Functional coupling between nitric oxide synthesis and VIP release within enteric nerve terminals of the rat: involvement of protein kinase G and phosphodiesterase 5.
1. The subcellular mechanisms involved in the effect of nitric oxide (NO) on the release of vasoactive intestinal polypeptide (VIP) were examined in synaptosomes isolated from rat small intestine. 2. VIP release was stimulated by the NO donor SNAP (10(-7)-10(-4) M) in an oxyhaemoglobin-sensitive manner. The presence of the guanylate cyclase inhibitor ODQ (10(-5) M), or inhibition of protein kinase G (PKG) by KT 5823 (3 x 10(-6) M) or Rp-8Br-PET-cGMPS (5 x 10(-7) M), antagonized the SNAP-induced VIP release, suggesting a regulatory role of PKG, confirming previously published data from enteric ganglia. This finding was further supported by the fact that direct PKG activation by the stable cGMP analogue 8-pCPT-cGMP stimulated VIP secretion to the same extent as SNAP. 3. Basal VIP secretion was enhanced in the presence of zaprinast, an inhibitor of cGMP-dependent phosphodiesterase 5 (PDE 5), suggesting a functional role of PDE 5 in NO-cGMP signalling. Supportive evidence for this finding was obtained by demonstration of the presence of PDE 5 using RT-PCR. 4. Stimulation of endogenous NO production by L-arginine was also effective in releasing VIP. The effect was abolished in the presence of KT 5823, but was insensitive to oxyhaemoglobin (10(-3) M), suggesting that an interaction between NO and VIP is likely to occur within the same nerve terminal rather than between terminals. 5. NO synthesis was not affected by VIP (10(-8)-10(-5) M), suggesting that there is no feedback regulation between the NO and the VIP pathways. 6. These findings support the notion that an anatomical and functional interrelationship exists between NO and VIP in enteric nerve terminals and that complex signalling mechanisms involving PKG and PDE 5 contribute to NO-induced VIP release.
Kurjak
M
M
Department of Internal Medicine II, Technical University of Munich, Ismaninger Strasse 22, 81675 Munich, Germany.
Fritsch
R
R
Saur
D
D
Schusdziarra
V
V
Allescher
H D
HD
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000502:physiology; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D000262:Adenylyl Cyclases / Q000502:physiology; D000818:Animals; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D017615:Enteric Nervous System / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000502:physiology; D007421:Intestine, Small / Q000502:physiology; D008297:Male; D009411:Nerve Endings / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000096:biosynthesis*; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D026423:S-Nitroso-N-Acetylpenicillamine; D013574:Synaptosomes / Q000502:physiology; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D020030:Nitric Oxide Donors; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; D026423:S-Nitroso-N-Acetylpenicillamine; D019001:Nitric Oxide Synthase; D017869:Cyclic GMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat; D000262:Adenylyl Cyclases; D006162:Guanylate Cyclase; D010396:Penicillamine