Nitric oxide-sensitive guanylyl cyclase is the only nitric oxide receptor mediating platelet inhibition.
BACKGROUND
The nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling cascade is involved in the precise regulation of platelet responses. NO released from the endothelium is known to activate NO-sensitive guanylyl cyclase (NO-GC) in platelets. By the generation of cGMP and subsequent activation of cGMP-dependent protein kinase (PKG), NO-GC mediates the reduction of the intracellular calcium and inhibits platelet adhesion and aggregation. However, NO has been postulated to influence these platelet functions also via cGMP-independent mechanisms.


OBJECTIVE
We studied the effect of NO on platelets lacking NO-sensitive guanylyl cyclase with regards to aggregation, adhesion, calcium mobilization and bleeding time.


RESULTS
Here, we show that NO signaling leading to inhibition of agonist-induced platelet aggregation is totally abrogated in platelets from mice deficient in NO-GC (GCKO). Even at millimolar concentrations none of the several different NO donors inhibited collagen-induced aggregation of GCKO platelets. In addition, NO neither affected adenosine 5'-diphosphate (ADP)-induced adhesion nor thrombin-induced calcium release in GCKO platelets. Although the NO-induced cGMP signal transduction was totally abrogated cyclic adenosine monophosphate (cAMP) signaling was still functional; however, cGMP/cAMP crosstalk was disturbed on the level of phosphodiesterase type 3 (PDE3). These in vitro data are completed by a reduced bleeding time indicating the lack of NO effect in vivo.


CONCLUSIONS
We conclude that NO-GC is the only NO receptor in murine platelets mediating the inhibition of calcium release, adhesion and aggregation: lack of the enzyme leads to disturbance of primary hemostasis.
Institut für Pharmakologie und Toxikologie, Medizinische Fakultät, Ruhr-Universität Bochum, Bochum, Germany.
O
O
Dangel
E
E
Mergia
K
K
Karlisch
D
D
Groneberg
D
D
Koesling
A
A
Friebe
D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology; D006152:Cyclic GMP / Q000378:metabolism; D005089:Exocytosis; D006162:Guanylate Cyclase / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000502:physiology*; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D015398:Signal Transduction; D000071756:Soluble Guanylyl Cyclase
D018160:Receptors, Cytoplasmic and Nuclear; D009569:Nitric Oxide; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D006152:Cyclic GMP