Ca2+, nitric oxide (NO), and protein kinase G (PKG) are important signaling molecules that play pivotal roles in many physiological processes such as vascular tone control, platelet activation, and synaptic plasticity. TRPC channels allow Ca2+ influx, thus contributing to the production of NO, which subsequently stimulates PKG. It has been demonstrated that PKG can phosphorylate human TRPC3 at Thr-11 and Ser-263 and that this phosphorylation inactivates TRPC3. These two PKG phosphorylation sites, Thr-11 and Ser-263 in human TRPC3, are conserved in other members of the TRPC3/6/7 subfamily, suggesting that PKG may also phosphorylate TRPC6 and TRPC7. In addition, protein kinase C (PKC) also inactivates TRPC3, partly through activating PKG. The PKG-mediated inhibition of TRPC channels may provide a feedback control for the fine tuning of [Ca2+]i levels and protect the cells from the detrimental effects of excessive [Ca2+]i and/or NO.