High temperature induces the synthesis of heat-shock proteins and the elevation of intracellular calcium in the coral Acropora grandis

Elevated temperatures induce coral bleaching. To investigate subcellular changes in heat-stressed corals, we examined heat-shock proteins (hsps) and the concentration of calcium in coral cells at elevated temperatures. After heat treatment, three hsps with approximate molecular weights of 70, 60 and 35 kDa were prominent. The 35 kDa heat-shock protein was further demonstrated to be heme oxygenase by immunoblotting, suggesting the involvement of oxidative stress in coral cells during heat treatment. Since the expression of hsps needs the activation of a calcium signal, the change of intracellular calcium concentration in coral cells was examined by a FURA 2 fluorescence method under heat treatment. Intracellular calcium concentration increased at high temperatures with or without the presence of ambient calcium. The extent of the calcium concentration increase was constant for at least 6 hours. This result indicates the existence of an active calcium signal in coral cells at elevated temperatures.