Chloride activity in cells of isolated perfused cortical thick ascending limbs of rabbit kidney

Muscle strips were excised from the circular and longitudinal layers of the fundus, corpus and antrum of canine stomach, and from the inner portion of the pyloric ring (inner pylorus). Substance P (SP) induced strong contractions, with the greatest sensitivity in fundus and circular corpus preparations (threshold near 10 -10 mol/l). The sensitivity to SP decreased in the sequence circular corpus - longitudinal antrum - circular antrum (threshold near 10(-7) mol/l); it re-increased towards the pylorus, and in the inner pylorus was nearly as high as in the fundus. The SP responses of fundus and longitudinal corpus were purely tonic, similar to acetylcholine (ACh) and histamine (H) responses. In circular corpus, SP induced a combined phasic-tonic response. SP induced in antrum strips purely phasic-rhythmical contractions of low frequency (similar to the H response), whereas ACh induced phasic contractions of high frequency, and in addition an increase of tone in the longitudinal antrum strips. The SP responses of the inner pylorus were not uniform; in some preparations purely tonic contractions were observed, and large phasic fluctuations of low frequency occurred in others. The phasic components of all the responses were completely suppressed by nifedipine (10(-6) mol/l). Tetrodotoxin as well as blockade of adrenoceptors, of ACh and of H receptors had no effect on the SP responses. Comparative studies with preparations from guinea-pig showed that species differences exist in the SP responses of gastric muscle.     

Effect of phorbol 12,13-dibutyrate on smooth muscle tone in rat stomach fundus.

We investigated the effects of phorbol 12,13-dibutyrate (PDBu), a typical protein kinase C (PKC) activator, on smooth muscle tone in the rat stomach fundus. In 5-hydroxytriptamine (5-HT)-precontracted stomach fundus strips, PDBu induced dose-dependent relaxation, but 4alpha-phorbol 12,13-didecanoate, a phorbol ester that does not activate PKC, did not induce relaxation. A PDBu-induced dose-dependent relaxation was also observed in strips precontracted with platelet-activating factor (PAF), carbachol, or 60 mM K+. In stomach fundus strips pretreated with PDBu, the contractile responses to 5-HT and PAF were completely blocked, but those induced by carbachol and endothelin-1 (ET-1) were only partially inhibited. In stomach fundus strips preincubated with carbachol in Ca2+-free medium, the Ca2+-induced contraction was decreased by preincubation with PDBu. In strips preincubated with 5-HT, PAF, or ET-1 in Ca2+-free medium, Ca2+-induced contractions were greatly inhibited by pretreatment with PDBu. These results suggest that in rat stomach fundus strips, PDBu-induced relaxation is mediated by activation of PKC. We speculate that a major factor mediating the relaxant action of PDBu in rat stomach fundus smooth muscle is represented by a reduction in Ca2+ influx via an inhibition of Ca2+ channels.     

Effects of endothelin,calcium channel blockade and EDRF inhibition on the contractility of human uteroplacental arteries

In order to examine the possibility that endothelin might be important in the regulation of placental blood flow, human uteroplacental vessels were superfused in vitro to study the contractile effect of endothelin as compared with a known strong contractor of placental blood vessels, serotonin (5-HT). The contractile responses were compared in the presence and absence of calcium channel blocking agents, as well as in the presence of L-NMA, an inhibitor of EDRF/nitric oxide. Endothelin (ET, 10^-5 10^-6 M) and 5-HT (10^-8-10^-4 M) induced contractions in the vessels. Maximal contractions in the presence of endothelin were elicited at 10^-7 M, whereas 5-HT elicited maximal contractions at 10^-5 M. At 10^-7 M, ET was more potent than 5-HT. The calcium-channel blocking agents nifedipine, diltiazem and NiCl₂ relaxed the vessels by 5–15% from baseline. The contractile response to ET in the presence of nifedipine or diltiazem was reduced by 55 and 67%, respectively. The response to 5-HT in the presence of nifedipine was reduced by 58%. The contractile response to 5-HT as well as ET in the presence of both nifedipine and NiCl₂ was not significantly lower than in the presence of nifedipine only. The EDRF-inhibiting agent L-NMA caused a small contractile response at concentrations of 10^-6–10^-5 M. ET as well as 5-HT added after pretreatment with L-NMA produced a larger contractile response than ET or 5-HT alone. The results show that ET has a strong contractile effect on placental blood vessels at concentrations likely to occur during labor and delivery. The mechanism whereby ET as well as 5-HT contracts placental vessel smooth muscle appears to partly involve nifedipine- and diltiazem-sensitive calcium channels, but almost half of the response depends on mobilization of calcium through other means.     

Role of different calcium pools in the contraction of respiratory smooth muscle

Contractions were evoked in isolated strips of rat trachea by potassium and acetylcholine (ACh) respectively. Extracellular calcium (Ca) was removed by EGTA and Ca influx was inhibited by diethylstilboestrol (DES). Contractions evoked by potassium were completely inhibited in the presence of EGTA or DES. ACh-induced contractions were rapidly abolished by EGTA whereas DES did not completely block these responses when a high concentration of ACh (10(-4) M) was used. Repeated activation by ACh in the presence of DES displayed two different phases of the contractile response; one initial brief contraction that decreased only slowly in the presence of DES, and a second phase with sustained contraction that was more readily depressed by DES. It is suggested that the smooth muscle in rat trachea is activated by Ca originating both intra- and extracellularly. As EGTA almost immediately blocked even the initial contractile response, the intracellular store is apparently located in or very close to the plasma membrane.     

Diabetes mellitus and responses of the urinary bladder to acetylcholine: an in vitro study

This study was prompted by the inconsistent reports and apparent controversies that exist in the biomedical literature on the responses of diabetic bladder strips to cholinergic nerve stimulation or exogenously-administered muscarinic agonists, especially acetylcholine (ACh). In the present study, acetylcholine-induced contractions of urinary bladders isolated from normoglycaemic (normal) and streptozotocin-treated, diabetic Wistar rats were examined under physiological conditions. Mechanical contractile changes of the isolated urinary bladders of STZ-treated, diabetic rats in response to bath-applied acetylcholine were compared with those obtained from isolated urinary bladders of normal, age-matched, control rats. Results obtained show that urinary bladders from diabetic rats were always more spontaneously active after mounting, than those of the age-matched normal, control rats. ACh (10(-8)-10 (-4) M) provoked concentration-related, atropine-sensitive contractions of the isolated urinary bladders of both diabetic and age-matched normal, control rats. However, acetylcholine always induced more powerful and greater contractions of the diabetic bladders compared with bladders from the age-matched normal, control rats. The magnitude and/or intensity of the diabetic bladder enhanced contractile responses to ACh continued to increase as the diabetic state of the animals progressed.     

Long term effects of septohippocampal lesions and intrahippocampal grafts on acetylcholine concentration,muscarinic stimulated formation of inositol phospholipids and electrically evoked release of neurotransmitters in the rat hippocampus

Summary Long Evans female rats sustained aspirative lesions of the septohippocampal pathways; subsequently, they received intrahippocampal suspension grafts of fetal septal-diagonal band or hippocampal tissue. The long term (8–10 months post-surgery) effects of these treatments were examined in the hippocampus for the following variables: concentration of hippocampal acetylcholine (ACh), muscarinic-stimulated (carbachol) formation of inositol monophosphate, accumulation of tritiated choline, noradrenaline (³H-NA) and serotonin (³H-5-HT), electrically evoked release of ³H-acetylcholine (³H-ACh), ³H-NA and ³H-5-HT, and choline acetyltransferase (ChAT) activity. The lesions decreased the levels of endogeneous ACh, the accumulation of ³H-choline and ³H-5-HT and the evoked release of both ³H-ACh and ³H-5-HT as well as the ChAT activity, but they failed to significantly affect the muscarinic-stimulated formation of inositol monophosphate and the accumulation and release of ³H-NA. Grafts of hippocampal cells were found to be ineffective on all lesion-induced effects. In contrast, grafts of septal-diagonal band origin attenuated the deficit of hippocampal concentrations of ACh and accumulation of ³H-choline without, however, improving release of ³H-ACh, accumulation and release of ³H-5-HT, and ChAT activity. These observations suggest that: (i) denervation-induced hippocampal muscarinic supersensitivity might not be long-lasting or the lesions, which in some cases spared the lateral edges of the fimbria, failed to induce any muscarinic supersensitivity, (ii) intrahippocampal grafts rich in cholinergic neurons do not foster recovery from the lesion-induced noncholinergic deficits we assessed, (iii) recovery of function may be expressed by some but not all biochemical or pharmacological cholinergic variables and (iv) graft-derived hippocampal reinnervation may be less efficient than the endogenous innervation of intact rats as indicated by the restoration of only some of the variables related to cholinergic function by intrahippocampal septal-diagonal band grafts.     

Endocrine response to acute cold exposure by lactating and non-lactating Norway rats

Plasma levels of corticosterone, prolactin and thyroxine (T4) were measured in lactating and non-lactating Norway rats at 22 degrees C and 4 degrees C. Acute cold exposure increased corticosterone secretion in all groups, although non-lactating female levels rose higher than those of mother rats. While prolactin levels are unaffected by acute cold exposure in non-lactating females, mothers with their litters had lower prolactin levels in the cold. T4 levels increased during cold exposure in lactating females, suggesting that the low T4 levels observed during lactation may not be due to lactational competition for available iodine.     

5-Hydroxytryptamine receptor characterizations of human cerebral,middle meningeal and temporal arteries: regional differences

We have studied the regional distribution of 5-hydroxytryptamine (5-HT) receptor subtypes in fresh circular segments of human cerebral, middle meningeal, and temporal arteries. Vasomotor responses induced by a series of 5-HT agonists and antagonists with some degree of selectivity were studied by using a sensitive in vitro system. Nine 5-HT agonists were examined for contractile effects on the arteries. In cerebral and meningeal arteries 5-carboxamidotryptamine (5-CT) was more potent than 5-HT. The opposite order of potency (5-HT-5-CT) was found in temporal arteries. In the cerebral arteries 5-methoxytryptamin (5-MeOHT) was more potent than sumatriptan while sumatriptan was more potent than 5-MeOHT in meningeal and temporal arteries. The 5-HT₁, receptor antagonist, methiothepin, competitively antagonized 5-CT-induced contractions in cerebral arteries, with a _P^A₂, value of 9.05. 5-HT-induced contractions were competitively antagonized by ketanserin (5-HT₂) in the temporal arteries _PA₂, value of 9.06). Methiothepin and ketanserin had non-competitive antagonistic effects in the middle meningeal arteries. The 5-HT₃, selective antagonist ondansetron did not cause any shift of the contractions induced by 2-methyl-5-HT in the temporal, cerebral and middle meningeal arteries. These results suggest that the cerebral arteries mainly contain 5-HT_id., or 5-HT₁,-like receptors, and the temporal artery 5-HT₂, receptors; the data further indicate the presence of both receptor subtypes in the middle meningeal artery.     

Effect of serotonin and histamine on cell contractility in the internal carotid artery

Experiments on isolated segments of the dog internal carotid artery showed that serotonin (5-HT), in a concentration of 5·10^–11 to 5·10^–5 g/ml, activates contractions. Histamine in a concentration of 5·10^–9 g/ml causes relaxation of the segments, but higher concentrations activate contractile responses. 5-HT and histamine were found to evoke contractile responses of depolarized vascular smooth muscle. It is suggested that 5-HT activates the inward calcium ion current through the membrane whereas histamine activates both the inflow of extracellular calcium and the outflow of calcium ions from the intracellular depots.Department of Normal Physiology, Leningrad San.-Gig. Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 7, pp. 3–5, July, 1979.     

Brain stimulation enables the solution of an inherently difficult problem

Lactating female rats show a maternal anxiolysis signal, which is part of the behavioral pattern that develops post-partum and seems to be related to hormonal changes during lactation. Assuming that glucocorticoids modulate prolactin and oxytocin secretion, we evaluated the effect of dexamethasone on behavior responses of fear and anxiety in lactating rats. For this study, the non-lactating and lactating rats were submitted to an elevated T-maze and open field tests. In the elevated T-maze, the lactating rats showed a decrease in inhibitory avoidance and an increase in the escape time when compared with the non-lactating group. The lactating rats that had been treated with dexamethasone showed increased initial avoidance latency when compared with lactating rats treated with vehicle. The same result was found in the subsequent repetitions (avoidance 1 and 2). In addition, there was a reduction in one-way escape time for the lactating rats that were treated with dexamethasone. The lactating rats treated with vehicle had increase of number central entries, and consequently, the anti-thigmotactic effect increased relative to non-lactating rats. Thus, lactating rats showed a reduced emotional responsiveness as evaluated by elevated T-maze and open field tests, which characterizes maternal anxiolysis. In addition, it could be concluded that the dexamethasone impairs maternal anxiolysis in lactating female rats.     

Blockade of nitric oxide decreases the renal vasodilatory effect of neuropeptide Y in the insulin-treated diabetic rat

 The effect of 50 days of streptozotocine-induced diabetes mellitus (blood glucose 20 mmol/l) on contraction and relaxation of isolated renal and intrarenal arteries in rats were examined. Strong and similar contractions were induced by potassium (60 mM), 5-hydroxytryptamine (5-HT) and endothelin-1 (ET-1) in renal and intrarenal arteries in diabetic and control rats. The vasodilatory reactivity, after precontraction with 5-HT, of neuropeptide Y (NPY) was similar to that of acetylcholine (ACh), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) and was similar in diabetic and control rats. The relaxing effect of NPY was decreased (40%) only in the diabetic group by blockade of nitric oxide synthase with N ^G-nitro-L-arginine methyl ester (10^–4 M) and by blockade (50%) of NPY with α-trinositol (10^–6 M). In conclusion, the present study showed that diabetes mellitus in the rat is associated with normal vasoconstrictive and vasodilatory capacities. However, the vasodilatory response to NPY was largely eliminated by blockade of nitric oxide synthesis only in the diabetic animals. This indicates that the vasodilatory effect of NPY in diabetes mellitus may be dependent on nitric oxide synthesis. Received: 12 November 1996 / Received after revision: 10 March 1997 / Accepted: 7 April 1997     

Role of the endothelium in regulation of vascular functions in two teleosts

Functional and structural aspects of the vascular endothelium were studied in major blood vessels from two distantly related species, the Atlantic salmon (S. salar) and the cod (G. morhua.) The ventral aorta (VA) of both teleosts and the dorsal aorta (DA) and the coeliaco mesenteric artery (CMA) of the cod and the salmon respectively were examined for endothelium dependent and independent responses to acetylcholine (ACh), adrenaline (A) and endothelin–1 (ET–1). In the salmon, endothelial probing resulted in reduced contractile responses to high K⁺ in both VA and CMA while the responses to ACh and A were reduced only in CMA. Indomethacin, but not L–NMMA, enhanced vasoconstrictions to high K⁺, ACh and A in the unprobed CMA. In the cod vessels the endothelial probing caused reduced contractile responses to the two effective vasoconstrictors in both vessels, to high K⁺ and A in VA and to high K⁺ and ET–1 in DA. Both indomethacin and L–NMMA enhanced contractile tension to A in VA, while indomethacin, but not L–NMMA, enhanced the constrictions by high K⁺ in VA and by ET–1 in DA. These experiments have revealed heterogeneous patterns of endothelial function in blood vessels of two teleosts, reflecting differences in endothelial morphology and in production of potent endothelial derived contracting factors as well as prostanoic and non–prostanoic endothelium–derived dilating factors.     

Contractile profile of esophageal and gastric fundus strips in experimental doxorubicin-induced esophageal atresia

Esophageal atresia (EA) is characterized by esophageal and gastric motility changes secondary to developmental and postsurgical damage. This study evaluated the in vitro contractile profile of the distal esophagus and gastric fundus in an experimental model of EA induced by doxorubicin (DOXO). Wistar pregnant rats received DOXO 2.2 mg/kg on the 8th and 9th gestational days. On day 21.5, fetuses were collected, sacrificed, and divided into groups: control, DOXO without EA (DOXO-EA), and DOXO with EA (DOXO+EA). Strips from the distal esophagus and gastric fundus were mounted on a wire myograph and isolated organ-bath system, respectively, and subjected to increasing concentrations of carbamylcholine chloride (carbachol, CCh). The isolated esophagus was also stimulated with increasing concentrations of KCl. In esophagus, the concentration-effect curves were reduced in response to CCh in the DOXO+EA and DOXO-EA groups compared to the control group (P<0.05). The maximum effect values (E_max) for DOXO+EA and DOXO-EA were significantly lower than control (P<0.05), but the half-maximal effective concentration (EC₅₀) values were not significantly different when the three groups were compared (P>0.05). In response to KCl, the distal esophagus samples in the three groups were not statistically different with regard to E_max or EC₅₀ values (P>0.05). No significant difference was noted for EC₅₀ or E_max values in fundic strips stimulated with CCh (P>0.05). In conclusion, exposure of dams to DOXO during gestation inhibited the contractile behavior of esophageal strips from offspring in response to CCh but not KCl, regardless of EA induction. The gastric fundus of DOXO-exposed offspring did not have altered contractile responsiveness to cholinergic stimulation.     

Actions of SQ 29,548 on contractile responses and arachidonic acid metabolism of intrapulmonary arteries,in vitro

This study was undertaken to investigate the influence of SQ 29, 548, a thromboxane (TX) A₂ receptor antagonist, on contractile responses and arachidonic acid (AA) metabolism of bovine intrapulmonary arterial (IPA) rings. The contractile responses to 5-hydroxytryptamine (5-HT), histamine, phenylephrine, and potassium chloride (KCl) were not significantly altered by 10^–8 M SQ 29, 548 in either endotheliumintact or denuded IPA. The concentration of SQ 29,548 was chosen as it reduced the response to 10^–7 M U46619, a TXA₂ mimetic, by 50%. AA metabolism by IPA produced more PGI₂ whereas that by intrapulmonary vein (IPV) produced more PGE₂. SQ 29,548 in concentrations of 10^–8 to 10^–5 M did not affect the activity of PGI₂ synthase or GSH-dependent PGE₂ isomerase in IPA or IPV microsomal fractions. No microsomal TXA₂ synthase activity was detectable. SQ 29,548 had no effect on PGH synthase activity of IPA or IPV. The data indicate the presence of a TXA₂-mediated contractile response in the IPA which is endothelium-independent and is selectively antagonized by SQ 29,548. The data further indicate that the contractile responses of IPA to 5-HT, histamine, phenylephrine, and KCl do not have a TXA₂-mediated component. It is suggested that SQ 29,548 is a pharmacological probe to determine the role of TXA₂ n pathophysiologic states in the pulmonary vascular bed and may be a therapeutic agent to treat pulmonary hypertensive disorders in which TXA₂ is involved.     

Role of prolactin in the regulation of some liver cell functions after ligation of common bile duct

In rats with ligated common bile duct, the inhibitor of prolactin secretion bromocriptine inhibited proliferation of bile ducts in males, reduced Na⁺ concentration in bile in females, and elevated blood bilirubin. In males with pituitary transplants, proliferation of bile ducts increased. It was concluded that the effects of prolactin on cholangiocyte proliferation and bile ion content after ligation of the common bile duct are sex-dependent. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny Vol. 127, No. 5, pp. 573–575, May, 1999     

Effects of transmural field stimulation in isolated muscle strips from rabbit sphincter of Oddi and duodenum

The purpose of the study was to compare the effect of transmural field stimulation (TMS) on isolated smooth muscle strips from rabbit sphincter of Oddi (SO), duodenal circular layer (D_c) and duodenal longitudinal layer (D. The strips were suspended in thermostatically controlled 5-ml organ baths containing Krebs solution constantly bubbled with 5% CO_a in 0₂. TMS was delivered through platinum electrodes (140 V, 0.4 ms, 5 s trains, 40 Hz). The TMS responses could be divided in two main responses: (1) contraction initiated after cessation of the stimulus train, preceded by an inhibitory phase during TMS (‘off’); and (2) contraction initiated during TMS (‘duration’). The ‘duration’ response was observed in one out of 20 strips in the SO and D_c compartments, whereas 11 D, strips (55%) showed ‘duration’ responses (P < 0.001). Atropine (10^-6) converted all ‘duration’ responses to an ‘off’ response preceded by an inhibitory phase during TMS and reduced the contractile amplitudes with 40–65%. L-NNA significantly increased the number of ‘duration’ responses in all types of muscle, and caused a 40% increase in Dj contractile amplitude. Inhibitory responses could not be removed by atropine, propranolol and phentolamine. The results suggest that the intrinsic innervation of SO and duodenal muscle consists of a mixture of excitatory, cholinergic and inhibitory NANC pathways. The latter may utilize, wholly or partly, NO or a related compound as transmitter. A relative dominance of excitatory, cholinergic responses was present in the D_: strips, whereas inhibitory responses were dominating in the SO and D_c strips.     

Prostaglandin endoperoxides,serotonin and the superfused rabbit aorta: Possible pitfalls in the bio-assay of rabbit aorta contracting substance (RCS)

The specificity of the isolated rabbit aorta for identification and assay of prostaglandin endoperoxides, formed during aggregation of platelet rich plasma (PRP) from rats, was investigated in the superfused organ cascade. The use of cumulative dose-response curves in this design is quicker than conventional step-wise dosing while delivering identical results. On the rabbit aorta, in contrast to the rat fundus strip, methysergide is too weak an antagonist to rule out responses due to 5-HT. After pretreatment with phenoxybenzamine, in the presence of methysergide, the rabbit aorta retains its sensitivity towards oxygenated fatty acids, while being virtually unreactive towards 5-HT. The prostaglandin endoperoxide PGH₂ is more potent than prostaglandin E₂ when assayed on the rabbit aorta, while on the rat fundus the situation is reversed. Combining the rabbit aorta and rat fundus strip with pre-filtration on Amberlite^® XAD-2 columns showed that during collagen induced aggregation rat PRP generated both a labile RCS-most probably a prostaglandin endoperoxide—and a lipophylic prostaglandin-like material, along with 5-HT.     

Developmental changes in contraction of gastric smooth muscle cells in rats correlate with their differences in RhoA/ROCK pathway

Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes relate to differences in the expression and/or activity of the key enzymes regulating smooth muscle contraction has not been previously evaluated. Therefore, we aimed to examine the expression and activation of the small monomeric G protein "RhoA" and Rho kinase (ROCK) as well as their correlation with the contraction of gastric smooth muscle cells (GSMCs) in newborn vs. adult rats. Freshly isolated single GSMCs from Sprague-Dawley rats at 1 week (newborn) and 3 months (adult) of age were used in the study. Protein and mRNA expression levels of both ROCK2 and total RhoA were higher in adult compared to newborn rats. Moreover, acetylcholine (ACh)-induced contractions of GSMCs in adult rats were significantly higher than that in newborn animals. Meanwhile, ROCK and Rho activation was higher in adult stomach cells compared to newborn ones. Pretreatment of GSMCs with Y-27632, the ROCK inhibitor, significantly reduced ACh-induced contraction in both groups of cells and greatly abolished contractile differences. In conclusion, our results indicate that RhoA/ROCK pathway and contraction of stomach muscle cells are under developmental regulation.     

Difference in signal transduction mechanisms involved in 5-hydroxytryptamine- and U46619-induced vasoconstrictions.

In order to elucidate the signal transduction pathways of vascular smooth muscle contractions induced by stimulation of receptors for 5-hydroxytryptamine (5-HT) and thromboxane A2 (TXA2), both of which are released from activated platelets, we examined whether protein kinases, such as tyrosine kinase, p38 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC), are involved in the contraction produced by either 5-HT or U46619 (an analog of TXA2) in the rat aorta. Both 5-HT and U46619 induced sustained contractions, which were markedly reduced in the absence of extracellular Ca2+. Verapamil (a L-type Ca2+ channel blocker) markedly inhibited the contractile response to 5-HT, while the U46619-induced contraction was only slightly inhibited by verapamil. Both contractile responses to 5-HT and U46619 were significantly inhibited by calphostin C (a PKC inhibitor). On the other hand, both genistein (5 microM, a tyrosine kinase inhibitor) and SB203580 (a p38 MAPK inhibitor) significantly inhibited 5-HT-induced contractions but had little effects on the contractions induced by U46619. These results suggest that the signal transduction mechanisms involved in the contractions mediated via 5-HT and TXA2 receptors are different as follows. Both the tyrosine kinase and p38 MAPK pathways are involved in 5-HT contraction but not in TXA2 contraction, while both contractions are strongly dependent on transplasmalemmal Ca2+ entry. The contractile responses to both 5-HT and TXA2 involve voltage-dependent Ca2+ channels and PKC.     

Efflux of 5-Hydroxytryptamine from Synaptosomes of Rat Cerebral Cortex

The efflux of ³H-5-HT from a crude synaptosome preparation of the cerebral cortex of reserpinized rats was examined. The synaptosomes were loaded with ³H-5-HT by pre-incubation of the homogenate in presence of pargyline and desipramine in order to inhibit deamination of 5-HT and uptake into noradrenergic neurones. The synaptosomes were collected by centrifugation, washed and resuspended in 0.25 M sucrose. No spontaneous efflux of 5-HT was detectable at 0°C but marked efflux was observed at 27°C and 37°C. 4-Chloroamphetamine, low external Na⁺ concentration, ouabain and the depolarizing agent veratridine markedly accelerated the initial (5 min) efflux. Inhibitors of the neuronal 5-HT uptake, e.g. chlorimipramine, H 102/09 and A 23189, antagonized the 5-HT efflux evoked by these means, whereas desipramine, which is a poor inhibitor of the 5-HT uptake, had only slight effect on the 5-HT efflux. It is suggested that 5-HT can be actively transported out from the synaptosomes by the reversed 5-HT uptake mechanism.