Extracellular ATP triggers catecholamine secretion from PC12 cells by activating ionotropic purine receptors. Repeated stimulation by ATP leads to habituation of the secretory response. In this paper, we use amperometric detection to monitor the habituation of PC12 cells to mul-tiple stimulations of ATP or its agonist. Cells habituate to 30lMATP slower than they do to 300 or 600lMATP. Modifying external Mg2+ affects the response of cells to 30lMATP, but does not affect habituation, suggesting that habituation does not necessarily correspond to either sti-mulus intensity or cellular response. .
