We recently demonstrated that PC12 cells cultured on extracellular matrix (ECM) exhibit a flattened morphology, release more dopamine and contain less intracellular dopamine than cells which have a rounded shape on plastic culture ware. To further explore the role of PC12 cell shape in dopamine processing, we characterized the interaction of ECM and various agents on cell shape and dopamine release and content. In addition, the constituents of the ECM and the corneal endothelial cells which produce the ECM were presented in soluble form to PC12 cells on plastic. The soluble polysaccharides heparin, dextran and dextran sulfate, caused a dose-related increase in rounded (refractile) cells on ECM, a dose-related decrease in dopamine release and an increase in dopamine content relative to flattened cells on ECM. Chondroitin sulfate and hyaluronic acid did not prevent cell spreading on ECM nor affect dopamine processing. These experiments demonstrate that certain polysaccharides block cell spreading on ECM and that round cells on ECM secrete and store dopamine in a fashion similar to round cells on plastic. Colchicine, cytochalasin B and cycloheximide appear to affect dopamine synthesis and thus could not distinguish the role of cell shape in transmitter release. Treatment of PC12 cells on plastic with collagens I, II, III, IV, fibronectin, fibroblastic growth factor (FGF), or solubilized ECM had little effect on dopamine release or content. Endothelial cell conditioned medium and endothelial cell lysate increased dopamine release, but also increased dopamine content which differs from the effect of ECM. In summary, these experiments suggest that extracellular matrix alters cell shape and that the physical arrangement of these cells can determine dopamine secretion and storage.