Role of anti-calcium channel and anti-receptor autoantibodies in autonomic dysfunction in Sjogren's syndrome

Auto-antibodies cross-reacting with L-type voltage-gated calcium channels (VGCCs) have been described in primary Sjögren's syndrome (pSS), and may mediate the cardiac defects in neonates born to mothers with pSS. L-type VGCCs are also present in autonomically innervated tissues. Therefore, the aim of this project was to investigate a role for anti-VGCC antibodies and antibodies to 1-adrenoceptors or P2X-purinoceptors in the autonomic dysfunction that occurs in pSS. Contraction of the sympathetically innervated vas deferens in response to stimulation of the muscle by an 1-adrenoceptor agonist (phenylephrine) or a P2X-purinoceptor agonist (,β-methylene ATP) was measured in the absence and presence of 2% serum. Contractions produced by phenylephrine and by ,β-methylene ATP were abolished by nicardipine, demonstrating that they are coupled to calcium influx through L-type VGCCs. Serum from patients with pSS or from healthy controls did not significantly alter the L-type channel-dependent responses of smooth muscle to agonist stimulation. We therefore conclude that pSS serum does not contain autoantibodies that functionally inhibit L-type VGCCs, 1-adrenoceptors or P2X-purinoceptors in smooth muscle and that such autoantibodies cannot explain the autonomic dysfunction in pSS.Maria Ohlsson, Tom P. Gordon and Sally A. Waterma

Role of N-, P- and Q-type voltage-gated calcium channels in transmitter release from sympathetic neurones in the mouse isolated vas deferens

1. N-type voltage-gated calcium channels are known to play an important role in transmitter release from autonomic neurones, and recent studies have demonstrated that non-N-type calcium channels are also involved. The calcium channels coupled to transmitter release from sympathetic neurones in the mouse isolated vas deferens were investigated in the present study. 2. Contractions of the mouse vas deferens were evoked by electrical stimulation at 1–50 Hz. The contractions were entirely nerve-mediated, since they were abolished by tetrodotoxin, and were used as an indirect measure of transmitter release. 3. The N-type calcium channel blocker, ω-conotoxin GVIA, inhibited contractions in a concentration-dependent manner, with a maximal effect at 30 nM. Contractions evoked by stimulation frequencies less than 10 Hz were abolished, and those evoked by 20 and by 50 Hz stimulation were decreased in amplitude by 51.3±13.9% and 9.3±2.6%, respectively. 4. The N-, P- and Q-type channel blocker, ω-conotoxin MVIIC, inhibited contractions in a concentration-dependent manner and caused greater maximum inhibition than ω-conotoxin GVIA, suggesting an action on P- and/or Q-type channels, in addition to N-type. 5. The P-type channel blocker, ω-agatoxin IVA, alone did not have a significant effect at concentrations up to 300 nM, but inhibited contractions in the presence of ω-conotoxin GVIA. Subsequent addition of ω-conotoxin MVIIC abolished the remaining contractions. Identical results were obtained when the three toxins were tested cumulatively on the purinergic and noradrenergic components of the contraction in the presence of 0.3 μM prazosin and following desensitization to 10 μM α,β-methylene adenosine 5′-triphosphate (α,β-MeATP), respectively. 6. The results suggest that N-, P- and Q-type channels are involved in the release of noradrenaline and ATP from sympathetic neurones in the mouse vas deferens

Disruption of intestinal motility by a calcium channel-stimulating autoantibody in type 1 diabetes

INDEPENDENCE SQUARE WEST CURTIS CENTER, STE 300, PHILADELPHIA, USA, PA, 19106-339

Neural mechanisms underlying migrating motor complex formation in mouse isolated colon

1. Little is known about the intrinsic enteric reflex pathways associated with migrating motor complex (MMC) formation. Acetylcholine (ACh) mediates the rapid component of the MMC, however a non-cholinergic component also exists. The present study investigated the possible role of endogenous tachykinins (TKs) in the formation of colonic MMCs and the relative roles of excitatory and inhibitory pathways. 2. MMCs were recorded from the circular muscle at four sites (proximal, proximal-mid, mid-distal and distal) along the mouse colon using force transducers. 3. The tachykinin (NK(1) and NK(2)) receptor antagonists SR-140 333 (250 nM) and SR-48 968 (250 nM) reduced the amplitude of MMCs at all recording sites, preferentially abolishing the long duration contraction. Residual MMCs were abolished by the subsequent addition of atropine (1 μM). 4. The neuronal nitric oxide synthase inhibitor, N(ω)nitro-L-arginine (L-NOARG, 100 μM), increased MMC amplitude in the distal region, whilst reducing the amplitude in the proximal region. In preparations where MMCs did not migrate to the distal colon, addition of L-NOARG resulted in the formation of MMCs. Subsequent addition of apamin (250 nM) or suramin (100 μM) further increased MMC amplitude in the distal region, whilst suramin increased MMC amplitude in the mid-distal region. Apamin but not suramin reduced MMC amplitude in the proximal region. Subsequent addition of SR-140 333 and SR-48 968 reduced MMC amplitude at all sites. Residual MMCs were abolished by atropine (1 μM). 5. In conclusion, TKs, ACh, nitric oxide (NO) and ATP are involved in the neural mechanisms underlying the formation of MMCs in the mouse colon. Tachykinins mediate the long duration component of the MMC via NK(1) and NK(2) receptors. Inhibitory pathways may be involved in determining whether MMCs are formed