Energy metabolism, replicative ability, intracellular calcium concentration, and ionic channels of horse articular chondrocytes.

The researchers studied several aspects of horse articular cartilage cell physiology to better understand arthritic processes. They found that these cells have low replication and proteoglycan production capabilities, do not differentiate in culture, and they mainly derive their energy from the glycolytic pathway.

Chondrocyte Replicative Ability and Proteoglycan Production

• The research results showed that horse articular chondrocytes have a very low replicative ability or rate of multiplication in a given time period. This was measured by observing the incorporation of thymidine marked with radioactive tritium ([3H]thymidine).
• Additionally, these cells also possess a low capacity for proteoglycan production, which is crucial to building and maintaining cartilage health. This ability was evaluated using the incorporation of sulfate marked with radioactive sulfur ([35S] sulfate).

Chondrocyte Differentiation

• The study also discovered that these cells do not undergo differentiation in in-vitro cell cultures, which is indicated by the constant specific activity of the enzyme alkaline phosphatase at different times in culture. Differentiation signifies the process by which a less specialized cell becomes a more specialized cell type.

K+ Channels in Chondrocytes

• Through patch clamp experiments, two different types of potassium (K+) channels were identified in these cells. One had a conductance of 40 pS and the other had a conductance of 100 pS. Conductance is a measure of how easily electricity (or in this case, ions) flow through a channel.
• Regardless, no active K+ channels were found when the holding potential (Vpip) equaled 0.

Intracellular Calcium Concentration

• The study also revealed that the low replication capability of the chondrocytes is associated with a small variation in the concentration of calcium within the cells, even after the cells were stimulated mitogenically. This finding came from experiments using Fura-2, a fluorescence-based calcium indicator.

Energy Metabolism in Chondrocytes

• Last, the research indicates that the chondrocytes get the majority of their energy from the glycolytic pathway. This was demonstrated by 31P NMR experiments conducted on slices of whole articular cartilage and on isolated cells. The glycolytic pathway is a type of metabolic pathway that breaks down glucose for energy.