Inhibition of “spontaneous,” notochord‐induced, and collagen‐induced in vitro somite chondrogenesis by the calcium ionophore, A23187

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Abstract
The present study represents a first step in investigating the possible involvement of calcium (Ca2+) in the stimulation of somite chondrogenesis elicited by extracellular matrix components produced by the embryonic notochord. The ionophore, A23187, a drug that facilitates Ca2+ uptake leading to elevation of cytoplasmic Ca2+ levels, at concentrations of 0.25–1.0 ug/ml severely impairs “spontaneous” somite chondrogenesis, i.e., inhibits the formation of the small amount of cartilaginous matrix normally formed by embryonic somites in vitro in the absence of inducing tissues. This inhibition is reflected in a considerable reduction in sulfated glycosaminoglycan (GAG) accumulation by A23187‐treated somite explants. Furthermore, A23187 inhibits the striking stimulation of cartilaginous matrix formation and sulfated GAG accumulation normally elicited by the embryonic notochord and collagen substrates. In fact, 1.0 μg/ml of A23187 reduces sulfated GAG accumulation by somites cultured in association with notochord or on collagen to a level even below that accumulated by somites cultured in the absence of these inductive agents. Although these results must be interpreted with caution, they provide incentive for considering a possible regulatory role for Ca2+ in the chondrogenic response of somites to extracellular matrix components produced by the embryonic notochord.