Regulation of intra-Golgi membrane transport by calcium

Calcium cations play a critical role in regulating vesicular transport betw een different intracellular membrane-bound compartments. The role of calciu m in transport between the Golgi cisternae, however, remains unclear. Using a well characterized cell-free intra-Golgi transport assay, we now show th at changes in free Ca2+ concentration in the physiological range regulate t his transport process. The calcium-chelating agent 1,2-bis(2-aminophenoxy)e thane-N,N,N,N'-tetraacetic acid blocked transport with an IC50 of approxima tely 0.8 mM. The effect of 1,2-bis(2- aminophenoxy)ethane-N,N,N',N'-tetraac etic acid was reversible by addition of fresh cytosol and was irreversible when performed in the presence of a Ca2+ ionophore that depletes calcium fr om lumenal stores, We demonstrate here that intra-Golgi transport is stimul ated by low Ca2+ concentrations (20-100 nM) but is inhibited by higher conc entrations (above 100 nM). Further, we show that calmodulin antagonists spe cifically block intra-Golgi transport, implying a role for calmodulin in me diating the effect of calcium. Our results suggest that Ca2+ efflux from in tracellular pools may play an essential role in regulating intra-Golgi tran sport.