Okadaic acid inhibits relaxant neural transmission in rat gastric fundus in vitro.
The aim of the present study was to characterize the influence of the phosphatase type 1 and 2A inhibitor okadaic acid on non-adrenergic, non-cholinergic (NANC) neurotransmission in the rat gastric fundus. Okadaic acid (10-6 M), an inhibitor of protein phosphatases 1 and 2A, did not show any influence on the basal tonus or on a contraction plateau induced by 5-HT (10-7 M) within 30 min of observation. When okadaic acid (10-6 M) was applied 10 min prior to 5-HT (10-7 M), the contraction plateau of serotonin was unchanged. To investigate the inhibitory neurotransmission, the muscle strips were pre-contracted using 5-HT (10-7 M), and inhibitory stimuli were applied at the contraction plateau, which was stable over 30 min. The inhibitory effects of vasoactive intestinal peptide (VIP), nitric oxide (NO) and electrical field stimulation (EFS, 40 V, 0.5 ms, frequencies ranging from 0.5 to 16 Hz) were examined. When okadaic acid (10-6 M) was applied prior to EFS-induced NANC relaxation, significant attenuation of the inhibitory response was demonstrated (16 Hz: control: -92.4 +/- 1.9%; okadaic acid 10-7 M: -60.7 +/- 6.1%; okadaic acid 10-6 M: -25.3 +/- 3.4%; n=11; P < 0.01). By contrast, neither the concentration-dependent inhibitory actions of VIP (10-11-10-8 M) (VIP 10-8 M: -100%; VIP 10-8 M + okadaic acid 10-6 M: -89.9 +/- 8.3%; n=8; n.s) nor that of diethylamine nitric oxide (DEA-NO) (3 x 10-7-10-4 M) (DEA-NO 10-4 M: -95.3 +/- 8.4%; DEA-NO 10-4 M + okadaic acid 10-7 M: -98.3 +/- 6.3%; DEA-NO 10-4 M + okadaic acid 10-6 M: 96.5 +/- 7.6%; n=9; n.s.) on 5-HT induced contraction were altered by pre-incubation with okadaic acid (10-6 M). This is the first report that supports the concept that protein phosphatases 1 and 2A may contribute to the regulation of rat gastric fundus motility. The protein phosphatase inhibitor okadaic acid significantly reduces electrically induced inhibitory NANC responses, while leaving direct muscular effects of the inhibitory NANC neurotransmitters VIP and NO unaffected - suggesting a neural site of action. The potential roles of protein phosphatases on NANC neurotransmission remain to be clarified in detail, as this might offer a new pathway for modulating smooth-muscle function.
Storr
M
M
GAP, Department of Internal Medicine II, Technical University of Munich, Ismaningerstr. 22, Munich, Germany.
Folmer
R
R
Kurjak
M
M
Schusdziarra
V
V
Allescher
H D
HD
D000818:Animals; D002227:Carbazoles; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005748:Gastric Fundus / Q000294:innervation* / Q000502:physiology; D005765:Gastrointestinal Agents / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology; D009589:Nitrogen Oxides; D019319:Okadaic Acid / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011688:Purinones / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D002227:Carbazoles; D004791:Enzyme Inhibitors; D005765:Gastrointestinal Agents; D006834:Hydrazines; D007211:Indoles; D020030:Nitric Oxide Donors; D009589:Nitrogen Oxides; D010069:Oxadiazoles; D010726:Phosphodiesterase Inhibitors; D011688:Purinones; D011758:Pyrroles; D011810:Quinoxalines; D019319:Okadaic Acid; D019335:Nitroarginine; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; C057416:KT 5720; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D010749:Phosphoprotein Phosphatases; C011145:zaprinast