Enhancement by calcitonin gene-related peptide of nicotinic receptor-operated noncontractile Ca2+ mobilization at the mouse neuromuscular junction.
1. The involvement of calcitonin gene-related peptide (CGRP) in the mechanism of nicotinic acetylcholine receptor-operated noncontractile Ca2+ mobilization (not accompanied by twitch tension) was investigated by measuring Ca(2+)-aequorin luminescence at the neuromuscular junction of mouse diaphragm muscle treated with neostigmine. 2. Noncontractile Ca2+ transients were enhanced by 4-aminopyridine (100 microM), a K+ channel blocker, and inhibited by botulinum toxin (1-100 micrograms, i.p.) and hexamethonium (10-100 microM), a neuronal nicotinic receptor antagonist. 3. Noncontractile Ca2+ transients were diminished by CGRP8-37 (10-20 microM), a CGRP antagonist. CGRP (0.3-10 nM) prolonged the duration of noncontractile Ca2+ transients. The effect of CGRP was suppressed by CGRP8-37 (0.1 microM). 4. Noncontractile Ca2+ transients were inhibited by H-89 (0.1-1 microM), a protein kinase-A inhibitor. The catalytic subunit of protein kinase-A and AA373 (300 microM), a protein kinase-A activator, prolonged the duration of noncontractile transients. The prolongations either by CGRP or by AA373 were not observed in the presence of H-89 (0.1 microM). 5. Contractile (accompanied by twitch tension) but not noncontractile Ca2+ transients were decreased by 12-O-tetradecanoyl phorbol 13-acetate (TPA, 0.3-1 microM), a protein kinase-C activator. Phospholipase A2 increased only contractile Ca2+ transients. Calmodulin-related agents affected neither type of Ca2+ transients. 6. These results provide the first evidence that nicotinic acetylcholine receptor-operated noncontractile Ca2+ mobilization is promoted by nerve-released CGRP activating protein kinase-A, and is dependent on the accumulated amounts of acetylcholine at the neuromuscular junction where desensitization might readily develop.
Kimura
I
I
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
Tsuneki
H
H
Dezaki
K
K
Kimura
M
M
D000109:Acetylcholine / Q000502:physiology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism*; D010741:Phospholipases A / Q000494:pharmacology; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects*; D017661:Receptors, Presynaptic / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects
D002147:Calmodulin; D011978:Receptors, Nicotinic; D017661:Receptors, Presynaptic; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D015740:Calcitonin Gene-Related Peptide; D000109:Acetylcholine; D002118:Calcium