Rat Portal Vein Research Articles

Effects of ischemia on intracellular sodium and phosphates in the in vivo rat liver.

Metabolic factors that influence the transition form reversible to irreversible ischemic injury were studied in the rat liver in vivo with 31P-nuclear magnetic resonance (NMR) spectroscopy. Hepatic ischemia for 15, 35, or 65 min was produced by occlusion of the hepatic artery and portal vein in rats. Ischemia caused a rapid decrease in the ATP concentration ([ATP])-to-P(i) concentration ratio and pH within 5 min, but there was little change in these variables detectable by 31P-NMR with longer periods of ischemia. After reperfusion, the [ATP] and P(i) concentration returned toward normal values in livers exposed to 15 or 35 min of ischemia, but 65 min of ischemia were associated with only modest recovery in [ATP], and the [ATP] later decreased. Because the 31P-NMR spectrum was similar after brief compared with prolonged ischemia, it appears that neither ATP depletion, P(i) accumulation, nor acidosis predicts metabolic recovery. Hepatic intracellular NA+ was also measured in separate groups of animals by 23Na-NMR in the presence of a shift agent, thulium (III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene-phosphonate) (TmDOTP5-), and by atomic absorption spectroscopy. Under baseline conditions, the concentration of intracellular Na+ was 15.2 mM by atomic absorption spectroscopy and 16.5 mM by 23Na-NMR. Although the 31P-NMR spectrum responded very rapidly to the onset of ischemia, intracellular Na+ concentration measured by 23Na-NMR increased gradually but steadily at approximately 1.0 mM/min during early (up to 15 min) ischemia. These observations demonstrate that a rise in intracellular Na+ does occur early ischemia, that TmDOTP5- can be applied in vivo for analysis of intracellular Na+ in the ischemic liver, and that 31P-NMR spectroscopy is very sensitive to early ischemic injury.

Modulation of vascular K ATP channels in hypothyroidism

The role of vascular K ATP channels in hypothyrodism-induced decrease in myogenic activity of rat portal vein was examined by using pharmacologically relevant concentrations of K + channel ligands. As compared to controls, a significant decrease in the myogenic tone and noradrenaline (10 −9–10 −5 M)-induced contractions was observed in portal veins from hypothyroid rats. In both euthyroid and hypothyroid states, pinacidil (10 −9–10 −5 M) and cromakalim ((10 −9–10 −5 M) caused concentration-related inhibition of the myogenic tone (frequency and amplitude). However, hypothyroidism caused a leftward shift in the concentration-response curves of the K + channel openers with a corresponding decrease in their IC 50 values both in the absence and presence of the K ATP channel blocker, glibenclamide (10 −7 M). Further, concentration-dependent increase in the frequency of myogenic tone by glibenclamide (10 −8–3 × 10 −6 M) was greater in tissues from hypothyroid rats (EC 50 = 2.07 × 10 −7 M; 95% CL, 1.06−4.05 × 10 −7 M) in comparison to controls (EC 50 = 8.07 × 10 −7 M; 95% CL, 0.53−1.22 × 10 −6 M). These results suggest that a decrease in the myogenic tone of rat portal vein may possibly be related to an enhanced opening of the K ATP channels in hypothyroidism.

Two types of ATP-sensitive potassium channels in rat portal vein smooth muscle cells.

1. Single-channel recordings were made from single, enzymatically isolated smooth muscle cells of rat portal vein by the patch-clamp technique. 2. Unitary potassium currents were identified through two types of K-channels with conductances in 60:130 mM K-gradient of 50 and 22 pS; these are referred to as LK and MK channels respectively. 3. The LK channels became extremely active if isolated patches were created into nucleotide-free solution; activity was inhibited by ATP applied to the inner surface of the patch with a half maximal inhibition (Ki) of 11-23 microM. Channel activity declined and disappeared with time and could be regenerated by a brief application of Mg-ATP or a nucleoside diphosphate such as UDP (in the presence of Mg). LK channel activity was rarely stimulated by levcromakalim and not by pinacidil (K-channel openers, KCOs) but was blocked by glibenclamide. 4. Activity of MK channels declined if isolated patches were created into nucleotide free solution; activity reappeared if UDP or ATP alone (in the presence of Mg) was applied; pinacidil or levcromakalim in the presence of ATP or UDP further increased channel activity which was blocked by glibenclamide. 5. The LK channel inhibited by ATPi is very similar in its conductance and other properties to the KATP channel described in tissues other than smooth muscle, in its conductance and properties the MK channel resembles the KNDP channel we have previous described as present in other smooth muscles and opening in responses to KCOs.

Angiotensin II-activated Ca2+ entry-induced release of Ca2+ from intracellular stores in rat portal vein myocytes.

1. The action of angiotensin II (AII) was studied in single myocytes from rat portal vein in which the cytoplasmic Ca2+ concentration was estimated by emission from dyes Fura-2 or Indo-1 and the Ca2+ channel current was measured with the whole-cell mode of the patch-clamp technique. 2. Most of the AII-evoked increases in [Ca2+]i were reduced by about 60% after pretreatment with ryanodine and caffeine to deplete intracellular Ca2+ stores. However, in some cells the AII-induced Ca2+ responses were of small amplitude and resembled those obtained in the presence of ryanodine and caffeine. Both types of Ca2+ responses induced by AII were selectively inhibited by losartan, suggesting that the AII effects resulted from activation of the angiotensin AT1 receptors. 3. The concentration-response curve to AII had an EC50 value close to 1 nM for the increase in [Ca2+]i obtained after depletion of intracellular Ca2+ stores. This value was increased to around 18 nM in experiments where the intracellular Ca2+ stores were not depleted. 4. AII-evoked Ca2+ responses were abolished in the absence of external Ca2+ and in the presence of 1 microM oxodipine to block L-type Ca2+ channels. 5. Intracellular applications of the InsP3 receptor antagonist, heparin or an anti-PdtIns antibody did not modify AII-induced Ca2+ responses. 6. Our results show that AII releases Ca2+ from intracellular stores without involving InsP3 but through a Ca2+ release mechanism activated by Ca2+ influx through L-type Ca2+ channels.

Activation of Calcium Sparks by Angiotensin II in Vascular Myocytes

Contraction in smooth muscle is triggered by an increase in cytoplasmic free calcium ([Ca2+]i) which depends on both Ca2+influx through L-type Ca2+channels and Ca2+release from the sarcoplasmic reticulum (SR). Two mechanisms have been shown to be involved in SR Ca2+release. one is stimulated by Ca2+and involved ryanodine-sensitive Ca2+-release channels; the other is stimulated by an increase in inositol 1,4,5-trisphosphate (InsP3) generation induced by various mediators and involved InsP3-sensitive Ca2+release channels. Here, we examined the effects of angiotensin II on [Ca2+]iin single rat portal vein myocytes using both the whole cell patch-clamp method and a laser scanning confocal microscope. Elementary Ca2+release events (Ca2+sparks) were obtained spontaneously or in response to L-type Ca2+channel current activation, and resulted from activation of ryanodine-sensitive Ca2+-release channels in the SR. We show that angiotensin AT1receptors stimulate Ca2+sparks through activation of L-type Ca2+channels without involving InsP3-induced Ca2+release. This novel transduction pathway may be a common mechanism for vasoconstrictors which do not stimulate generation of chemical second messengers.

Depolarization-evoked increases in cytosolic calcium concentration in isolated smooth muscle cells of rat portal vein.

1. Ca2+ current through voltage-dependent Ca2+ channels (ICa) and intracellular free Ca2+ concentration ([Ca2+]i) were measured simultaneously in rat portal vein smooth muscle cells using conventional whole-cell voltage clamp technique and high temporal resolution microfluorimetry. 2. The relationship between depolarization-evoked ICa and rise in [Ca2+]i was examined. The extracellular Ca2+ concentration dependence and the voltage dependence of the depolarization-evoked increases in ICa and [Ca2+]i were similar. Both ICa and increased [Ca2+]i were blocked to a similar extent by nimodipine and cadmium and augmented by Bay K 8644. Furthermore, the time course of the measured increase in [Ca2+]i, closely followed the increase in [Ca2+]i expected from the time-integrated ICa. These observations suggest that the depolarization-evoked rise in [Ca2+]i was tightly coupled to ICa. 3. The cytosolic Ca2+ buffering capacity, determined as the ratio of the expected increase in [Ca2+]i (from ICa) divided by the measured increase in [Ca2+]i, was over 100. Therefore, less than 1 out of 100 Ca2+ ions entering the cell appears as a free Ca2+. 4. Ryanodine (30 microM), a blocker of the Ca(2+)-induced Ca2+ release mechanism, had little effect on buffering capacity measured over the first 200 ms of the depolarizing voltage clamp pulse. Ryanodine also had little effect on the buffering capacity during 800-1000 ms of the depolarizing voltage clamp pulse. Therefore, it was concluded that there is little Ca(2+)-induced Ca2+ release from the stores in rat portal vein smooth muscle cells during depolarization-evoked Ca2+ entry. 5. During brief depolarizations, the largest [Ca2+]i increase and ICa occurred at 0 mV. However, during steady-state depolarization, the largest increase in [Ca2+]i occurred around -30 mV, and we estimate the peak steady-state ICa to be about 0.6 pA.

Decreased vascular reactivity of portal vein in rats with portal hypertension

Background/Aims: Vascular hyporesponsiveness in portal hypertension is well documented in the arterial tissue. The present study aimed to investigate the possible changes in the portal vein from portal hypertensive rats. Methods: Portal hypertension was induced by partial portal vein ligation. Fourteen days after surgery, portal veins were removed for contractile study and measurement of cAMP, cGMP and [Ca 2+] i. Results: In vitro tension preparation showed a decreased maximum response to nonrepinephrine in portal vein of portal vein ligated rats (38.3±4.1 vs. 23.4±1.5 mN/mm 2). The pA 2 values of WB4101 and yohimbine ( a 1- and a 2-adrenoceptor antagonist, respectively) were not different between the two groups. Tissue cAMP (14.4±0.9 vs. 12.2±0.7 pmol/mg protein), but not cGMP, content was increased and intracellular calcium [Ca 2+] i levels (247±9 vs. 281±13 nM) were decreased in portal vein ligated rats. Conclusions: These results showed that in portal vein from portal vein ligated rats, vascular hyporesponsiveness and an increase in basal cAMP content and a decrease in basal [Ca 2+] i were observed.

Absorption of tea catechins into rat portal vein.

Following the oral administration of tea catechins, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate, respectively, to rats, the presence of these catechins in the portal blood was examined. It was confirmed by HPLC and mass spectrometry analysis that each of the administered catechins was present in the blood. These results clearly indicate that four predominant catechins in fresh tea leaves are absorbed, at least in part, into the rat portal vein.

Investigation of the effects of 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) on membrane currents in rat portal vein.

1. The effects of 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) were investigated on evoked and spontaneous currents in freshly-isolated cells from the rat portal vein by use of conventional whole-cell recording and perforated-patch techniques. 2. At a holding potential of -60 mV in potassium-free, caesium-containing solutions, NPPB (10 microM) inhibited calcium (Ca)-sensitive chloride currents (ICl(Ca)) evoked by caffeine (10 mM) and by noradrenaline (10 microM) by 58% and 96%, respectively. 3. At a holding potential of -2 mV in potassium (K)-containing solutions, NPPB (10 microM) inhibited charybdotoxin-sensitive K-currents (IBK(Ca)) induced by noradrenaline (10 microM) and acetylcholine (10 microM) by approximately 90%. In contrast, IBK(Ca) induced by caffeine (10 mM) was unaffected in the presence of NPPB (10 microM). Conversely, IBK(Ca) elicited by caffeine (2 mM) was reduced by approximately 50% whereas IBK(Ca) evoked by noradrenaline (50 microM) was not significantly inhibited by NPPB. 4. In K-containing solutions, NPPB (10 microM) abolished spontaneous transient outward currents (STOCs) and induced a slowly-developing outward K-current. Bath application of glibenclamide (10 microM) abolished the outward current but did not antagonize the inhibitory effects of NPPB on STOCs or on IBK(Ca) evoked by noradrenaline. 5. In caesium-containing solutions, NPPB (30 microM) inhibited voltage-sensitive Ca-currents. 6. In Ca-free, K-containing solutions and in the presence of glibenclamide (5 microM), IBK(Ca) induced by 20 microM NS1619 was enhanced by NPPB (10 microM). 7. It is concluded that NPPB inhibits agonist-induced ICl(Ca) in rat portal vein smooth muscle. However, this agent also inhibits agonist-evoked IBK(Ca) and STOCs. Moreover, NPPB inhibits voltage-sensitive Ca-currents and stimulates a glibenclamide-sensitive K-current and IBK(Ca). The effects of this agent on evoked ICl(Ca) and IBK(Ca) and on STOCs probably involves an inhibitory action on intracellular Ca-stores.

Assessment of the in vivo hepatic lysosomal processing of horseradish peroxidase

The lysosomal processing of horseradish peroxidase (HRP) was assessed in this study, i.e., its lysosomal proteolysis and the biliary output of its possible lysosomal metabolites by rat liver in vivo. HRP was covalently linked to [14C]sucrose to provide a label that remains trapped within lysosomes after proteolysis. The [14C]sucrose-labelled HRP was injected into the portal vein of rat, and after 30 min about 34% of the injected radiolabel was present in the liver. Subcellular fractionation by differential centrifugation and further purification of lysosomes in a Percoll gradient showed that radiolabel was concentrated in lysosomes and indicated that about 91% of the total proteolysis of HRP in liver could be attributed to these organelles. The in vivo lysosomal degradation rate of HRP at 30 min was about 40%/h, decreasing over time. The lysosomal inhibitors chloroquine and leupeptin suppressed proteolysis of HRP by about 30 and 60%, respectively. Analysis of the 14C excreted in bile by trichloroacetic acid precipitation and by SDS-polyacrylamide gel electrophoresis showed a minor fraction, which was intact HRP (40 kDa), and a major fraction, which was associated with material smaller than 3 kDa. The biliary output of these low molecular mass products, in contrast to that of intact HRP, did not gradually decline with time and represented about 3% of the corresponding amounts in liver. Chloroquine and leupeptin specifically decreased their biliary excretion (about 60%), giving additional support to their lysosomal origin. In addition, the overall hepatic processing of [14C]sucrose-labelled HRP did not differ from that of the native HRP measured by enzyme assay, indicating no significant alteration caused by the labelling procedure.

CGRP innervation and receptors during aging of male and female hepatic rat portal veins

Calcitonin gene-related peptide (CGRP) innervation and binding sites were studied on hepatic portal veins of male and female rats from 19 days to 22 months of age. CGRP containing nerve fibers were present both in adventitial and medial nerve plexuses, closely apposing to or penetrating into the muscular layers. The density of CGRP innervation was estimated on whole mount preparations and compared during aging. In females, aging did not affect the number of fibers per unit length, although the vessel circumference decreased after 6 months of age. In males, the vessel circumference remained constant during aging, while the density of innervation significantly decreased. Whatever the age or sex of the animals was, no CGRP binding sites were found on portal veins sections by autoradiography. CGRP had no effect on spontaneous contractions of perfused portal veins. The difference observed in the evolution of CGRP innervation density between males and females suggests that CGRP innervation in the rat portal vein may be influenced by gonadal steroids during aging.

Effects of Phospholipase C Inhibitors on Ca2+Channel Stimulation and Ca2+Release from Intracellular Stores Evoked by α1A- and α2A-Adrenoceptors in Rat Portal Vein Myocytes

The ability of phospholipase C inhibitors to inhibit Ca2+channel stimulation and Ca2+release from intracellular stores evoked by norepinephrine in single rat portal vein myocytes was investigated in the aim of identifying the type of phospholipase C involved in the transduction pathways activated by α1A- and α2A-adrenoceptors. U73122 (an inhibitor of phosphatidylinositol-phospholipase C) inhibited in a concentration-dependent manner the release of Ca2+from the intracellular stores induced by activation of α1A-adrenoceptors and related to inositol phosphate production whereas U73343 was ineffective. Both compounds had no effect on the release of Ca2+induced by caffeine. However, U73122 and U73343 inhibited the L-type Ca2+channel. D609 (an inhibitor of phosphatidylcholine-phospholipase C) had no direct inhibitory effects on the L-type Ca2+channel but it inhibited concentration dependently the α2A-adrenoceptor-induced stimulation of Ca2+channels, which had been shown to be independent of phosphatidylinositol hydrolysis. Therefore, these results suggest that α2A-adrenoceptors activate a phosphatidylcholine-phospholipase C in vascular myocytes. However, D609 had other sites of action as it blocked norepinephrine- and caffeine-induced Ca2+release from the intracellular stores.

Distribution of Endothelin-1-Receptor Subtypes in Rat Portal Vein

Endothelin-1 (ET-1), a potent vasoactive peptide, was first isolated from cultured porcine endothelial cells. Subsequent studies revealed the existence of two additional related peptides, ET-2 and ET-3, and at least two distinct ET-receptor subtypes, ETA (selective for ET-1) and ETB (nonselective for ET isopeptides). These isopeptides and receptors are widely distributed in many tissues and are involved in numerous biological responses. The aim of this study was to identify the eventual distribution of the two distinct endothelin-receptor subtypes in isolated endothelium-denuded rat portal vein rings (PVRs) and strips (PVSs). BQ-123 (0.6, 1, and 6 microM) and PD-145065 (0.06, 0.1, 0.6, and 6 microM) were used to differentiate the subtypes because they are selective antagonists for ETA and nonselective antagonists for ETA-ETB receptors, respectively. To characterize the ET receptors further, sarafotoxin-S6c (a selective ETB-receptor agonist) and IRL-1038 (a selective ETB-receptor antagonist) were used. In PVRs, cumulative additions of ET-1 (0.1-100 nM) caused graded and slow contractions and potentiated spontaneous rhythmic contractions. The EC50 values and maximal response to 100 nM of ET-1 were 2.72 nM and 0.75 g, respectively (n = 7). PVSs showed ET-1 EC50 values very similar to those of PVRs, but Emax values to 100 nM of ET-1 were significantly lower (Emax = 0.33 g; n = 7). Moreover, ET-1 clearly increased the amplitude and frequency of spontaneous contractions in both types of specimens, although these were greater in the PVSs. Thirty-minute incubation with the selective ETA-receptor antagonist BQ-123 blunted ET-1-induced effects in PVS specimens but only weakly antagonized ET-1-induced contractions in PVRs. In contrast, the nonselective ETA-ETB-receptor antagonist PD-145065 significantly shifted the ET-1 concentration-response curve to the right in PVRs and partially inhibited ET-1 effects in PVSs. Moreover, sarafotoxin-S6c (0.1-100 nM) contracted PVRs and PVSs in a similar manner to ET-1; its effects were antagonized by IRL-1038 only at the PVR level. The differences observed in PVR and PVS specimens in response to agonists and antagonists of ET confirmed the great heterogeneity of endothelin-sarafotoxin receptors. In our experimental models, functionally ETB-like (or non-ETA) receptors seem mostly to mediate vasoconstriction.

Effects of enkephalins on bile-secreting function

Various doses of leu- and met-enkephalins injected into the portal vein of rats inhibited predominantly the secretory function of the liver. In most instances, the changes in bile secretion were observed to coincide in direction, time of occurrence, and magnitude with those in the secretion of bile acids.

Comparative study of elgodipine and nisoldipine on the contractile responses of various isolated blood vessels

The effects of elgodipine, a new dihydropyridine derivative, were compared to those of nisoldipine on contractile responses in various isolated artery rings and on mechanical activity in portal vein segments. Arteries used were: rabbit aorta, mesenteric (fifth branch), femoral and basilar, and sheep coronary arteries. Elgodipine and nisoldipine (10 −16−3 × 10 −6 M) produced a concentration-dependent inhibition of the contractile responses induced by high K + (80 mM), 5-hydroxytryptamine (10 −5 M) or noradrenaline (10 −6 M or 10 −4 M) in all the arteries studied. The inhibitory effect of elgodipine was greater in mesenteric resistance vessels (IC 50 = 8.0 ± 2.1 × 10 −12 M and 2.0 ± 0.5 × 10 −13 M for the depression of high K +- and agonist-induced contraction, respectively), and in coronary arteries (IC 50 = 2.6 ± 0.3 × 10 −10 M and 9.0 ± 1.4 × 10 −8 M for the inhibition of high K +-and agonist-induced contraction, respectively). In addition, the action of elgodipine in peripheral resistance vessels and in the coronary artery was more prominent than in aorta or femoral arteries, and this tissue selectivity was more apparent for elgodipine than for nisoldipine. In rat portal vein elgodipine (IC 50 = 6.5 ± 0.9 × 10 −8 M) and nisoldipine (IC 50 = 8.5 ± 1.3 × 10 −8 M) reduced in a concentration-dependent manner the development of mechanical activity. Furthermore, contractile responses produced by the addition of Ca 2+ (1–5 mM) to Ca 2+-free high K + solution were also concentration dependently inhibited by elgodipine. However, elgodipine did not modify noradrenaline-induced contractions attributed to intracellular Ca 2+ release. The results of this study indicate that elgodipine has potent vasodilator properties and vascular selectivity. The mechanisms through which elgodipine relaxes vascular smooth fibres seem to be related to its ability to inhibit the entry of extracellular Ca 2+ into the cell.

Length-tension dependence in vascular smooth muscle: possible participation of endothelin.

The results of experiments with isolated strips of rat portal vein, and of 'sandwich' experiments involving strips of the portal vein or aorta, revealed the involvement of endothelin in the development of myogenic reactions of the vascular smooth muscle, observed on distension of the vascular wall. Released by the endothelial cells, endothelin is capable of stimulating the contraction of these muscles.

A Gi1-2-protein is required for alpha 2A-adrenoceptor-induced stimulation of voltage-dependent Ca2+ channels in rat portal vein myocytes.

In rat portal vein myocytes, alpha 2A-adrenoceptors activate voltage-dependent Ca2+ channels via a transduction pathway requiring protein kinase C activation mediated by a pertussis-toxin-sensitive G-protein. As revealed by the use of antibodies directed against the different alpha-subunits expressed in portal vein myocytes, we show that the clonidine-induced stimulation of voltage-dependent Ca2+ channels is mainly mediated by a Gi1-2-protein.

4-(2-pyridyl)-2,2-dimethylnaphthalen-1-ones as new potassium channel activators with increased airways selectivity

A new series of 4-(2-pyridyl)-2,2-dimethylnaphthalen-1-one potassium channel activators has been prepared and their in vitro 1 relaxant activities in isolated rat portal vein and guinea-pig tracheal spirals as well as their hypotensive and bronchodilatory effects have been evaluated. Oxidation of the pyridyl nitrogen atom and a double bond between positions 3 and 4 provide compounds with some degree of airways selectivity.

Effects of BRL55834 in rat portal vein and bovine trachea: evidence for the induction of a glibenclamide‐resistant, ATP‐sensitive potassium current

1. The effects of the benzopyran K-channel opener, BRL55834, on mechanical activity in bovine trachealis and rat portal vein were studied together with membrane currents in freshly-isolated single cells derived from these tissues. 2. BRL55834 (3 nM-1 microM) produced a concentration-dependent relaxation of bovine trachealis precontracted with 100 microM histamine and reduced the spontaneous mechanical activity of rat portal veins, effects which were antagonized by glibenclamide (1-10 microM) but were not reversible on washing. In contrast, charybdotoxin (250 nM) did not modify the spasmolytic effect of BRL55834 in bovine trachealis. 3. BRL55834 (10 nM-10 microM) did not relax segments of bovine trachealis precontracted with 80 mM KCl. 4. In some freshly-isolated single cells from bovine trachealis held at -10 mV, BRL55834 (3 microM) induced a time-independent outward K-current which was partially resistant to inhibition by glibenclamide (10 microM). In other cells, a very noisy, outwardly-rectifying and charybdotoxin-sensitive current developed in the presence of BRL55834 (3 microM) and in time-matched control cells. 5. In freshly-isolated single cells from rat portal vein held at -10 mV, BRL55834 (3 microM) induced a time- and calcium-independent outward K-current which was partially resistant (approximately 25% inhibition at +40 mV) to subsequent inhibition by glibenclamide (10 microM). In contrast, levcromakalim induced a time-independent outward K-current which was completely inhibited by glibenclamide 10 microM. 6. With the non-hydrolysable ATP analogue, AMP-PCP (5 mM), in the pipette, the ability of BRL55834 to induce a time-independent K-current in portal vein cells was markedly reduced (approximately 80% inhibition at +40 mV) whereas the effects of 10 microM levcromakalim were totally inhibited. 7. The glibenclamide-resistant current component induced by BRL55834 was totally inhibited by phentolamine (100 microM), a concentration that had no effect on the peak current (IBK(Ca)) induced by NS1619 (33 microM). 8. Stationary fluctuation analysis of the noise associated with the glibenclamide-insensitive K-current induced by BRL55834 in rat portal vein cells indicated that the unitary current flowing through the underlying channels was 0.26 pA at -10 mV, a value inconsistent with the involvement of BKCa. 9. It is concluded that the relaxations of both bovine trachea and rat portal vein produced by BRL55834 are associated with the opening of K-channels. These are probably identical to the ATP-sensitive K-channel opened by levcromakalim, although the involvement of an additional K-channel cannot be excluded. The reduced sensitivity of the BRL55834-induced changes to glibenclamide and toAMP-PCP may result from avid binding of BRL55834 to its site of action.

The relaxant action of jatrophone in rat portal vein. A comparison with protein kinase C inhibitors

Jatrophone, staurosporine and H-7, caused graded inhibition of rat portal vein contractions induced by phorbol 12-myristate 13-acetate (PMA), noradrenaline, endothelin-1 or KCl, with IC 50s of 86 nM, 13 μM, 11 μM and 9 μM, respectively. Jatrophone was equipotent to H-7, but 100 to 500 fold less potent than staurosporine. Jatrophone, H-7 and staurosporine, also dose-dependently inhibited rhythmic contractions of the rat portal-mesenteric vein with IC 50s of 15 μM, 9 μM and 75 nM, respectively. Jatrophone, H-7 and staurosporine caused graded relaxations of preparations contracted with endothelin-1 or PMA with IC 50s of 12 and > 1000 μM, 8 and 13 μM and 7 and 12 nM, respectively. All three compounds caused graded inhibition of caffeine-induced contractions in Ca -free solution containing EGTA. The similarity between the vasorelaxant actions of Jatrophone, staurosporine and H-7 in rat portal vein suggests that Jatrophone acts, at least in part, through inhibition of PKC-dependent mechanisms. Moreover, like the PKC inhibitors, its vasorelaxant action may also involve other mechanisms unrelated to protein kinase C inhibition.