Astrocytes are the most numerous cells in the mammalian brain. Through an intimate relationship with their neuronal neighbours they perform a range of functions including the regulation of synaptic communication. Astrocytes have been implicated in the pathogenesis of numerous diseases including Alzheimer’s disease. In cultures of rat astrocytes, the pathogenic Aβ1-42 peptide is reported to up-regulate the expression of nicotinic receptors (Xiu et al 2005). To investigate this pathway in cells derived from man we have initiated functional studies of the HTB-15 human astrocytoma. This cell-line is reported to express nicotinic α7 receptors in a fashion regulated by both cholesterol and the cholesterol lowering drug lovastatin, agents that also modify the processing of the amyloid precursor protein by these cells (Xiu et al 2006). HTB-15 cells were cultured on glass coverslips in DMEM supplemented with 10% FCS. Cells were loaded with the Ca2+ sensitive dye Fura2 by transferring them to a standard HEPES-buffered saline (HBSS) supplemented with 2 μM Fura2-AM and pluronic F-127 0.02%w/v at 37C. After 30 mins the cells were washed with, and maintained in, HBSS at room temperature for up to 150 min. before being used in experiments. Ratiometric fluorescence imaging was performed on the stage of an inverted microscope in a constantly perfused low-volume chamber. Ratio images proportional to intracellular Ca2+ ([Ca2+]i) were collected every 5 s, using well-established methods. Drugs were applied by addition to the perfusing solution. Under control conditions a proportion of the HTB-15 cells exhibited large and regular Ca2+ oscillations with frequencies between ~0.05 and 0.005 Hz. Removal of extracellular Ca2+ caused a rapid drop in basal [Ca2+]i and eliminated oscillations in some, but not all, cells. Re-addition of extracellular Ca2+ elicited a rebound [Ca2+]i transient that rose considerably above initial baseline levels. Histamine (50 or 100 μM) caused a large and reproducible [Ca2+]i mobilization response in >90% of cells. Cell by cell analysis revealed that histamine-induced Ca2+ oscillations. Histamine responses were eliminated by the H1 antagonist pyrilamine. Both ATP and ADP produced Ca2+ mobilization responses that exhibited profound tachyphalaxis. Muscarinic agonism elicited a pirenzepine-sensitive mobilization response, although this was only seen in around 35 % of cells. Although nicotine (100 μM) produced clear Ca2+ responses these were observed in <15% of cells. These responses were sensitive to 100 nM MLA a selective α7 antagonist. In addition, a large potentiation of nicotine responses was seen in the presence of the α7-specific positive allosteric modulator PNU120956 (1 μM).