The human placenta develops from trophoblasts of the blastocyst and provides an interface of communication and exchange of material between mother and fetus. Trophoblasts are frontline epithelial cells involved in such activities, in which Ca2+-signalling proteins are richly expressed (Moeau et al., 2003). Intracellular free calcium ions ([Ca2+]i) are a key second messenger, participating in regulation of various cellular activities (Berridge et al., 2003). In the placenta, transcellular Ca2+ transport through trophoblasts is essential in formation of the fetal skeleton (Belkacmi et al., 2005). Ryanodine receptors (RyRs) are high conductance cation channels that mediate Ca2+ release from intracellular Ca2+ to the cytoplasm. To date, the presence and physiological roles of RyRs in trophoblasts have not been reported. A pilot study from our laboratory revealed that functional RyRs are expressed in model trophoblast cell lines. In the current study, RNA encoding RyRs was confirmed in human trophoblast cell-lines (BeWo, JAR, JEG-3 and SGHPL-4) using reverse transcription-PCR. The presence of RyR1 and RyR accessory protein, triadin, were demonstrated in BeWo and JEG-3 trophoblastic cells by immunoblotting and indirect immunofluorescence microscopy. Change of [Ca2+]i was monitored by loading the cells with fura-2 acetoxymethyl ester (AM) and by using fluorescent videomicroscopy system. When BeWo cells were exposed to 1 µM ryanodine, an initial 12.7 ± 1.0% (mean ± standard error in mean (SEM), n = 4) increase of mean fura-2 ratio (i.e. increased [Ca2+]i) was observed. When these cells were treated with 500 µM 4-chloro-meta-cresol (CmC), an RyR1 and RyR2 activator, an initial increase in mean fura-2 ratio of 27.3 ± 1.5% (mean ± SEM, n = 6) was detected, followed by a rapid decrease of signal. Alterations in cell morphology detected by using brightfield videomicroscopy were also observed in these cells in response to RyR activators. Cells were loaded with calcein AM (Crowe et al., 1994) to monitor if changes in cell morphology were due to change in cell volume. Addition of 500 µM CmC caused decrease in calcein fluorescence intensity/initial intensity ratio of 11.8 ± 0.6% (mean ± SEM, n = 4) within 6 minutes in BeWo cells, indicating an increase in cell volume following RyR activation. These findings demonstrate that BeWo and JEG-3 express multiple RyR subtypes, along with certain accessory proteins, and that these channel complexes participate in cell volume regulation.