Mechanically induced calcium waves in articular chondrocytes are inhibitedby gadolinium and amiloride

Chondrocytes in articular cartilage utilize mechanical signals from their e nvironment to regulate their metabolic activity. However, the sequence of e vents involved in the transduction of mechanical signals to a biochemical s ignal is not fully understood. It has been proposed that an increase in the concentration of intracellular calcium ion ([Ca2+](i)) is one of the earli est events in the process of cellular mechanical signal transduction. With use of fluorescent confocal microscopy, [Ca2+](i) was monitored in isolated articular chondrocytes subjected to controlled deformation with the edge o f a glass micropipette. Mechanical stimulation resulted in an immediate and transient increase in [Ca2+](i). The initiation of Ca2+ waves was abolishe d by removing Ca2+ from the extracellular media and was significantly inhib ited by the presence of gadolinium ion (10 mu M) or amiloride (1 mM), which have previously been reported to block mechanosensitive ion channels. Inhi bitors of intracellular Ca2+ release (dantrolene and 8-diethylaminooctyl 3, 4,5-trimethoxybenzoate hydrochloride) or cytoskeletal disrupting agents (cy tochalasin D and colchicine) had no significant effect on the characteristi cs of the Ca2+ waves. These findings suggest that a possible mechanism of C a2+ mobilization in this case is a self-reinforcing influx of Ca2+ from the extracellular media: initiated by a Ca2+-permeable mechanosensitive ion ch annel. Our results indicate that a transient increase in intracellular Ca2 concentration may be one of the earliest events involved in the response o f chondrocytes to mechanical stress and support the hypothesis that deforma tion-induced Ca2+ waves are initiated through mechanosensitive ion channels .