Alpha-latrotoxin-induced transmitter release in feline oesophageal smooth muscle: focus on nitric oxide and vasoactive intestinal peptide.
1. The effects of alpha-latrotoxin (alpha LTX) on muscle tone, resting membrane potential, cyclic nucleotide content, and ultrastructure were examined in feline oesophageal smooth muscle, including the lower oesophageal sphincter (LOS). 2. In circular smooth muscle strips from LOS developing active tone alpha LTX (1 nM) induced a 94 +/- 3% (n = 16) relaxation. Intermittent treatment with alpha LTX for 4 h abolished the response. Pretreatment with NG-nitro-L-arginine (L-NOARG; 0.1 mM) attenuated the relaxation. 3. In carbachol-contracted circular smooth muscle strips from the LOS and oesophageal body (OB), alpha LTX induced a 95 +/- 5% (n = 6) and 73 +/- 9% (n = 8) relaxation, respectively. The relaxations were attenuated by L-NOARG, and in LOS strips, the relaxation was abolished by the combination of L-NOARG and vasoactive intestinal peptide (VIP)-antiserum (1:25). At resting tension in circular smooth muscle strips from the OB, alpha LTX induced a scopolamine sensitive contraction in the presence of L-NOARG. 4. In circular LOS and OB preparations, alpha LTX changed the resting membrane potential from -49 +/- 2mV to -59 +/- 3 mV (n = 4), and -62 +/- 2 mV to -71 +/- 3 mV (n = 4), respectively. 5. The alpha LTX-induced relaxation of LOS and OB muscle was associated with a 138% and 72% increase in cyclic GMP levels, respectively. No changes in cyclic AMP levels were observed. 6. Ultrastructural analysis of LOS and OB revealed a rich supply of nerve profiles containing small synaptic and large dense core vesicles. alpha LTX treatment resulted in a loss of both types of vesicle. 7. These results suggest that alpha LTX induces relaxation of oesophageal circular smooth muscle associated with NO-generation and transmitter release from synaptic vesicles. Beside NO, VIP seems to be involved in the relaxant effects of alpha LTX on the LOS. In addition, alpha LTX may have contractile effects by release of acetylcholine.
Ny
L
L
Department of Clinical Pharmacology, Lund University Hospital, Sweden.
Waldeck
K
K
Carlemalm
E
E
Andersson
K E
KE
D000818:Animals; D002415:Cats; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004947:Esophagus / Q000294:innervation / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000294:innervation* / Q000378:metabolism / Q000648:ultrastructure; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D004791:Enzyme Inhibitors; D018377:Neurotransmitter Agents; D013111:Spider Venoms; D019335:Nitroarginine; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; C020763:alpha-latrotoxin; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP