Role of L- and N-type Ca2+ channels in muscarinic receptor-mediated facilitation of ACh and noradrenaline release in the rat urinary bladder.
1. 3H-Noradrenaline (NA) and 14C-acetylcholine (ACh) released by electrical field stimulation were measured simultaneously in strips from the body of rat urinary bladder. 2. omega-Conotoxin GVIA (omega-CgTX; 20-100 nM) suppressed the non-facilitated transmitter release evoked by intermittent stimulation (IS), whereas nifedipine (1 microM) did not affect release. 3. Continuous electrical stimulation (CS) facilitated NA and ACh release via an atropine-sensitive mechanism. omega-CgTX reduced the facilitated release of NA (44% depression) but did not affect ACh release. Nifedipine depressed ACh release (43%) but not NA release. Combined administration of nifedipine and omega-CgTX (20 nM) produced a greater suppression of NA and ACh release (86 and 91%, respectively). 4. Maximal muscarinic facilitation of NA (5-fold) and ACh (17-fold) release occurred following administration of eserine, an anticholinesterase agent. Release of both NA and ACh was depressed by nifedipine (70 and 83%, respectively) but not by omega-CgTX. Combined application of omega-CgTX and nifedipine elicited a further depression of NA (95%) but not ACh release. 5. When NA and ACh release was facilitated with phorbol dibutyrate (0.5 microM), nifedipine inhibited ACh (67%) but not NA release, whereas omega-CgTX inhibited NA (73%) but not ACh release. Combined administration of both Ca2+ channel blockers did not elicit greater inhibition. 6. Bay K 8644, the L-type Ca2+ channel activator, increased ACh release in a dose-dependent manner (up to 5-fold) but did not significantly change NA release. 7. Both omega-CgTX (20-100 nM) and nifedipine (100 nM-1 microM) significantly decreased (50-80%) the neurally evoked contractions of the bladder strips. 8. It is concluded that L-type Ca2+ channels play a major role in muscarinic facilitation of NA and ACh release in the urinary bladder but are not essential for non-facilitated release. Other types of Ca2+ channels, including N-type, are involved to varying degrees in non-facilitated and facilitated release under different experimental conditions.
Somogyi
G T
GT
Department of Pharmacology, University of Pittsburgh, PA 15261, USA. somo+@pitt.edu
Zernova
G V
GV
Tanowitz
M
M
de Groat
W C
WC
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism*; D020866:omega-Conotoxin GVIA
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D010455:Peptides; D011976:Receptors, Muscarinic; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D020866:omega-Conotoxin GVIA; D009543:Nifedipine; D000109:Acetylcholine; D009638:Norepinephrine