PMT has been shown to mediate activation followed by inhibition of the phopholipase C coupled G-proteins Gq (not G11), G12 and G13 (Orth et al, 2005). This study investigated PMTs effects on the resting [Ca]i, P2Y₂R and M1 mAChR mobilisation of [Ca]i in NG108-15 cells. Differentiated cells were loaded with Indo-1 AM (5 μM, 1 h), the dye was excited at 360 nm and emission wavelengths recorded at 405 and 488 nm by photomultiplier tubes (Robbins et al, 1992), calibration was performed as detail earlier (Hayat et al, 2003). P2Y₂R mediate calcium increases were evoked by applying uridine triphosphate (UTP, 1-100 μM) in the presence of CdCl₂ (100 μM) to block voltage gated calcium entry. The concentration-dependence (10-500 ng ml^-1 for 18-24 h) of PMT was complex. A significant increase in resting [Ca]i was seen at 100 and 500 ng ml^-1 PMT, however the amplification of the UTP evoked responses required 500 ng ml^-1. PMT (500 ng ml^-1) was time dependent in its actions. The first effect (3-4 h) was a significant increase in resting [Ca]i from 158 ± 6 nM to 315 ± 22 nM, (n=5). Followed (12-18 h) by an amplification of the UTP evoked [Ca]i increase from 365 ± 8 nM to 1504 ± 37 nM (n=5). Finally (42-48 h) a complete block of UTP mediated responses. The EC₅₀ of the UTP concentration response curve was not significantly altered at any time point. As the change in resting [Ca]i preceded the amplification of the UTP responses, both in terms of concentration and time, we investigated whether the increase in resting [Ca]i was responsible for the amplification of the UTP evoke responses. Resting [Ca]i was significantly lower in cells preincubated in BAPTA-AM (250 μM, 30 min). The resting [Ca]i was reduced in control cells from 158 ± 6 nM to 45 ± 5 nM (n=5) similarly in PMT treated cells the resting [Ca]i decreased from 316 ± 21 to 39 ± 10 nM (n=5). UTP responses were much reduced in the BAPTA-AM treated cells however the amplification of the calcium signal in the PMT treated cells was still evident. In NG108-15 cells transformed to express M1 mAChRs (Robbins et al, 1993) PMT amplified oxotremorine-M (0.1-10 μM) evoked [Ca]i signals without significantly altering the EC₅₀, similar to that seen for P2Y₂ receptors. This amplification was not seen when cells were pretreated with the PMT^(C1165S) mutant which has lost its toxicity and mitogenicity (Baldwin et al, 2003). These results suggest that P2Y₂ and M1 mACh receptors in NG108-15 cells mediate PI turnover and intracellular calcium release by coupling to Gq rather than G11. PMT increases the efficacy of the signalling pathway without a change in the affinity not requiring an increase in the resting [Ca]i.