory fluid flow were sufficient to increase [Ca2+]i significantly over baseline. The number of responding cells could not be increased any further after a sufficient number of cycles (11), regardless of the waveform. Furthermore, a saw‐tooth waveform appeared to be more stimulatory than regular sinusoidal oscillating flow at higher cycle numbers. BAC appear to be able to respond to these biophysical stimuli in a differentiated manner. This ability might give every single chondrocyte the capability to maintain its territory autonomously, since chondrocytes distributed in articular cartilage without the possibility to interact, e.g., via cell processes.
Keywords: Chondrocytes, in vitro, mechanotransduction, fluid flow, shear stress, calcium
Journal: Biorheology, vol. 41, no. 3-4, pp. 315-322, 2004
