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Nitric oxide is involved in muscle relaxation but not in changes in short circuit current to electrical field stimulation in rat ileum
1392
ABSTRACTS OF PAPERS
COORJXNATION BETWEEN AND SYMPATHETIC CONTROL CONTRACTION AND ~$~LD~~CU)NIC
October 1992
NlXRICowlBIs -mSDRT -lNmItam Y.F. ti, N.W.
ll!KmJmIN~-KrrmIN ~almmrlm
Vlddmdt, Rrysiology. university a, TX 71030 Bperiments~ oxide @Way(s)
ELIPQRTCUFZEU)
F.G. m. Depts. of Surseryand of Texas Medical school at Ha&on.
designedto &kiy L--inine-nitric activities of intestinal in regulatw
ard m rmSdle in the rat ilamp. An Ussing modified (AmJ Rysiol 261:G166, 1991) so that astxaingage mcarldbeatta&zd lcqi~ly epithelium
chanker
rabbits and a serosal str.& iauge attached to measure CM contractions. Thepreip~y - -was play in an. orgy bath ;d r luminall perfused ~1 Krebs’ solutionat4mllmin Onea axsalt bridge e e&ode was laced m the bathing medmm and anot er inserted into a lumin outflow “T” iece onto which was tied the distal end of the colon. PD was measure4!between these electrodes. The
was
cmtbeeercealstiofilealsegments. m-three nwrkxd ae flat&e&a andvoltage cl@ at potential (FD) . Rzlaxation of the lorq’tudinal rmscle, previarsly mntracted by cd&z&o1 (10Jl4) , an3 &anqea in short circuit azrent (AI,,) in respcplse to B field etinulation (TFS) (5-secarrltrairrs of inpulses, 0.4 IRsinpllse durati No-nitro-Iraryinine @-ML) repeated. Tben,afterwashingan3addingL~3~~inine(LAF~S),TFSwaerepeatedagain. BothAI,,andnueclerelaxation m &own to be freqency dep~&&~ with max3nal VTtedata frequencyof 1OHz. Also, tetxdotaxin (5x10 ) blocked nuscle relaxation and m AI,, by 94% during TFS at 1OHz.
Maximal&lax OXINIL
spontaneous activity in a f uency-dependent manner. At the maximal stimulus strength ?+ e ects on tone were 71+ 19% (LM) and 71f 1396 (CM) (n =6) of the NE maximum. Activity returned to restin levels 11l* 11s (LM) and 47+24s (CM) after the termination of LCN!!. No consistent change in basal PD was observed with LCNS. but oscillations diminished wh& spontaneous muscle activity was abolished. CONCLUSIONS: 1. S ntaneous oscillations in PD and contractile activity occur concurren tp” y and this model may be useful in further investigatmg this phenomenon. 2. LCNS had a strong inhibitorv influence on contractile activitv. 3. The effects of NE and LCNS oii PD were mixed and their role in the control of colonic ion transport remains unclear. Supportedin partby Bgrantfrom the Cmh’s &
2624 I?4 ?? 26+4 E (5xlO.k) 62_+8* L-AX (5xlo‘sM) lOlk9 ** * significant differexe frcelall other grcap (pcO.05) ** significant differexe fmnallgzrap3exceptthe -1 (pCO.05) L+lNJ~blozkedthenuecle relaxation in3ucedbyTFS but
mediatingncnadrenergic,~linergicrelaxaticmMnot mediat~~inello*circuitaurent. (supportedby NIH resea&l grants GM38529, Ex38888)
Colitis Foundation of America.
ACUTE DESENSITIZATIONOF INTESTINALMOTILITY RESPONSE. H.C. Lin, Y.-G. Gu, J.H. Meyer. Depts. of Medicine, Cedars-Sinai Medical Center, Sepulveda VA Medical Center, UCLA, Los Angeles, CA. Acceleration of gastric emptying and omcecal transit were observed following prolonged exposure (14 days) to a high fat diet (Gut 1991;32:483). This effect was postulated to be the result of desensitization of the control mechanism for the motility of the gut. Since mucosal proliferation and enhanced proximal fat absorption may occur following protracted exposure to higher nutrient loads, such a change may result not from desensitization but from the triggering of fewer inhibitory sensors (fat travelling a shorter length of gut as proximal absorption is increased). Therefore, in order to determine whether desensitization of the conuol of motilitv actuallv occurs. a chance in the motility response must be demonstra& acute&. In this study Gf 4 dogs, each equipped with duodenal and proximal jejunal fistulas along with 6 serosalelectrodes, desensitizationwas re-examined by comparing the response of jejunal motility following 1.5,2.5,3.5, or 4.5 h of steady state perfusion of an isolated 90 cm intestinal segment (between tistulas) with 30 n&l oleate at 1 ml/min. Intestinal motility was recorded during the last 0.5 h of each perfusion. Since spike burst activities correlate with contractions, a program was used to count the number of spike bursts that propagated (migrated across 2 or 3 electrodes) vs. those that were nonpropagated (NP, found in only 1 electrode). Perfusion duration iValues = means + SE) 4.5 h 2.5 h 3.5 h s I.5 h 448*22 222 2 17 365 + 76 318k 95 NP 386251 370 + 129 Total 501+ 17 247 + 15 1) Compared with the jejunal spike burst activity following 1.5 h of oleate perfusion, the response was markedly decreased with longer durations of steady state perfusion (1.5h vs. the average of 2.5-4.5 h: pc.05,.paiied t-test). 2) This difference in the motility response was especially significant between the 1.5 h and the 2.5 h experiments (pc.01. paired t-test). 3) The motility response partially recovered following 3.5 and 4.5 h of steady state perfusions. 4) The difference in the motility response was predominantly represented by changes in the number of nonpropagated spike bursts. We conclude that desensitization of intestinal motility to fat exposure occurs rapidly and may operate within the time frame of the immediate postprandial period. (Supported by Ross Laboratories Medical Nunition Services)
EFFECTS OF THYROTROPIN-RELEASING HORMONE (TRH) AND SEROTONIN (5-HT) ON VOLTAGE-DEPENDENT CURRENTS IN MOTONEURONES OF THE DORSAL MOTOR NUCLEUS OF THE VAGUS @MV). R.A. Travagli and R.A. Gillis. Department of Pharmacology. Georgetown University, School of Medicine, Washington D.C. 20007 The whole cell patch clamp technique was used to record voltage and current responses from v&ally identified DMV motoneurones after application of the putative neurotmnsmitters/neuromodulators TRH and 5-HT to the in vitre rat brainstem slice preparation. In initial studies, perfusion of the slice with either TRH or 5-HT using the cell attached recording mode, increased the spontaneous occurring discharge rate of these neurones. In the case of TRH, it reduced in a dose-related fashion (lO-1OOpM) the peak amplitude of the fast transient K+ current, I,. This occurred without any significant effect on either the activation or the inactivation curves of IA. TRH also produced a dose-related (10-1COpM) decrease in the peak amplitude of the apamin-sensitive Ca++ dependent K+ current, IAHP.Finally TRH was observed to produce an activation of a non specific inward cationic conductance. TRH did not exhibit any effect on the two hyperpolarization-activated currents, namely 1” and I, in this preparation. In the case of 5-HT, it reduced in a dose-related fashion (0.1-30 CM) the peak amplitude of the apamin-sensitive Ca-t + dependent K+ current, IAw, but had no significant effect on IA. This effect appeared to be exerted through activation of both 5X& and 5HT, receptors as determined by studies of specific agonists (2-methyl 5-HT, 1-Phenyl biguanide, mCPBG and 5-methoxytryptamine) and antagonist (MDL 72222) of these receptors. 5-HT also had no effect on I,,, and effects on IKIRremain to be done. In summary, both TRH and 5-HT excited DMV motomeurones in part by counteracting the apamin-sensitive Ca++ dependent K+ current, IAHp.In addition, excitation produced by TRH may also be due in part to a reduction in I, and to an increase in an inward cationic current. Due to lack of antagonists, the receptor mechanism responsible for TRH effects were not explored. In the case of 5-I-IT, the excitatory effect was mediated by activation of both 5-I-IT, and 5-HT, receptors.
ABSTRACTS OF PAPERS
COORJXNATION BETWEEN AND SYMPATHETIC CONTROL CONTRACTION AND ~$~LD~~CU)NIC
October 1992
NlXRICowlBIs -mSDRT -lNmItam Y.F. ti, N.W.
ll!KmJmIN~-KrrmIN ~almmrlm
Vlddmdt, Rrysiology. university a, TX 71030 Bperiments~ oxide @Way(s)
ELIPQRTCUFZEU)
F.G. m. Depts. of Surseryand of Texas Medical school at Ha&on.
designedto &kiy L--inine-nitric activities of intestinal in regulatw
ard m rmSdle in the rat ilamp. An Ussing modified (AmJ Rysiol 261:G166, 1991) so that astxaingage mcarldbeatta&zd lcqi~ly epithelium
chanker
rabbits and a serosal str.& iauge attached to measure CM contractions. Thepreip~y - -was play in an. orgy bath ;d r luminall perfused ~1 Krebs’ solutionat4mllmin Onea axsalt bridge e e&ode was laced m the bathing medmm and anot er inserted into a lumin outflow “T” iece onto which was tied the distal end of the colon. PD was measure4!between these electrodes. The
was
cmtbeeercealstiofilealsegments. m-three nwrkxd ae flat&e&a andvoltage cl@ at potential (FD) . Rzlaxation of the lorq’tudinal rmscle, previarsly mntracted by cd&z&o1 (10Jl4) , an3 &anqea in short circuit azrent (AI,,) in respcplse to B field etinulation (TFS) (5-secarrltrairrs of inpulses, 0.4 IRsinpllse durati No-nitro-Iraryinine @-ML) repeated. Tben,afterwashingan3addingL~3~~inine(LAF~S),TFSwaerepeatedagain. BothAI,,andnueclerelaxation m &own to be freqency dep~&&~ with max3nal VTtedata frequencyof 1OHz. Also, tetxdotaxin (5x10 ) blocked nuscle relaxation and m AI,, by 94% during TFS at 1OHz.
Maximal&lax OXINIL
spontaneous activity in a f uency-dependent manner. At the maximal stimulus strength ?+ e ects on tone were 71+ 19% (LM) and 71f 1396 (CM) (n =6) of the NE maximum. Activity returned to restin levels 11l* 11s (LM) and 47+24s (CM) after the termination of LCN!!. No consistent change in basal PD was observed with LCNS. but oscillations diminished wh& spontaneous muscle activity was abolished. CONCLUSIONS: 1. S ntaneous oscillations in PD and contractile activity occur concurren tp” y and this model may be useful in further investigatmg this phenomenon. 2. LCNS had a strong inhibitorv influence on contractile activitv. 3. The effects of NE and LCNS oii PD were mixed and their role in the control of colonic ion transport remains unclear. Supportedin partby Bgrantfrom the Cmh’s &
2624 I?4 ?? 26+4 E (5xlO.k) 62_+8* L-AX (5xlo‘sM) lOlk9 ** * significant differexe frcelall other grcap (pcO.05) ** significant differexe fmnallgzrap3exceptthe -1 (pCO.05) L+lNJ~blozkedthenuecle relaxation in3ucedbyTFS but
mediatingncnadrenergic,~linergicrelaxaticmMnot mediat~~inello*circuitaurent. (supportedby NIH resea&l grants GM38529, Ex38888)
Colitis Foundation of America.
ACUTE DESENSITIZATIONOF INTESTINALMOTILITY RESPONSE. H.C. Lin, Y.-G. Gu, J.H. Meyer. Depts. of Medicine, Cedars-Sinai Medical Center, Sepulveda VA Medical Center, UCLA, Los Angeles, CA. Acceleration of gastric emptying and omcecal transit were observed following prolonged exposure (14 days) to a high fat diet (Gut 1991;32:483). This effect was postulated to be the result of desensitization of the control mechanism for the motility of the gut. Since mucosal proliferation and enhanced proximal fat absorption may occur following protracted exposure to higher nutrient loads, such a change may result not from desensitization but from the triggering of fewer inhibitory sensors (fat travelling a shorter length of gut as proximal absorption is increased). Therefore, in order to determine whether desensitization of the conuol of motilitv actuallv occurs. a chance in the motility response must be demonstra& acute&. In this study Gf 4 dogs, each equipped with duodenal and proximal jejunal fistulas along with 6 serosalelectrodes, desensitizationwas re-examined by comparing the response of jejunal motility following 1.5,2.5,3.5, or 4.5 h of steady state perfusion of an isolated 90 cm intestinal segment (between tistulas) with 30 n&l oleate at 1 ml/min. Intestinal motility was recorded during the last 0.5 h of each perfusion. Since spike burst activities correlate with contractions, a program was used to count the number of spike bursts that propagated (migrated across 2 or 3 electrodes) vs. those that were nonpropagated (NP, found in only 1 electrode). Perfusion duration iValues = means + SE) 4.5 h 2.5 h 3.5 h s I.5 h 448*22 222 2 17 365 + 76 318k 95 NP 386251 370 + 129 Total 501+ 17 247 + 15 1) Compared with the jejunal spike burst activity following 1.5 h of oleate perfusion, the response was markedly decreased with longer durations of steady state perfusion (1.5h vs. the average of 2.5-4.5 h: pc.05,.paiied t-test). 2) This difference in the motility response was especially significant between the 1.5 h and the 2.5 h experiments (pc.01. paired t-test). 3) The motility response partially recovered following 3.5 and 4.5 h of steady state perfusions. 4) The difference in the motility response was predominantly represented by changes in the number of nonpropagated spike bursts. We conclude that desensitization of intestinal motility to fat exposure occurs rapidly and may operate within the time frame of the immediate postprandial period. (Supported by Ross Laboratories Medical Nunition Services)
EFFECTS OF THYROTROPIN-RELEASING HORMONE (TRH) AND SEROTONIN (5-HT) ON VOLTAGE-DEPENDENT CURRENTS IN MOTONEURONES OF THE DORSAL MOTOR NUCLEUS OF THE VAGUS @MV). R.A. Travagli and R.A. Gillis. Department of Pharmacology. Georgetown University, School of Medicine, Washington D.C. 20007 The whole cell patch clamp technique was used to record voltage and current responses from v&ally identified DMV motoneurones after application of the putative neurotmnsmitters/neuromodulators TRH and 5-HT to the in vitre rat brainstem slice preparation. In initial studies, perfusion of the slice with either TRH or 5-HT using the cell attached recording mode, increased the spontaneous occurring discharge rate of these neurones. In the case of TRH, it reduced in a dose-related fashion (lO-1OOpM) the peak amplitude of the fast transient K+ current, I,. This occurred without any significant effect on either the activation or the inactivation curves of IA. TRH also produced a dose-related (10-1COpM) decrease in the peak amplitude of the apamin-sensitive Ca++ dependent K+ current, IAHP.Finally TRH was observed to produce an activation of a non specific inward cationic conductance. TRH did not exhibit any effect on the two hyperpolarization-activated currents, namely 1” and I, in this preparation. In the case of 5-HT, it reduced in a dose-related fashion (0.1-30 CM) the peak amplitude of the apamin-sensitive Ca-t + dependent K+ current, IAw, but had no significant effect on IA. This effect appeared to be exerted through activation of both 5X& and 5HT, receptors as determined by studies of specific agonists (2-methyl 5-HT, 1-Phenyl biguanide, mCPBG and 5-methoxytryptamine) and antagonist (MDL 72222) of these receptors. 5-HT also had no effect on I,,, and effects on IKIRremain to be done. In summary, both TRH and 5-HT excited DMV motomeurones in part by counteracting the apamin-sensitive Ca++ dependent K+ current, IAHp.In addition, excitation produced by TRH may also be due in part to a reduction in I, and to an increase in an inward cationic current. Due to lack of antagonists, the receptor mechanism responsible for TRH effects were not explored. In the case of 5-I-IT, the excitatory effect was mediated by activation of both 5-I-IT, and 5-HT, receptors.