Effects of immunization against VIP on neurotransmission in cat trachea

Multiple calcium channels regulate neurotransmitter release from vagus nerve terminals in the cat bronchiole

1. Twitch-like contractions and non-adrenergic non-cholinergic (NANC) relaxations evoked by electrical field stimulation (EFS) of the cat bronchiole were used to examine the voltage-activated calcium channels involved in excitatory and inhibitory neurotransmission in the cat bronchiole. 2. Nifedipine (50 microM), the L-type calcium channel antagonist, did not affect the twitch-like contraction and NANC relaxations. However, low concentrations of the N-type calcium channel blocker omega-conotoxin GVIA (omega-CgTX GVIA) (0.1 microM) irreversibly abolished twitch-like contractions evoked by trains of EFS </=10 stimuli at 20 Hz. 3. After the prolonged treatment with 0.1 microM omega-CgTX GVIA, EFS evoked initial fast and later slow NANC relaxations in the presence of 5-HT (10 microM), atropine and guanethidine (1 microM each). However increased concentration of omega-CgTX GVIA (1 microM) completely suppressed the slow NANC relaxation without affecting the initial fast component. 4. omega-agatoxin IVA (100 nM), the P- and Q-type calcium channel inhibitor, and nimodipine (10 microM), the L- and T-type calcium channel blocker, did not affect the amplitude of the initial fast NANC relaxation in the absence or presence of omega-CgTX GVIA (1 microM). 5. The contraction or relaxation induced by exogenous acetylcholine (ACh) (0.5 microM) or the nitric oxide donor, s-nitroso-N-acetyl penicillamine (SNAP) (1 microM) were not affected by omega-CgTX GVIA (1 microM). 6. Taken together, these results suggest that generation of twitch-like contraction and later slow NANC relaxation are regulated by N-type calcium channels, whereas generation of the initial fast NANC relaxation possibly involves R-type calcium channel.

Regional difference in the distribution of L-NAME-sensitive and -insensitive NANC relaxations in cat airway

1. To investigate the distribution profile of functional inhibitory non-adrenergic non-cholinergic (i-NANC) nerves and the contribution of NO to the NANC relaxation in the cat, we studied the effects of N omega-nitro-L-arginine methyl ester (L-NAME) on NANC relaxation elicited by electrical field stimulation (EFS) in the trachea, bronchus and bronchiole. 2. EFS applied to the tracheal smooth muscle during contraction induced by 5-HT (10(-5) M) in the presence of atropine (10(-6) M) and guanethidine (10(-6) M) elicited a monophasic NANC relaxation. By contrast, NANC relaxation elicited in the peripheral airway was biphasic, comprising an initial fast followed by a second slow component and L-NAME (10(-5) M) selectively abolished the first component without affecting the second one. In the trachea, L-NAME (10(-5) M) completely suppressed the monophasic NANC relaxation when single or short repetitive stimuli (< 5) with 1 ms pulse duration were applied. However, at higher repetitive stimuli (> 10) with 1 or 4 ms pulse duration, suppression of NANC relaxation was incomplete. 3. In the small bronchi obtained from L-NAME-pretreated cats, EFS applied during contraction induced by 5-HT (10(-5) M) elicited only the slow component of NANC relaxation which is sensitive to tetrodotoxin. 4. In the peripheral airway, a newly synthesized VIP antagonist (10(-6) M) or alpha-chymotrypsin (1 U ml-1) considerably attenuated the amplitude of L-NAME-insensitive relaxation. 5. Single or repetitive EFS consistently evoked excitatory junction potentials (EJPs) in the central and peripheral airways. When tissues were exposed to atropine (10(-6) M) and guanethidine (10(-6) M), single or repetitive EFS did not alter the resting membrane potential. 6. These results indicate that at least two neurotransmitters, possibly NO or NO-containing compounds and VIP, are involved in i-NANC neurotransmission and the distribution profile of the two components differs in the central and peripheral airway of the cat.

Role of nitric oxide in non-adrenergic, non-cholinergic relaxation and modulation of excitatory neuroeffector transmission in the cat airway

1. The effects of nitrosocysteine (cys-NO), L-N omega-nitroarginine (L-NNA) and L-N omega-nitro-L-arginine methylester (L-NAME), oxyhaemoglobin and Methylene Blue were observed on the resting membrane potential, muscle tone and excitatory junction potentials (EJPs) of cat tracheal smooth muscle tissue. 2. Cys-NO (10(-9) to 10(-6) M) showed no effect on the resting membrane potential of smooth muscle cells of the cat trachea but it dose-dependently relaxed the tracheal tissue in the presence of 5-HT, atropine and guanethidine. 3. Electrical field stimulation (EFS) applied during contraction evoked by 5-HT in the presence of atropine and guanethidine evoked non-adrenergic, non-cholinergic (NANC) muscle relaxation. L-NNA (10(-4) M) and L-NAME (10(-4) M) completely suppressed the relaxation when single or short repetitive stimuli were applied, but suppression was incomplete with repetitive stimuli of 4 ms pulse duration applied at 20 Hz. A substantial part of the L-NNA- or L-NAME-insensitive relaxation was abolished by tetrodotoxin. 4. Cys-NO dose-dependently suppressed the EJPs without changing the resting membrane potential, and L-NNA, L-NAME, Methylene Blue and oxyhaemoglobin enhanced the amplitude of the EJP to 1.2-1.5 times the control value. 5. EJPs showed some summation when repetitive field stimulation was applied at 20 Hz. L-NNA or L-NAME enhanced the summation, and the mean slopes were increased from 0.61 +/- 0.22 to 2.0 +/- 0.3, or 1.9 +/- 0.2 mV per stimulus. Vasoactive intestinal polypeptide (VIP) antiserum and VIP antagonists further enhanced the summation in the presence of L-NNA. 6. These results indicate that NANC relaxation can be classified into two different components according to the threshold for activation, and nitric oxide is involved in one. The present results also suggest that endogenous or exogenous nitric oxide has a prejunctional action in inhibiting excitatory neuroeffector transmission in addition to a direct action on the smooth muscle cells, presumably by suppressing transmitter release from the vagus nerve.

Catalytic activity of anti-ground state antibodies, antibody subunits, and human autoantibodies

Catalytic antibodies may be produced over the natural course of antibody-affinity maturation by placement of chemically reactive residues in antibody-active sites by somatic hypermutation or V-D-J-gene rearrangement. This hypothesis has received support from recent observations on the chemical reactivity of antibodies to vasoactive intestinal peptide (VIP), DNA, and steroid- and dinitrophenyl-esters. Recent studies reveal that monoclonal antibodies raised against the ground state of VIP can accelerate the cleavage of peptide bonds. The light-chain (L-chain) subunit of human autoantibodies display increased hydrolytic rate and diminished VIP-binding affinity compared to the parent antibody, consistent with increased turnover owing to weaker binding of the substrate ground state. These observations reveal an essential limitation of catalytic antibodies, i.e., large turnover rates may be associated with diminished substrate specificity. The hydrolysis of VIP by IgG purified by affinity chromatography from asthma patients and nonasthmatic controls was compared. IgG from the majority of asthma patients displayed VIP-hydrolyzing activity. Vmax values for IgG from asthmatics tended to be higher than those from the nonasthmatic group. In principle, catalysis by antibodies may be an important mediator of immunological defense, regulation, and autoimmune dysfunction. The verification of these possibilities will require studies that utilize efficient assays of antibody catalysis during experimental immunization and autoimmune disease, as well as mechanistic investigation of catalysis by antibodies and their subunits.

Colocalization of vasoactive intestinal peptide and nitric oxide synthase in neurons of the ferret trachea

Neurally-mediated relaxation of smooth muscle in human, guinea-pig, cat, and pig airways is largely attributed to a nonadrenergic, noncholinergic mechanism. While the specific transmitter(s) of this relaxant system have not been conclusively identified, vasoactive intestinal peptide and nitric oxide have emerged as likely mediators in airway smooth muscle. Both vasoactive intestinal peptide and nitric oxide relax guinea-pig, pig and human smooth muscle. Vasoactive intestinal peptide is present in nerve fibers associated with airway smooth muscle in humans and several animal species. In guinea-pigs, vasoactive intestinal peptide is released during electrical field stimulation of airway strips and the release correlates with the nonadrenergic relaxation. This relaxation is markedly reduced after incubation of tracheal tissue with a specific VIP antibody and by immunization to vasoactive intestinal peptide. Similarly, nonadrenergic relaxations induced by electrical field stimulation are reduced in human, pig, guinea-pig and bovine airways by nitric oxide synthesis inhibitors. Vasoactive intestinal peptide is present in nerve cell bodies of airway ganglia, suggesting that these nerves in airway smooth muscle originate from intrinsic neurons. It is stored in dense-core vesicles of nerve terminals near airway smooth muscle, suggesting that preformed vasoactive intestinal peptide is released by fusion of the vesicles with the cell membrane of the nerve terminal. Nitric oxide is probably generated by a novel mechanism involving de novo synthesis at the nerve terminal during neural activation by the action of the enzyme nitric oxide synthase.(ABSTRACT TRUNCATED AT 250 WORDS)