Phosphodiesterase type 2 and the homeostasis of cyclic GMP in living thalamic neurons

Abstract

The ubiquitous second messenger cyclic GMP (cGMP) is synthesized by soluble guanylate cyclases in response to nitric oxide (NO) and degraded by phosphodiesterases (PDE). We studied the homeostasis of cGMP in living thalamic neurons by using the genetically encoded fluorescence resonance energy transfer sensor Cygnet, expressed in brain slices through viral gene transfer. Natriuretic peptides had no effect on cGMP. Basal cGMP levels decreased upon inhibition of NO synthases or soluble guanylate cyclases and increased when PDEs were inhibited. Single cell RT-PCR analysis showed that thalamic neurons express PDE1, PDE2, PDE9, and PDE10. Basal cGMP levels were increased by the PDE2 inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and BAY60-7550 but were unaffected by PDE1 or PDE10 inhibitors. We conclude that PDE2 regulates the basal cGMP concentration in thalamic neurons. In addition, in the presence of 3-isobutyl-1-methylxanthine (IBMX), cGMP still decreased after application of a NO donor. Probenecid, a blocker of cGMP transporters, had no effect on this decrease, leaving PDE9 as a possible candidate for decreasing cGMP concentration. Basal cGMP level is poised at an intermediate level from which it can be up or down-regulated according to the cyclase and PDE activities.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

“…PDE2 is involved in aldosterone production (226), control of cGMP level in certain neurons (143), learning and enhancement of neuronal plasticity (309,331,386), modulation of cardiac L-type calcium current (104), control of specific cGMP pools in cardiomyocytes (58), blunting of anxiety (235), and impacting endothelial cell permeability (338,366). Inhibition of PDE2 in any of these cells could result in elevation of cGMP, cAMP, or both cNs, thereby impacting both cAMP and cGMP signaling.…”

Immunohistochemical assessment of cyclic guanosine monophosphate (cGMP) and soluble guanylate cyclase (sGC) within the rostral ventrolateral medulla

“…This may be the mechanism by which functional differences in the SHR and WKY are delineated and future studies investigating this possibility are warranted. Basal cGMP levels in neurons are the result of a dynamic equilibrium between synthesis, driven by NOsGC, and the rate of degradation by PDEs, [61]. The rate of synthesis can change with time due to desensitisation of sGC, and cGMP kinetics can vary between not only different cell types but also different regions of the brain [62].…”

Real-time monitoring of cyclic nucleotide signaling in neurons using genetically encoded FRET probes

“…This level was not further increased by blockers of phosphodiesterases, thus representing R max . Guanylyl cyclase could be rapidly and efficiently blocked by 10 µM ODQ which, together with the strong endogenous phosphodiesterase activity, rapidly led to a ratio level significantly lower than baseline (Hepp et al, 2007). This level can be reasonably assumed to be close to R min .…”

“…The CGY sensor has been further modified by fusing it to guanylyl cyclase, thus creating a probe sensitive to low NO concentrations (Sato et al, 2005). This may be useful in neuronal preparations to detect very low NO (Hepp et al, 2007).…”

“…Quantification could be pushed a bit further with the cGMP-sensitive probe Cygnet-2 thanks to better pharmacological tools (Hepp et al, 2007). Increasing doses of a NO donor produced increasing ratio responses up to a maximal value for 50 µM DEANO or 100 µM SNAP.…”