Gap junctions mediate intercellular calcium signalling in cultured articular chondrocytes

Abstract

Gap junction-mediated intercellular communication has been implicated in a variety of cellular functions. Among these, signal transduction can be coordinated among several cells due to gap junctional permeability to intracellular second messengers. Chondrocytes from articular cartilage in primary culture respond to extracellular ATP by rhythmically increasing their cytosolic Ca 2+, concentration. Digital imaging fluorescence microscopy of Fura-2 loaded cells was used to monitor Ca 2+ in confluent and semi-confluent cell layers. Under these conditions, Ca 2+, spikes propagate from cell to cell giving rise to intercellular Ca 2+, waves. The functional expression of gap junctions was assessed, in confluent chondrocyte cultures, by the intercellular transfer of Lucifer yellow dye in scrape-loading experiments. Intercellular dye transfer was blocked by the gap junction inhibitor 18α-glycyrrhetinic acid. In imaging experiments, the inhibitor caused the loss of synchrony of ATP-induced Ca 2+, oscillations, and blocked the intercellular Ca 2+, propagation induced by mechanical stimulation of a single cell in a monolayer. It is concluded that gap junctions mediate intercellular signal transduction in cartilage cells and may provide a mechanism for co-ordinating their metabolic activity.