PTH binding to the PTH/PTHrP receptor activates adenylate cyclase (AC) / protein kinase A (PKA) and phospholipase C (PLC) pathways and increases receptor phosphorylation. The mechanisms regulating PTH activation of PLC signaling are poorly understood. In the current study, we explored the role of PTH/PTHrP receptor phosphorylation and PKA in PTH activation of PLC. When treated with PTH, LLCPK-1 cells stably expressing a green fluorescent protein-tagged wild type PTH/PTHrP receptor (WT-GFP) show a small dose-dependent increase in PLC signaling as measured by inositol 1,4,5-trisphosphate (IP3) accumulation assay. In contrast, PTH treatment of LLCPK-1 cells stably expressing a green fluorescent protein-tagged receptor mutated in its carboxyl-terminal tail so that it cannot be phosphorylated (PD-GFP) results in significantly higher PLC activation (p-value < 0.001). The effects of PTH on PLC activation are dose-dependent and reach maximum at the 100 nM PTH dose. When WT receptor-expressing cells are pretreated with H89, a specific inhibitor of PKA, PTH activation of PLC signaling is enhanced in a dose-dependent manner. H89 pretreatment in PD-GFP cells causes a further increase in PLC activation in response to PTH treatment. Interestingly, PTH and forskolin (Adenylate cyclase/PKA pathway activator) treatment causes an increase in PLC3 phosphorylation at the Ser1105 inhibitory site and that increase is blocked by the PKA inhibitor, H89. Expression of a mutant PLC3 in which Ser1105 was mutated to alanine (PLC3-SA), in WT or PD cells increases PTH stimulation of IP3 formation. Altogether, these data suggest that PTH signaling to PLC is negatively regulated by PTH/PTHrP receptor phosphorylation and PKA. Furthermore, phosphorylation at Ser1105 is demonstrated as a regulatory mechanism of PLC3 by PKA.