PGE2 is the main prostaglandin produced in bone tissue and is synthesized and secreted by osteoblastic cells. It has proven to act in a biphasic manner having a mitogenic and stimulatory effect on osteoblasts, but also facilitating the differentiation of hematopoietic cells into osteoclasts. Arachidonic acid (AA) is the precursor molecule of PGE2 and eicosanoids in general. Under resting conditions AA is esterified to the phospholipids of cell membranes. In MC3T3-E1 cells AA is known to be released in a Ca2+-dependent manner via the catalytic action of PLA2, mobilization of Ca2+ stores and subsequent sustained Ca2+ entry through store-gated channels. Previous experiments have shown that upon stimulation of MC3T3-E1 cells with ET-1 PGE2 synthesis was active even in the absence of extracellular Ca2+. Moreover, addition of Ni2+, a potent inhibitor of Ca2+ channels, increased PGE2 production significantly. This phenomenon is known as "nickel effect". We tried to elucidate the pathways involved in a Ca2+-independent release of AA, using PCR, Western Blot and enzyme blocking. Special emphasis was put on PLD1 and D2, as an involvement of these enzymes in the Ca2+-independent ET-1 stimulated release of AA was previously reported by O. Kozawa et al.. Also, for the first time, in this thesis direct evidence for the expression of several isoforms of the phospholipase D and A2 superfamily was provided on mRNA and protein level under resting as well as under stimulated conditions.The Ni2+-effect appears to be a feature of untransformed osteoblastic cells and that there are explicit indications of an involvement of phospholipase D1 and D2 in the ET-1 induced production of PGE2. Remarkably, despite having deprived cells of extracellular Ca2+, the bulk of PGE2 production appears to be generated through the Ca2+-dependent pathway of PLA2 activation, while PLD1 und PLD2 activity seems to account for only approximately 25% of prostaglandins produced.