Endothelin action on vascular smooth muscle involves inositol trisphosphate and calcium mobilization

Insights into Endothelin Receptors in Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease which affects the cardiopulmonary system; it is defined as a mean pulmonary artery pressure (mPAP) > 20 mmHg as measured by right heart catheterization at rest, and is caused by complex and diverse mechanisms. In response to stimuli such as hypoxia and ischemia, the expression and synthesis of endothelin (ET) increase, leading to the activation of various signaling pathways downstream of it and producing effects such as the induction of abnormal vascular proliferation during the development of the disease. This paper reviews the regulation of endothelin receptors and their pathways in normal physiological processes and disease processes, and describes the mechanistic roles of ET receptor antagonists that are currently approved and used in clinical studies. Current clinical researches on ET are focused on the development of multi-target combinations and novel delivery methods to improve efficacy and patient compliance while reducing side effects. In this review, future research directions and trends of ET targets are described, including monotherapy and precision medicine.

EDNRA Gene rs1878406 Polymorphism is Associated With Susceptibility to Large Artery Atherosclerotic Stroke

Objective: We performed this study to investigate whether the EDNRA gene rs1878406 C > T polymorphism is associated with risk of large artery atherosclerosis (LAA) stroke in the Chinese Han population. Methods: Genotyping of rs1878406 was performed in 1,112 LAA stroke patients and 1,192 healthy controls. Multivariate logistic regression analyses were applied to assess the effect of the rs1878406 C > T polymorphism on susceptibility to LAA stroke. Results: A significant increase of LAA stroke risk was found in the recessive model (TT vs. CC/TC, OR = 1.74, 95% CI = 1.23-2.48, p = 0.002) and co-dominant model (TC vs. CC, OR = 1.06, 95% CI = 0.89-1.27, TT vs. CC, OR = 1.79, 95% CI = 1.25-2.55, p = 0.006). However, the interaction between age and genotypes of rs1878406 was not statistically significant, and no significant interactive effect was observed between the rs1878406 C > T polymorphism and sex (p > 0.05). Conclusion: The rs1878406 C > T polymorphism is associated with increased risk of LAA stroke in the Chinese Han population.

Calmodulin-dependent binding to the NHE1 cytosolic tail mediates activation of the Na+/H+ exchanger by Ca2+ and endothelin

The mammalian Na(+)/H(+) exchanger isoform 1 (NHE1) is a ubiquitous plasma membrane protein that regulates intracellular pH by removing a single proton (H(+)) in exchange for one extracellular Na(+). The human protein contains a ∼500-amino acid membrane domain and a regulatory, ∼315-amino acid cytosolic domain. NHE1 is activated by a number of hormones including endothelin (ET) and by Ca(2+). The regulatory tail possesses an inhibitory calmodulin (CaM)-binding domain, and inhibition of NHE1 is relieved by binding of a Ca(2+)-CaM complex. We examined the dynamics of ET-1 and Ca(2+) regulation of binding to NHE1 in vivo. CFP was linked to the NHE1 protein cytoplasmic COOH terminus. This was stably transfected into AP-1 cells that are devoid of their own NHE1 protein. The protein was expressed and targeted properly and retained NHE1 activity comparable to the wild-type protein. We examined the in vivo coupling of NHE1 to CaM by Förster resonance energy transfer using CaM linked to the fluorescent protein Venus. CaM interaction with NHE1 was dynamic. Removal of serum reduced CaM interaction with NHE1. Addition of the Ca(2+) ionophore ionomycin increased the interaction between CaM and NHE1. We expressed an ET receptor in AP-1 cells and also found a time-dependent association of NHE1 with CaM in vivo that was dependent on ET treatment. The results are the first demonstration of the in vivo association of NHE1 and CaM through ET-dependent signaling pathways.

Endothelin 1 stimulates Ca2+-sparks and oscillations in retinal arteriolar myocytes via IP3R and RyR-dependent Ca2+ release

PURPOSE

To investigate endothelin 1 (Et1)-dependent Ca(2+)-signaling at the cellular and subcellular levels in retinal arteriolar myocytes.

METHODS

Et1 responses were imaged from Fluo-4-loaded smooth muscle in isolated segments of rat retinal arteriole using confocal laser microscopy.

RESULTS

Basal [Ca(2+)](i), subcellular Ca(2+)-sparks, and cellular Ca(2+)-oscillations were all increased during exposure to Et1 (10 nM). Ca(2+)-spark frequency was also increased by 90% by 10 nM Et1. The increase in oscillation frequency was concentration dependent and was inhibited by the EtA receptor (Et(A)R) blocker BQ123 but not by the EtB receptor antagonist BQ788. Stimulation of Ca(2+)-oscillations by Et1 was inhibited by a phospholipase C blocker (U73122; 10 μM), two inhibitors of inositol 1,4,5-trisphosphate receptors (IP(3)Rs), xestospongin C (10 μM), 2-aminoethoxydiphenyl borate (100 μM), and tetracaine (100 μM), a blocker of ryanodine receptors (RyRs).

CONCLUSIONS

Et1 stimulates Ca(2+)-sparks and oscillations through Et(A)Rs. The underlying mechanism involves the activation of phospholipase C and both IP(3)Rs and RyRs, suggesting crosstalk between these Ca(2+)-release channels. These findings suggest that phasic Ca(2+)-oscillations play an important role in the smooth muscle response to Et1 within the retinal microvasculature and support an excitatory, proconstrictor role for Ca(2+)-sparks in these vessels.

Contractile Response of Human Omental Arteries to Endothelin

The effects of endothelin have been studied in isolated arterial segments (0·8–1 mm in external diam.) of human omental arteries obtained during the course of abdominal operations (15 patients, 7 men and 8 women). Paired segments, one normal and the other de-endothelized, were mounted for isometric recording of tension in organ baths. Endothelin produced concentration-dependent contractions with an EC50 value of 5·4 × 10−9  m. Removal of endothelium did not affect significantly endothelin-induced contractions (EC50, 6·7 × 10−9  m). Removal of extracellular calcium or addition of the calcium channel blocker nicardipine (10−6  m) diminished but did not abolish responses to endothelin. These results indicate that endothelin exerts powerful contractile effects on human isolated omental arteries which are independent of the presence of an intact endothelial cell layer; this contraction cannot be explained solely by voltage-dependent calcium channels.

Contractile changes of the clitoral cavernous smooth muscle in female rabbits with experimentally induced overactive bladder

INTRODUCTION

Recently, growing clinical evidence has suggested that sexual dysfunction is more prevalent in women with overactive bladder (OAB). Aims. However, there has been no basic research to clarify the relationship between OAB and female sexual dysfunction. Therefore, we investigated this issue using a rabbit model of OAB.

METHODS

Twenty-seven New Zealand white female rabbits were randomly divided into the OAB and control groups.

MAIN OUTCOME MEASURES

The contractile responses of clitoral cavernous strips to K(+), phenylephrine (PE), Bay K 8644, and endothelin (ET)-1, and the relaxation responses of acetylcholine (ACh), sodium nitroprusside (SNP), and Y-27632 to PE-induced contraction by measuring isometric tension. Results. The contractile responses to K(+), PE, Bay K 8644, and ET-1 were significantly more increased in the OAB group in a dose-dependant manner than in the control group (P < 0.05), and the responses to ET-1 were more prominent than those to the remaining substances (P < 0.01). The increased contractile responses to ET-1 were blocked by BQ123 (ET(A) receptor antagonist) but not by BQ788 (ET(B) receptor antagonist). Clitoral cavernosal strips from the OAB group were more difficult to relax than those from the control group in terms of ACh- and SNP-induced relaxation (P < 0.05). The Y-27632-induced relaxant responses to PE- and ET-1-induced contraction were less prominent in the OAB group than in the control group. CONCLUSIONS; The results of this study provide evidence that female OAB may deteriorate clitoral engorgement, which is associated with a greater force generation by increased calcium sensitization and subsequently decreased of relaxation. The activation of ET and Rho-kinase system may be crucial to negatively effect the clitoral smooth muscle relaxation in experimentally induced OAB animal model. But whether these vasomotor effects are revived in human clitoris is still debatable.

Endothelin-1 increases intracellular Ca(2+) in rabbit pulmonary artery smooth muscle cells through phospholipase C

In freshly isolated rabbit pulmonary artery smooth muscle cells, endothelin (ET)-1 induced a transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) followed by a return to the initial [Ca(2+)](i). This response was not abolished by the voltage-dependent Ca(2+) channel blocker nicardipine or removal of Ca(2+) from the bath solution but was inhibited by ryanodine and thapsigargin. This finding suggested that the increase in [Ca(2+)](i) induced by ET-1 was attributable to release of Ca(2+) from ryanodine- and inositol 1,4,5-trisphosphate-sensitive intracellular Ca(2+) stores. The transient increase in [Ca(2+)](i) induced by ET-1 was also inhibited by pretreatment with antagonists of ET type A and B (ET(A) and ET(B)) receptors (BQ-123 and BQ-788, respectively). Furthermore, the ET(B) receptor agonist IRL-1620 induced an increase in [Ca(2+)](i) that was followed by a sustained increase in [Ca(2+)](i); the sustained increase in [Ca(2+)](i) was blocked by nicardipine. Using the nystatin-perforated patch-clamp technique, we found that IRL-1620 caused an increase in Ca(2+) current that was inhibited by addition of ET-1. ET-1 did not inhibit Ca(2+) current when cells were pretreated with BQ-123. These results suggested that when both receptor types are activated, the opposing responses lead to abolition of the sustained [Ca(2+)](i) increases induced by ET(B) receptor activation. Western blot analysis confirmed expression of ET(A) and ET(B) receptors. Finally, U-73122 inhibited the ET-1-induced [Ca(2+)](i) increase, indicating that phospholipase C was involved in modulation of the ET-1-induced [Ca(2+)](i) increase in rabbit pulmonary artery smooth muscle cells.

Endothelin-1 acts via protein kinase C to block KATP channels in rabbit coronary and pulmonary arterial smooth muscle cells

We investigated the effects of the vasoconstrictor endothelin-1 (ET-1) on the whole-cell ATP-sensitive K+ (KATP) currents of smooth muscle cells that were isolated enzymatically from rabbit coronary artery (CASMCs) and pulmonary artery (PASMCs). The size of the KATP current did not differ significantly between CASMCs and PASMCs. ET-1 reduced the KATP current in a concentration-dependent manner, and this inhibition was greater in PASMCs than in CASMCs (half-inhibition values of 12.20 nM and 1.98 nM in CASMCs and PASMCs, respectively). However, the level of inhibition induced by other vasoconstrictors (angiotensin II, norepinephrine, and serotonin) were not significantly different between CASMCs and PASMCs. Pretreatment with the protein kinase C (PKC) inhibitors staurosporine (100 nM) and GF 109203X (1 microM) prevented ET-1-induced inhibition of the KATP current in both arterial smooth muscle cell preparations. The PKC activators phorbol-12,13-dibutyrate (PDBu) and 1-olelyl-2-acetyl-sn-glycerol (OAG) reduced the KATP current in dose-dependent manner. Although the numbers of ET receptors were not significantly different between the 2 arterial smooth muscle cell preparations, the effects of PDBu and OAG were greater on PASMCs. ET-1-induced inhibition of the KATP current was unaffected by the PKA inhibitor Rp-cAMPs (100 microM) and PKA inhibitory peptide (5 microM).

Endothelin and erectile dysfunction: a target for pharmacological intervention?

Although erectile dysfunction (ED) is not life threatening, this common problem can significantly affect the quality of life and psychological and social well-being. The Massachusetts male ageing study (1,290 men aged 40 - 70 years) showed that 52% of men reported some degree of ED (17.1% mild, 25.2% moderate, 9.6% total). In the UK, an estimated 17 - 19% of men are thought to suffer from ED. This problem is more common with advancing age and since this proportion of the population is increasing, the prevalence of ED is expected to rise. Endothelin-1 (ET-1) belongs to a family of potent vasoconstrictor peptides consisting of 21 amino acids. We review the evidence showing that ET-1 plays a role via (ET(A) and ET(B) receptors) in the regulation of cavernosal smooth muscle tone. We also consider the various risk factors that are involved in the pathogenesis of ED and how these relate to the action of ET-1. In particular, the role of diabetes, hypertension, smoking and dyslipidaemia are discussed. The pharmaceutical industry has declared an interest in the development of ET antagonists for use in the treatment of various diseases including ED. We briefly comment on experimental ET-1 antagonists that may be of therapeutic benefit in ED.

Inhibition of endothelin-1 and KCL-induced increase of [CA2+]i by antiglaucoma drugs in cultured A7r5 vascular smooth-muscle cells

Over contraction of vascular smooth muscle may result in ischemia to ocular neuronal cells and deteriorate the glaucoma. The purpose of this study was to investigate the inhibitory effects of various commercial antiglaucoma drugs including brimonidine, dipivefrin, betaxolol, timolol, levobunolol, carteolol, brinzolamide, dorzolamide, unoprostone, latanoprost, pilocarpine, and preservative benzalkonium chloride on endothelin-1(ET-1) and KCl-induced increase of intracellular free Ca2+ ([Ca2+]i) in cultured rat A7r5 vascular smooth muscle cells. These drugs were diluted from original concentrations to 1/100, 1/1000, and 1/10000. [Ca2+]i mobility was analyzed by spectrofluorometry after loading with fura-2-AM. Betaxolol, timolol, levobunolol, and carteolol were found to inhibit KCl-induced release of [Ca2+]i in a dose-dependent manner. High concentrations of betaxolol, timolol, levobunolol, carteolol, and unoprostone also inhibited ET-1-induced increase of [Ca2+]i in A7r5 cells. However, ET-1- and KCl-induced increase of [Ca2+]i was not diminished by other drugs including brimonidine, dipivefrin, brinzolamide, dorzolamide, latanoprost, pilocarpine, and benzalkonium chloride. These results indicate that high concentrations of unoprostone and beta-adrenergic blocking agents including betaxolol, timolol, levobunolol, and carteolol may inhibit ET-1-induced increase of [Ca2+]i. The mechanism may be mediated by inhibition of extracellular calcium influx via blocking of L-type voltage-dependent Ca2+ channel in A7r5 cells.

Eyeing endothelins: a cellular perspective

Endothelin is an endogenous vasoactive peptide that is considered among the most potent vasoconstrictor substances known. In addition to its vascular effects, endothelins and their receptors have been shown to be present in the eye and to have a number of ocular actions that may be important for ocular homeostasis, but, in excess can be a potential contributor to ocular neuropathy in glaucoma. The current review focuses on the cellular and molecular aspects of endothelins and its receptors in the eye with an emphasis on its relationship to ocular function and its potential role in the etiology of glaucoma pathophysiology.

ET-1-associated vasomotion and vasospasm in lymphatic vessels of the guinea-pig mesentery

In vitro experiments were performed to investigate the actions of endothelin-1 (ET-1) on vasomotion and vasospasm in guinea-pig mesenteric lymphatics. ET-1 modulated lymphatic vasomotion independent of the endothelium, with lower concentrations (<or=10 nm) increasing lymphatic vasomotion and higher concentrations (>or=100 nm) causing vasospasm. ET-1-induced increases in vasomotion were accompanied by an increase in tonic [Ca2+]i. These actions were inhibited by the ETA receptor antagonist BQ-123 (1 microm), the phospholipase C (PLC) inhibitor U73122 (5 microm), removal of extracellular Ca2+, chelation of intracellular Ca2+ with BAPTA/AM (10 microm), the store Ca2+-ATPase inhibitor thapsigargin (1 microm), caffeine (10 mm) and the inositol 1,4,5-trisphosphate (IP3) receptor blocker heparin and 2-APB (30 microm). In contrast, the ETB receptor antagonist BQ-788 (1 microm), ryanodine (1 & 20 microm), pertussis toxin (PTx) or Cs+ had no significant actions on vasomotion or the magnitude of increase in tonic [Ca2+]i. ET-1-induced vasospasm was accompanied by a transient increase in smooth muscle [Ca2+]i followed by a sustained plateau, an action that was abolished by removal of extracellular Ca2+, but only marginally inhibited by nifedipine (1 microm). Caffeine (10 mm), SKF 96165 (30 microm) or U73122 (5 microm) together with nifedipine (1 microm) abolished ET-1-induced vasospasm and increase in [Ca2+]i. These results indicate that ET-1 increases lymphatic vasomotion by acting on smooth muscle ETA receptors and activation of G-protein-PLC-IP3 cascade, which is known to cause pacemaker Ca2+ release and resultant pacemaker potentials. High concentrations of ET-1 cause a failure in Ca2+ homeostasis causing vasospasm, triggered by excessive Ca2+ influx primarily through store-operated channels (SOCs) with l-Ca2+ voltage-operated channels (VOCs) also contributing, but to a much lesser extent.

Effects of commercial antiglaucoma drugs to glutamate-induced [Ca2+)]i increase in cultured neuroblastoma cells

Over releasing of glutamate and cellular calcium influx always results in neuronal death. In the present study, we investigated various commercial antiglaucoma drugs including timolol (0.58 microM to 58 microM), betaxolol (1.62 microM to 162 microM), carteolol (6.8 microM to 680 microM), pilocarpine (4.08 microM to 408 microM), latanoprost (0.01 microM to 1.1 microM), dorzolamide (6.16 microM to 616 microM), brinzolamide (2.6 microM to 260 microM), brimonidine (0.68 microM to 68 microM), dipivefrin (0.28 microM to 28 microM) and preservative benzalkonium chloride on their effects to inhibit glutamate-induced intracellular free Ca(2+) ([Ca(2+)](i)) increase in cultured N1E-115 neuroblastoma cells. These drugs were diluted from original concentrations to 1/100, 1/1000 and 1/10000. The [Ca(2+)](i) mobility was studied after loading with fura-2-AM and analyzed by spectrofluorometry. It was found that betaxolol, dipivefrin and brimonidine have remarkable effects not only to inhibit the glutamate-induced [Ca(2+)](i) increase but also to decrease the basal [Ca(2+)](i). In the case of other drugs, only high concentration of timolol (58 microM) exhibited significant effect to completely prevent glutamate-induced [Ca(2+)](i) increase. Moreover, benzalkonium chloride did not exhibit any inhibitive effect. These results indicate that betaxolol, dipivefrin and brimonidine may have neuroprotective effects to inhibit the glutamate-induced over Ca(2+) influx damage.

Change of cytosolic Ca(2+) mobility in cultured bovine corneal endothelial cells by endothelin-1

The effect of endothelin-1 (ET-1) on the intracellular free Ca(2+) ([Ca(2+)](i)) in cultured bovine corneal endothelial cells was studied after loading with fura-2-AM. In Ca(2+)-containing buffer and Ca(2+)-free buffer, ET-1 induced a significant rise in [Ca(2+)](i) at concentrations from 10(-9) to 10(-7) M. In Ca(2+)-free buffer, pretreatment of the cells with ET-1 inhibited thapsigargin-induced [Ca(2+)](i) increase and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced Ca(2+) release by 99% and 62%, respectively. Pretreatment of the cells with thapsigargin or CCCP also inhibited ET-1-induced [Ca(2+)](i) rise by 36% and 92%, respectively. In Ca(2+)-containing buffer, the ET(A) receptor antagonist (BQ123) and ET(B) receptor antagonist (BQ788) partially inhibited ET-1-induced [Ca(2+)](i) by 92% and 98%, respectively. Nifedipine and La(3+) also inhibited ET-1-induced [Ca(2+)](i) increase by 26% and 91%, respectively. The intracellular calcium release caused by ET-1 was partially inhibited by phospholipase C inhibitor (U73122). After incubation of the cells with ET-1 in Ca(2+)-free buffer, the addition of 5 mM CaCl(2) increased Ca(2+) influx, implying that release of Ca(2+) from internal stores caused by ET-1 further induced capacitative Ca(2+) entry. These data suggest that ET-1-induced [Ca(2+)](i) rise in bovine corneal endothelial cells are mediated by ET(A) receptor, ET(B) receptor, La(3+)-sensitive Ca(2+) pump and L-type voltage-operated Ca(2+) channel, leading to Ca(2+) influx. ET-1 also increased the internal Ca(2+) release from endoplasmic reticulum and mitochondria Ca(2+) stores followed by capacitative Ca(2+) entry. ET-1-induced intracellular Ca(2+) release was modulated by phospholipase C-coupled events.

Endothelin-1 stimulated capacitative Ca2+ entry through ET(A) receptors of a rat brain-derived type-1 astrocyte cell line, IA-1g1

The present study demonstrated that endotheline-1 (ET-1) stimulated a biphasic (transient and sustained) increase in [Ca(2+)](i) and signaling was blocked by BQ123 and inhibited by BQ788. RT-PCR analysis revealed that ET(A) was expressed more than ET(B) mRNA-suggesting that ET(A) is the major receptor. Simply reintroducing Ca(2+) in the buffer stimulated a sustained increase in [Ca(2+)](i) and the effect was inhibited by U73122, thapsigargin (TG), miconazole and SKF96365. When measured in Ca(2+)-free buffer, the ET-1-stimulated Ca(2+) transient decreased by 73% and the reintroduction of Ca(2+) induced a large sustained increase in [Ca(2+)](i). These effects were not affected by nifedipine, but were inhibited by miconazole and SKF96365-indicating that the sustained increase in [Ca(2+)](i) mediated by ET-1 was mostly due to capacitative Ca(2+) entry (CCE). The ET-1-induced CCE was inhibited by phorbol ester (PMA) but was enhanced by GF109203X; it was also enhanced by 8-bromo-cyclic AMP (8-Br-cAMP) but was inhibited by H89. Thus, protein kinase C (PKC) negatively regulated and cAMP-dependent protein kinase (PKA) positively regulated the ET-1-mediated CCE in these cells.

Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: effect on platelet aggregation and coagulation

Endothelial-derived proteoglycans are important regulators of the coagulation-pathway in vivo and our primary objective of this study was to determine whether chronic shear stress affected the synthesis, release, and activity of proteoglycans from bovine aortic endothelial cells (BAEC). BAEC were cultured under shear and proteoglycans were purified from BAEC conditioned media and analyzed using both anionic exchange and size exclusion chromatography. The overall amount of proteoglycans produced per cell was significantly greater for the high shear-treated samples compared to the low shear-treated samples indicating that the shear magnitude did impact cell responsiveness. While overall size and composition of the proteoglycans and glycosaminoglycan (GAG) side chains were not altered by shear, the relative proportion of the high and low molecular weight species was inversely related to shear and differed significantly from that found under static tissue culture conditions. Moreover, a unique proteoglycan peak was identified from low shear stress (5 +/- 2 dynes/cm(2)) conditioned media when compared to high shear conditions (23 +/- 8 dynes/cm(2)) via anionic exchange chromatography, suggesting that subtle changes in the GAG structures may impact activity of these molecules. In order to characterize whether these changes impacted proteoglycan function, we studied the effects of shear specific proteoglycans on the inhibition of thrombin-induced human platelet aggregation as well as on platelet-fibrin clot dynamics. Proteoglycans from high shear-treated samples were less effective inhibitors of both platelet aggregation and blood coagulation inhibition than proteoglycans from low shear-treated samples and both were less effective than proteoglycans isolated from static tissue culture samples. However, due to changes in the overall proteoglycan synthesis and release rate, the high and low shear-treated sample had essentially identical effects on these activities, suggesting that the cells were able to compensate for stress-induced proteoglycan changes. Our data suggests that shear stress, by altering proteoglycan synthesis and fine structure, may play a role in maintaining vascular hemodynamics and hemostasis.

Comparison of endothelin-1-mediated tissue tension and calcium mobilization effects in isolated rabbit corpus cavernosum

OBJECTIVES

To directly compare and contrast the effects of endothelin-1 (ET-1) and adrenoreceptor agonists norepinephrine and phenylephrine on eliciting calcium influx in primary rabbit corpus cavernosum cells and their ability to elicit tissue contractions. The potent vasoconstrictor peptide ET-1 and the alpha-adrenoreceptor agonists are important modulators of smooth muscle tone in the penile corpus cavernosum. However, the mechanisms involved in maintaining smooth muscle tone and contraction are not clearly understood.

METHODS

Intracellular calcium mobilization was measured in cultured corpus cavernosum smooth muscle cells using calcium-sensing dyes in conjunction with a fluorometric imaging plate reader. Tissue tension studies on rabbit corpus cavernosum were conducted using organ chambers.

RESULTS

ET-1 at concentrations as low as 10 nM was sufficient to induce a transient increase of intracellular calcium in these cells. In contrast, concentrations of 1 mM and greater of norepinephrine and phenylephrine were required to elicit comparable calcium fluxes in cavernosum cells. Tissue bath studies indicated that ET-1 is a potent stimulator of corpus cavernosum smooth muscle contraction, with concentrations as low as 10 nM sufficient to initiate contraction.

CONCLUSIONS

The potency of ET-1 in producing contraction on tissue strips and inducing calcium flux suggests that ET-1 might be an important mediator for modulating and maintaining corpus cavernosum smooth muscle tone. Therefore, additional exploration of the role of endothelins and their receptors in the tumescence and detumescence states of the penis would be extremely valuable.

Mechanism of endothelin-1-induced cytosolic Ca(2+) mobility in cultured H9c2 myocardiac ventricular cells

The effect of endothelin-1 (ET-1) on the intracellular free Ca(2+) ([Ca(2+)](i)) mobility in cultured H9c2 myocardiac ventricular cells was studied after loading with fura-2-AM. In Ca(2+)-containing buffer, ET-1 induced [Ca(2+)](i) rise from 10(-7) to 10(-9) M. ET-1 induced [Ca(2+)](i), which was composed of a first small peak and a secondary persistent plateau. In Ca(2+)-free buffer, pretreatment with 10(-7) M ET-1 inhibited the thapsigargin and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced [Ca(2+)](i) increase. Meanwhile, pretreatment with thapsigargin and CCCP also inhibited ET-1-induced [Ca(2+)](i) rise. In Ca(2+)-containing buffer, the ET(A) receptor antagonist (BQ123) completely abolished the secondary rising peak and plateau. Conversely, the ET(B) receptor antagonist (BQ788) completely inhibited the first small peak and secondary peak plateau. Nifedipine and La(3+) also abolished the 10(-7) M ET-1-induced [Ca(2+)](i) in the first rising peak. The internal Ca(2+) release induced by ET-1 was inhibited by U73122 (phospholipase C inhibitor), propranolol (phospholipase D inhibitor) and aristolochic acid (phospholipase A2 inhibitor). After incubation of 10(-7) M ET-1 in Ca(2+)-free buffer, the addition of 5 mM CaCl(2) increased Ca(2+) influx, implying that release of Ca(2+) from internal stores further induces capacitative Ca(2+) entry. Taken together, these results suggest that both ET(A) and ET(B) receptors are involved in ET-1-induced [Ca(2+)](i) rise in H9c2 myocardiac ventricular cells. Whereas ET(B) receptor seems to mediate the initial Ca(2+) influx via L-type Ca(2+) channel, ET(A) receptor appears to be involved in the subsequent Ca(2+) release from endoplasmic reticulum and mitochondria Ca(2+) stores.

Ca2+ mobilization in saphenous vein smooth muscle cells derived from patients with primary varicosity

BACKGROUND

Human primary varicosity is associated with 'weakness' of the vein wall. We investigated whether the reduced responsiveness of varicose veins to physiological vasoconstrictors might result from impaired Ca2+ mobilization in venous smooth muscle.

MATERIALS AND METHODS

The hypothesis was tested in cells derived from phenotypically different vein segments that were obtained from the inguinal saphenous vein (tissue with incompetent valves), the distal portion of the long saphenous vein just above the medial ankle (clinically healthy tissue), and from a tributary to the long saphenous vein just below the knee (incompetent and overtly varicose tissue). Saphenous vein from patients undergoing cardiac surgery served as control. Cytosolic free Ca2+ levels ([Ca2+]i) were determined with the fura-2 method in cultured medial smooth muscle cells of third to sixth passage (21-23 measurements per tissue derived from five controls and seven patients).

RESULTS

Angiotensin II (10 nmol L-1 to 10 mumol L-1) induced a significantly (P < 0.05) smaller rise in [Ca(2+)1i response in cells derived from incompetent or varicose segments (approximatley 70 nmol L-1) than in cells derived from clinically healthy vein (approximately 130 nmol L-1) or controls (approximately 170 nmol L-1). Likewise, the effect of endothelin-1 (100 nmol L-1) on [Ca2+]i was considerably less in cells derived from segments with incompetent valves or from varicose vessel segments than in cells derived from control patients (P < 0.05). In organ baths, endothelium-denuded strips of varicose vessels contracted significantly less in response to these agonists than clinically healthy segments from the same patient.

CONCLUSIONS

The reduced contractility of diseased human varicose veins in response to angiotensin II and endothelin-1 involves impaired Ca2+ mobilization.

Effects of docosahexaenoic acid on calcium pathway in adult rat cardiomyocytes

In this study we examined the effect of polyunsaturated fatty acids (PUFAs), in particular of docosahexaenoic acid (DHA), on calcium homeostasis in isolated adult rat cardiomyocytes exposed to KCl, ET-1 and anoxia. Free [Ca(2+)](i) in rat cardiomyocytes was 135.7 +/- 0.5 nM. Exposure to 50 mM KCl or 100 nM ET-1 resulted in a rise in free [Ca(2+)](i) in freshly isolated cells (465.4 +/- 15.6 nM and 311.3 +/- 12.6 nM, respectively) and in cultured cells (450.8 +/- 14.8 nM and 323.5 +/- 14.8 nM respectively). An acute treatment (20 minutes) with 10 microM DHA significantly reduced the KCl- and ET-1-induced [Ca(2+)](i) increase (300.9 +/- 18.1 nM and 232.08 +/- 11.8 nM, respectively). This reduction was greater after chronic treatment with DHA (72 h; 257.7 +/- 13.08 nM and 192.18 +/- 9.8 nM, respectively). Rat cardiomyocytes exposed to a 20 minute superfusion with anoxic solution, obtained by replacing O(2) with N(2) in gas mixture, showed a massive increase in cytosolic calcium (1200.2 +/- 50.2 nM). Longer exposure to anoxia induced hypercontraction and later death of rat cardiomyocytes. Preincubation with DHA reduced the anoxic effect on [Ca(2+)](i) (498.4 +/- 7.3 nM in acute and 200.2 +/- 12.2 nM in chronic treatment). In anoxic conditions 50 mM KCl and 100 nM ET-1 produced extreme and unmeasurable increases of [Ca(2+)](i.) Preincubation for 20 minutes with DHA reduced this phenomenon (856.1 +/- 20.3 nM and 782.3 +/- 7.6 nM, respectively). This reduction is more evident after a chronic treatment with DHA (257.7 +/- 10.6 nM and 232.2 +/- 12.5 nM, respectively). We conclude that in rat cardiomyocytes KCl, ET-1 and anoxia interfered with intracellular calcium concentrations by either modifying calcium levels or impairing calcium homeostasis. Acute, and especially chronic, DHA administration markedly reduced the damage induced by calcium overload in those cells.

Endothelin Induces a Rise of Inositol 1,4,5-Trisphosphate, Inositol 1,3,4,5-Tetrakisphosphate Levels and of Cytosolic Ca2+ Activity in Neural Cell Lines

The mechanism of action of the vasoconstricting peptide endothelin was investigated in two neural cell lines. In rat glioma cells endothelin-1 caused a biphasic rise in cytosolic Ca2+ activity. A large peak of 40 s duration was followed by another, however smaller, transient rise of comparable duration. In the absence of extracellular Ca2+ only the first peak was detected. Pretreatment with Ca2+ ionophores suppressed the Ca2+ response to endothelin. At the concentrations used the Ca2+ ionophores primarily deplete internal Ca2+ stores and prevent their refilling. Measurements of 45Ca2+ fluxes corroborate the conclusion that in the glioma cells endothelin induces firstly a release of Ca2+ from internal stores and subsequently a stimulation of Ca2+ entry. In neuronal cells (mouse neuroblastoma x rat glioma hybrid cells), endothelin caused a monophasic rise in cytosolic Ca2+ activity, most likely due to release from internal stores. In the glioma cells the concentrations of both inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate were raised about 2.5-fold for ca. 90 s after addition of endothelin. In the neuronal cells a shorter, smaller rise in inositololigophosphate concentrations was induced. Thus, endothelin seems to act as a neuropeptide activating phospholipase C and intracellular Ca2+.

Endothelin-evoked Release of Arachidonic Acid from Mouse Astrocytes in Primary Culture

In striatal astrocytes, receptors for the vasoactive peptide endothelin (ET) are associated with several intracellular signalling pathways: ET-1 increases the breakdown of phosphoinositides, induces a sustained influx of Ca2+ and inhibits the isoproterenol-induced formation of cAMP (Marin et al., J. Neurochem., 56, 1270 - 1275, 1991). In the present study, it will be shown that ET-1 and ET-3 markedly stimulate the release of arachidonic acid (AA) from cultured astrocytes from the mouse striatum (EC50=3 and 7 nM for ET-1 and ET-3, respectively), mesencephalon and cerebral cortex. The ET-1-evoked release of AA probably resulted from the activation of a phospholipase A2, since it required extracellular Ca2+ and was prevented by mepacrine but not by RHC 80267, an inhibitor of diacylglycerol lipase. The ET-1-induced release of AA was shown to be partially mediated by a guanine nucleotide-binding protein sensitive to pertussis toxin but not to cholera toxin. A cAMP-dependent process is not involved since the ET-1-evoked release of AA was not affected when cells were incubated with either isoproterenol or 8-bromo-cAMP. The ET-1-evoked release of AA could be mimicked by the co-application of a calcium ionophore and a protein kinase C activator. However, staurosporine, a potent inhibitor of protein kinase C, which blocked the release of AA induced by the combined application of ionomycin and phorbol 12-myristate 12-acetate (PMA), was without effect on the ET-1-evoked response, indicating that protein kinase C is not directly involved in the ET-1-induced release of AA. Furthermore, the responses induced by ET-1 and by PMA were found to be additive. These results suggest that (1) ET-1 receptors are coupled to the release of AA by a mechanism independent of both protein kinase C activation and the adenylate cyclase pathway, possibly via the activation of phospholipase A2, (2) different mechanisms (or different phospholipase A2 subtypes) are involved in the control of AA release in astrocytes.

Endothelin receptor blockers reduce I/R-induced intestinal mucosal injury: role of blood flow

The aim of the present study was to assess the role of endothelin (ET) in ischemia-reperfusion (I/R)-induced mucosal injury. Mucosal permeability ((51)Cr-EDTA clearance) and tissue myeloperoxidase (MPO) activity were significantly increased after 30 min of ischemia followed by 30 min of reperfusion. The I/R-induced increases in mucosal permeability and polymorphonuclear leukocyte (PMN) infiltration were significantly attenuated by pretreatments with ET(A) (BQ-485) and/or ET(B) (BQ-788) receptor antagonists. Monoclonal antibody (MAb) directed against intercellular adhesion molecule-1 (ICAM-1; MAb 1A29) and superoxide dismutase (SOD) pretreatments significantly attenuated the increased mucosal permeability and PMN infiltration in a similar manner as with ET receptor antagonists. Superior mesenteric artery blood flow was significantly reduced during the reperfusion period. Both ET receptor antagonists caused a significant rise in blood flow compared with an untreated I/R group. In conclusion, our data suggest that ET(A) and/or ET(B) receptors, ICAM-1, and superoxide play an important role in I/R-induced mucosal dysfunction and PMN infiltration. Furthermore, ET is involved in the pathogenesis of post-reperfusion-induced damage and beneficial effects of ET receptor antagonism are related to an improvement of disturbed blood flow during the reperfusion period.

Stimulation of catecholamine biosynthesis via the protein kinase C pathway by endothelin-1 in PC12 rat pheochromocytoma cells

It has been reported that endothelins (ETs) stimulate catecholamine release from chromaffin cells. However, it is not known whether ETs also affect catecholamine biosynthesis. Thus, using a rat pheochromocytoma cell line, PC12, we examined the effects of ETs on catecholamine biosynthesis. The mRNA level and activity of tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine biosynthesis, were increased significantly by endothelin-1 (ET-1) (100nM). These stimulatory effects were inhibited completely by a blocker for the A-type endothelin receptor, BQ-123 [cyclo(D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl)] (1 microM), but not by a blocker for the B-type endothelin receptor, BQ-788 (N-cis 2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine (1 microM). Also, Ro-32-0432 (3-[8-[(dimethylamino)methyl]-6,7,8,9-tetrahydropyrido-[1,2-a]indol-10-yl]-4-(1-methyl-3-indolyl)-H-pyrrole-2,5-dione hydrochloride) (100nM), a protein kinase C inhibitor, completely inhibited ET-1-induced increases in TH activity and mRNA level. Furthermore, ET-1 (100nM) significantly stimulated protein kinase C activity, as well as inositol 1,4,5-triphosphate production; these stimulatory effects were abolished by BQ-123 but not by BQ-788. Moreover, ET-1 (100nM) significantly increased both the TH-protein level and the intracellular catecholamine content. By contrast to ET-1, endothelin-3 did not affect catecholamine synthesis. These results indicate that ET-1, but not ET-3, stimulates catecholamine synthesis through the PKC pathway in PC12 cells. Also, the use of selective ET receptor antagonists suggests that the effects of ET-1 on catecholamine biosynthesis are mediated through ET(A).

Cell-to-cell communication via nitric oxide modulation of oscillatory Cl(-) currents in rat intact cerebral arterioles

1. Diffusion-mediated changes in ion channel function within blood vessels have not been demonstrated directly in a patch-clamp study. Here, we examined the hypothesis that endothelium-derived diffusible bioactive substances would modify endothelin-1 (ET-1)-evoked membrane currents in smooth muscle cells situated within intact arterioles. 2. In pieces of arterioles dissected from the rat cerebral pial membrane, patch electrodes were placed on single smooth muscle cells identified under the microscope. Under perforated patch-clamp conditions, ET-1 evoked an oscillatory inward current at negative potentials in such cells in the presence of the gap junction disrupter 18alpha-glycyrrhetinic acid. ET-1 also elicited an oscillation superimposed on a membrane depolarization in current-clamp mode. 3. The oscillatory current exhibited an outwardly rectifying current-voltage relationship, a sensitivity to niflumic acid, a requirement for inositol 1,4,5-trisphosphate (IP(3))- and caffeine-sensitive Ca(2+) stores and for external Ca(2+) and a rank order of anion permeabilities characteristic of Ca(2+)-activated Cl(-) currents (I(Ca(Cl))). 4. This oscillatory response was inhibited by bradykinin (an effect distinct from the electrical propagation of hyperpolarization) and this effect was attenuated by the NO-synthase inhibitor N(omega)-nitro-L-arginine and by the NO scavenger oxyhaemoglobin but not by the cyclo-oxygenease inhibitor indomethacin. 8-Bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) and nitroprusside closely mimicked the effect of bradykinin. 5. The present patch-clamp study has revealed diffusion-mediated cell-to-cell interaction in an intact blood vessel: bradykinin appears to cause NO to move from endothelium to smooth muscle, there to inhibit an ET-1-evoked oscillatory I(Ca(Cl)) via the NO-cGMP pathway.

Exposure of endothelial cells to recombinant human erythropoietin induces nitric oxide synthase activity

BACKGROUND

Anemic patients with chronic renal failure receiving recombinant human erythropoietin (rHuEPO) therapy frequently develop hypertension through an unknown mechanism. We hypothesize that EPO receptors (EPORs) on endothelial cells (ECs) in various sites of vasculature may mediate the activities of nitric oxide synthase (NOS) and/or the release of endothelin-1 (ET-1), contributing to blood pressure changes. We tested this hypothesis using primary cultures of ECs obtained from human coronary artery (HCAEC), pulmonary artery (HPAEC), dermis (HDEC), and umbilical vein (HUVEC).

METHODS

EPORs were measured by 125I-EPO binding. The effect of EPO on EPOR, ET-1, and NOS mRNA levels was assessed by quantitative reverse transcription-polymerase chain reaction. Cellular NOS activity and ET-1 release into the medium was measured by the NOSdetect assay and by radioimmunoassay kits.

RESULTS

Short-term (4 h) treatment with EPO (4 U/mL) did not change the number or affinity of EPOR per cell. Neither were there any changes in the amount of EPOR, ET-1, and NOS transcripts (cDNA/microg of mRNA) nor in ET-1 release and NOS activity. In HUVEC only, 24-hour exposure to EPO caused a threefold increase in NOS transcript. In other cells, EPO treatment for six days increased NOS activity by twofold to fourfold.

CONCLUSIONS

We show that upon extended exposure, EPO induces NOS activity but does not affect ET-1 release. These findings indicate that the hypertensive effect of EPO is not likely to be caused by a direct effect on ECs.

Regional modulation of cyclic nucleotides by endothelin-1 in rat pulmonary arteries: direct activation of G(i)2-protein in the main pulmonary artery

The ability of endothelin-1 (ET-1) to modulate the cyclic nucleotides, guanosine 3' 5' cyclic monophosphate (cyclic GMP) and adenosine 3' 5' cyclic monophosphate (cyclic AMP) was assessed in the main elastic pulmonary elastic artery (4 - 5 mm i.d.) and the small muscular pulmonary arteries (150 - 200 micrometer i.d.) of the rat. ET-1 caused an increase in cyclic GMP in the larger vessels but had no effect in the smaller arteries. The increase in cyclic GMP was not dependent on an intact endothelium and was inhibited by the ET(A)-receptor antagonist FR139137 (1 microM). ET-1 caused a decrease in cyclic AMP in the main pulmonary arteries, an effect that was partially blocked by FR139317 but not influenced by the ET(B)-receptor antagonist BQ-788 (1 microM) or removal of the vascular endothelium. In contrast, ET-1 caused an increase in cyclic AMP in the small vessels, an effect that was blocked by BQ-788 but unaffected by FR139317. In the main pulmonary arteries, ET-1 caused enhanced incorporation of radiolabelled ADP-ribose by cholera toxin into G(i)2 in the main pulmonary artery, an indicator of its receptor-mediated activation. In summary, we have shown that in the small muscular pulmonary artery of the rat, (where ET(B) mediated vasoconstriction prevails), there is an ET(B)-mediated increase in cyclic AMP with no net effect on cyclic GMP levels. In the large arteries, (where vasoconstriction is mediated via the ET(A) receptor), there is an ET(A)-mediated increase in cyclic GMP (endothelium independent) and an ET(A)-mediated (endothelium independent) decrease in cyclic AMP.

Mobilization of intracellular Ca(2+) by endothelin-1 in rat intrapulmonary arterial smooth muscle cells

Endothelin-1 (ET-1) increases intracellular Ca(2+) concentration ([Ca(2+)](i)) in pulmonary arterial smooth muscle cells (PASMCs); however, the mechanisms for Ca(2+) mobilization are not clear. We determined the contributions of extracellular influx and intracellular release to the ET-1-induced Ca(2+) response using Indo 1 fluorescence and electrophysiological techniques. Application of ET-1 (10(-10) to 10(-8) M) to transiently (24-48 h) cultured rat PASMCs caused concentration-dependent increases in [Ca(2+)](i). At 10(-8) M, ET-1 caused a large, transient increase in [Ca(2+)](i) (>1 microM) followed by a sustained elevation in [Ca(2+)](i) (<200 nM). The ET-1-induced increase in [Ca(2+)](i) was attenuated (<80%) by extracellular Ca(2+) removal; by verapamil, a voltage-gated Ca(2+)-channel antagonist; and by ryanodine, an inhibitor of Ca(2+) release from caffeine-sensitive stores. Depleting intracellular stores with thapsigargin abolished the peak in [Ca(2+)](i), but the sustained phase was unaffected. Simultaneously measuring membrane potential and [Ca(2+)](i) indicated that depolarization preceded the rise in [Ca(2+)](i). These results suggest that ET-1 initiates depolarization in PASMCs, leading to Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+) release from ryanodine- and inositol 1,4,5-trisphosphate-sensitive stores.

The molecular basis of penile erection

Over the past two decades our understanding of the physiology and the various mediators involved in the pathway of penile erection has greatly increased. This has enabled us to develop effective pharmacological treatments for ED.

Evolution of streptozotocin-pancreatic damage in the rat: modulatory effect of endothelins on the nitridergic and prostanoid pathway

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.

Endothelin-mediated vascular growth requires p42/p44 mitogen-activated protein kinase and p70 S6 kinase cascades via transactivation of epidermal growth factor receptor

Endothelin-1 (ET-1), a potent endothelium-derived vasoconstrictor peptide, exerts a growth-promoting effect on vascular smooth muscle cells, implicating its pathogenic role in vascular remodeling. To gain insight into the cellular and molecular mechanism whereby ET-1 induces vascular growth, we studied whether transactivation of receptor tyrosine kinases, such as epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor, are required for activation of p42/p44 mitogen-activated protein (MAP) kinase and p70 S6 kinase (p70S6K), and subsequent growth-promotion by ET-1 in cultured rat vascular smooth muscle cells. Immunoblotting with antiphosphotyrosine antibody revealed that ET-1 rapidly (within 2 min) and transiently induced tyrosine phosphorylation of several proteins, among which 180-kDa protein was shown to be EGFR. ET-1 rapidly increased association of EGFR and Shc with glutathione-S-transferase-Grb2 fusion protein. The ET-1-induced activation of MAP kinase was reduced by an EGFR kinase inhibitor (AG1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG1296). AG1478 dose-dependently decreased ET-1-stimulated MAP kinase activity as well as [3H]leucine and [3H]thymidine uptake. The ET-1-induced tyrosine phosphorylation of EGFR, as well as MAP kinase activation, was inhibited by an ETA receptor antagonist and intracellular Ca2+ antagonists but not by an ETB receptor antagonist, pertussis toxin, or protein kinase C inhibitors. In addition, dominant negative mutant of H-Ras and a MAP kinase kinase (MEK-1) inhibitor (PD98059) completely blocked ET-1-induced MAP kinase activation as well as [3H]leucine and [3H]thymidine uptake. Both AG1478 and PD98059 inhibited ET-1-induced phosphorylation and activation of p70S6K. Furthermore, rapamycin, a selective inhibitor of mammalian target of rapamycin, completely blocked ET-1-stimulated [3H]leucine and [3H]thymidine uptake. These results suggest that ETA receptor-mediated vascular growth by ET-1 requires both MAP kinase and p70S6K cascades mediated partly via Ca2+-dependent EGFR transactivation.

Effects of low doses of endothelin-1 on basal vascular tone and autoregulatory vasodilation in canine coronary microcirculation in vivo

The plasma level of endothelin-1 (ET-1) increases in several cardiovascular disorders. The present study examined whether threshold doses of ET-1 affect vascular tone and autoregulatory vasodilation during a reduction in perfusion pressure in the coronary microcirculation in vivo. In anesthetized open-chest dogs, arterial microvessels in the epimyocardium were observed through a microscope equipped with a floating objective. In 6 dogs, ET-1 (10(-13) to 10(-8)mol/L) was superfused onto the epimyocardium in a cumulative fashion. In another set of dogs (n= 16), the perfusion pressure of the observed vascular bed was reduced to 60 mmHg (mild stenosis) and to 40 mmHg (severe stenosis) by a hydraulic occluder, and the microvascular responses were observed in the presence (n=9) or absence (n=7) of ET-1 (10(-12) or 10(-11) mol/L). ET-1 > or =10(-11) mol/L constricted coronary arterioles (< or =100 microm in diameter) and small arteries (>100 microm in diameter) in a dose-dependent fashion. ET-1 of 10(-12) mol/L affected neither the basal diameters nor the dilation of vessels during the pressure reduction. ET-1 of 10(-11) mol/L decreased the diameters of arterioles and small arteries before and during the mild and severe stenosis. However, ET-1 did not attenuate the percentage dilation of arterioles from the baseline in response to the mild and severe stenosis. The data indicates the following: (1) ET-1 at doses > or =10(-11) mol/L similarly constricts coronary arterioles and small arteries; (2) ET-1 at 10(-11) mol/L, which is slightly higher than the pathophysiological plasma level, increases the basal vascular tone, but does not attenuate the autoregulatory vasodilation of the coronary microcirculation.

Endothelin-induced prostacyclin production in rat aortic endothelial cells: role of calcium

Endothelin (ET) is a potent vasoconstrictor peptide, released from endothelial cells, which is associated with prostaglandin (PG) release. The mechanism by which ET causes the release of PG is not clearly understood. We used rat aortic endothelial cells to investigate the role of calcium (Ca2+) in ET-1-induced prostacyclin (PGI2) release. ET-1 (10(-9) M) produced a significant increase in PGI2 release. Pretreatment of rat aortic endothelial cells with different doses (10(-9) M and 10(-6) M) of diltiazem (voltage-sensitive L-type calcium channel blocker) produced significant inhibition of ET-1- and PDBu-induced PGI2 release. Inhibition was first noted at 10(-9) M and was complete at 10(-6) M. Conversely, pretreatment of rat aortic endothelial cells with different doses (10(-9) M and 10(-6) M) of calcium channel blockers (thapsigargin, an intracellular calcium channel blocker or conotoxin, a voltage-sensitive N-type calcium channel blocker) produced no changes on ET-1- or PDBu-induced PGI2 release. These results provide further support for the concept that PKC mediates ET-induced PGI2 release in rat aortic endothelial cells via an increase in intracellular calcium and this increase is due to the influx of extracellular calcium and not to the release of calcium from the sarcoplasmic reticulum.

Mechanism of endothelin-1-(1-31)-induced calcium signaling in human coronary artery smooth muscle cells

We have found that human chymase produces a 31-amino acid endothelin [ET-1-(1-31)] from the 38-amino acid precursor (Big ET-1). We examined the mechanism of synthetic ET-1-(1-31)-induced intracellular Ca2+ signaling in cultured human coronary artery smooth muscle cells. ET-1-(1-31) increased the intracellular free Ca2+ concentration ([Ca2+]i) in a concentration-dependent manner (10(-14)-10(-10) M). This ET-1-(1-31)-induced [Ca2+]i increase was not affected by phosphoramidon, Bowman-Birk inhibitor, and thiorphan. The ET-1-(1-31)-induced [Ca2+]i increase was not influenced by removal of extracellular Ca2+ but was inhibited by thapsigargin. ET-1-(1-31) at 10(-12) M did not cause Ca2+ influx, whereas 10(-7) M ET-1-(1-31) evoked marked Ca2+ influx, which was inhibited by nifedipine. ET-1-(1-31) also increased inositol trisphosphate formation. These results suggest that the ET-1-(1-31)-induced [Ca2+]i increase at relatively low concentrations is attributable to the release of Ca2+ from inositol trisphosphate-sensitive intracellular stores, whereas Ca2+ influx into the cells evoked by high concentration of ET-1-(1-31) probably occurs through voltage-dependent Ca2+ channels. We concluded that the physiological activity of ET-1-(1-31) may be attributable to Ca2+ mobilization from intracellular stores rather than influx of Ca2+ from extracellular space.

Cyclooxygenase inhibition potentiates the renal vascular response to endothelin-1 in humans

Vascular endothelin-receptor stimulation results in vasoconstriction and concomitant production of the vasodilators prostaglandin I2 and nitric oxide. The vascular effects of cyclooxygenase (COx) blockade (diclofenac intravenously) and the subsequent vasoconstrictor response to endothelin-1 (ET-1) infusion 30 min after diclofenac were studied in healthy men. With COx blockade, cardiac output (7%) and splanchnic (14%) and renal (12%) blood flows fell (all P < 0.001). Splanchnic blood flow returned to basal value within 30 min. Mean arterial blood pressure increased (4%, P < 0.001). Splanchnic glucose output fell (22%, P < 0.01). Subsequent ET-1 infusion caused, compared with previous ET-1 infusion without COx blockade (G. Ahlborg, E. Weitzberg, and J. M. Lundberg. J. Appl. Physiol. 77: 121-126, 1994; E. Weitzberg, G. Ahlborg, and J. M. Lundberg. Biochem. Biophys. Res. Commun. 180: 1298-1303, 1991; E. Weitzberg, G. Ahlborg, and J. M. Lundberg. Clin. Physiol. (Colch.) 13: 653-662, 1993), the same increase in mean arterial blood pressure (4%), decreases in cardiac output (13%) and splanchnic blood flow (38%), but no significant change in splanchnic glucose output. Renal blood flow reduction was potentiated (33 +/- 3 vs. 23 +/- 2%, P < 0.02), with a total reduction corresponding to 43 +/- 3% (P < 0.01 vs. 23 +/- 3%). We conclude that COx inhibition induces renal and splanchnic vasoconstriction. The selectively increased renal vascular responsiveness to ET-1 emphasizes the importance of endogenous arachidonic acid metabolites (i.e., prostaglandin I2) to counteract ET-1-mediated renal vasoconstriction.

Cellular mechanisms and role of endothelin-1-induced calcium oscillations in pulmonary arterial myocytes

The effect of endothelin (ET)-1 on both cytosolic Ca2+ concentration ([Ca2+]i) and membrane current in freshly isolated myocytes, as well as on the contraction of arterial rings, was investigated in rat main pulmonary artery (RMPA) and intrapulmonary arteries (RIPA). ET-1 (5-100 nM, 30 s) induced a first [Ca2+]i peak followed by 3-5 oscillations of decreasing amplitude. In RMPA, the ET-1-induced [Ca2+]i response was fully abolished by BQ-123 (0.1 microM). In RIPA, the response was inhibited by BQ-123 in only 21% of the cells, whereas it was abolished by BQ-788 (1 microM) in 70% of the cells. In both types of arteries, the response was not modified in the presence of 100 microM La3+ or in the absence of external Ca2+ but disappeared after pretreatment of the cells with thapsigargin (1 microM) or neomycin (0.1 microM). In RPMA myocytes clamped at -60 mV, ET-1 induced an oscillatory inward current, the reversal potential of which was close to the equilibrium potential for Cl-. This current was unaltered by the removal of external Ca2+ but was abolished by niflumic acid (50 microM). In arterial rings, the ET-1 (100 nM)-induced contraction was decreased by 35% in the presence of either niflumic acid (50 microM) or nifedipine (1 microM). These results demonstrate that ET-1 via the ETA receptor only in RMPA and both ETA and ETB receptors in RIPA induce [Ca2+]i oscillations due to iterative Ca2+ release from an inositol trisphosphate-sensitive Ca2+ store. Ca2+ release secondarily activates an oscillatory membrane Cl- current that can depolarize the cell membrane, leading to an influx of Ca2+, this latter contributing to the ET-1-induced vasoconstrictor effect.

Physiological features of visceral smooth muscle cells, with special reference to receptors and ion channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

IP3 receptor blockade fails to prevent intracellular Ca2+ release by ET-1 and alpha-thrombin

The effect of inositol 1,4,5-trisphosphate (IP3) receptor blockade on platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), endothelin-1 (ET-1), or alpha-thrombin receptor-mediated intracellular Ca2+ (Ca2+i) release was examined using fura 2 microspectrofluorometry in single Chinese hamster ovary cells and myoblasts. Blockade of the IP3 receptor was achieved by microinjection of heparin or monoclonal antibody (MAb) 18A10 into the IP3 type 1 receptor. Heparin completely inhibited Ca2+i release after flash photolysis with caged IP3 and after exposure to PDGF and FGF. In contrast, heparin failed to block Ca2+i release after alpha-thrombin and ET-1. After application of ligand, IP3 levels were five- to sevenfold higher for alpha-thrombin than for ET-1 or PDGF. IP3 levels after PDGF and ET-1 were comparable. Similar to heparin, MAb 18A10 blocked Ca2+i release after PDGF but failed to block Ca2+i release after ET-1 or alpha-thrombin. These data suggest that the mechanisms of Ca2+i release by tyrosine kinase and certain 7-transmembrane receptors may differ. Although both receptor types use the IP3-signaling system, the ET-1 and alpha-thrombin receptors may have a second, alternative mechanism for activating CA2+i release.

Endothelin-1 signaling is altered in cardiac cells from deoxycorticosterone acetate-salt hypertensive rats

The cardiac cellular effects of endothelin-1 (ET-1) on intracellular free Ca2+ concentration ([Ca2+]i) were investigated in deoxycorticosterone acetate (DOCA)-salt rats with severe cardiac hypertrophy. [Ca2+]i was measured by fura-2 methodology in ventricular cardiomyocytes and fibroblasts of DOCA-salt hypertensive and control unilaterally nephrectomized rats (Uni-Nx). Blood pressure and heart weight were increased (p < 0.01) in DOCA-salt rats compared to control rats. ET-1 (10(-12)-10(-6) M) increased [Ca2+]i in a dose-dependent manner in both cell types from control and hypertensive rats. However, ET-1-induced [Ca2+]i responses were significantly attenuated (p < 0.01) in cardiomyocytes and fibroblasts of DOCA-salt rats. Sarafotoxin S6c (S6c) increased [Ca2+]i in fibroblasts but not in cardiomyocytes. In conclusion, ET-1 dose-dependently increased [Ca2+]i in cardiomyocytes (primarily via ETA receptors) and fibroblasts (via ETA and ETB receptors). Cardiac cell ET-1 signaling pathways are blunted in DOCA-salt hypertensive rats. ET-1 may not play a critical role in the pathophysiology of the severe concentric cardiac hypertrophy present in DOCA-salt hypertensive rats.

Endothelin-1 modulation of cAMP in rat pulmonary arteries: effect of chronic hypoxia

The effect of hypoxic shock on the ability of endothelin (ET) receptors to interact with the cAMP second messenger system was assessed in rat pulmonary arteries. Whole pieces of tissue were dissected from the pulmonary arterial system of control and hypoxic (10% O2, 14 days) rats, incubated, where appropriate, with ET-1 (0.1 microM), and the levels of intracellular cAMP measured. Maintenance of rats under hypoxic conditions significantly reduced the basal cAMP levels in all of the arterial branches with the exception of the pulmonary resistance vessels, in which no change was observed. Incubation of the main and first branch extralobar pulmonary arteries from control rats with ET-1 resulted in a consistent decrease in the levels of intracellular cAMP. The ETA receptor antagonist FR139317 partially blocked this ET-1-mediated inhibition of cAMP accumulation in the main extralobar artery. In contrast, ET-1 caused a threefold increase in the levels of this cyclic nucleotide in the pulmonary resistance vessels from the normoxic rat. No ET-1-mediated reduction in intracellular cAMP levels was observed in any of the vessels isolated from hypoxic animals. All vessels showed ligand-activated increases in cAMP production. These results suggest differential modulation of cAMP in the different pulmonary arteries, either by direct activation through Gi and Gs or indirectly via a uncharacterized cross-talk mechanism.

Inhibition of voltage-gated K+ current in rat intrapulmonary arterial myocytes by endothelin-1

Although endothelin (ET)-1 is an important regulator of pulmonary vascular tone, little is known about the mechanisms by which ET-1 causes contraction in this tissue. Using the whole cell patch-clamp technique in rat intrapulmonary arterial smooth muscle cells, we found that ET-1 and the voltage-dependent K+ (Kv)-channel antagonist 4-aminopyridine, but not the Ca(2+)-activated K(+)-channel antagonist charybdotoxin (ChTX), caused membrane depolarization. In the presence of 100 nM ChTX, ET-1 (10(-10) to 10(-7) M) caused a concentration-dependent inhibition of K+ current (56.2 +/- 3.8% at 10(-7) M) and increased the rate of current inactivation. These effects of ET-1 on K+ current were markedly reduced by inhibitors of protein kinase C (staurosporine and GF 109203X) and phospholipase C (U-73122) or under Ca(2+)-free conditions and were mimicked by activators of protein kinase C (phorbol 12-myristate 13-actetate and 1,2-dioctanoyl-sn-glycerol). These data suggest that ET-1 modulated pulmonary vascular reactivity by depolarizing pulmonary arterial smooth muscle, due in part to the inhibition of Kv current that occurred via activation of the phospholipase C-protein kinase C signal transduction pathway.

Modulation of endothelin-1-induced contractions by magnesium/calcium in porcine ciliary arteries

BACKGROUND

The present study was performed to investigate the influence of extracellular magnesium on changes in contractile tone induced by endothelin-1, and on relaxations to bradykinin in isolated porcine ciliary arteries.

METHODS

Vessels were studied in a myograph system for measurement of isometric forces. Concentration-response curves (10(-10)-10(-7) M) to endothelin-1 were constructed in the presence of different concentrations (0, 1.2, 2, 10 mM) of magnesium (MgSO4). Endothelin-1-precontracted vessels (approximately 10(-8) M) were exposed to magnesium (10(-5)-10(-2) M) in the presence or absence of either the inhibitor of nitric oxide formation L-NAME (approximately 10(-4) M), or different concentrations of calcium (2.5, 5, 10 mM). In endothelin-1-precontracted vessels (10(-8) M), relaxations to bradykinin (10(-10)-10(-6) M) were conducted in the presence of different concentrations of magnesium (0, 1.2, 10 mM).

RESULTS

Contractions to endothelin-1 were reduced only in the presence of 10 mM magnesium. (1.2 mM vs 10 mM, P = 0.001). In endothelin-1-precontracted vessels, magnesium evoked complete concentration-dependent relaxations (pD2 = 3.1 +/- 0.1), which were shifted to the right by increasing extracellular concentrations of calcium (2.5 vs 5 mM, P < 0.05). L-NAME had no influence on magnesium-induced relaxations. Relaxations to bradykinin remained unaffected by changes in extracellular magnesium concentrations.

CONCLUSIONS

In a mechanism which appears to be compatible with a calcium-antagonist effect, magnesium strongly modulates changes in contractile tone evoked by endothelin-1, but has no effect on bradykinin-induced relaxations.

Flow-induced responses in cat isolated pulmonary arteries

Isolated, cannulated, endothelium-intact cat pulmonary arteries, averaging 692 +/- 104 microns in diameter, were set at a transmural pressure of 10 mmHg and monitored with a video system. Intraluminal flow was increased in steps from 0 to 1.6 ml/min by using a syringe pump. An electronic system held pressure constant by changing outflow resistance. Flow-diameter curves were generated in physiological saline solution. At constant transmural pressure, the arteries constricted in response to increased intraluminal flow. Constriction was not affected by removing extracellular Ca2+ but was abolished after treatment with ryanodine to deplete intracellular Ca2+ stores, with the endothelin-1 synthesis inhibitor phosphoramidon, with the endothelin A-receptor antagonist BQ-123, with the protein kinase C inhibitor staurosporine, or with glutaraldehyde to reduce endothelial cell deformability. The results indicate that isolated pulmonary arteries can constrict in response to intraluminal flow and suggest that constriction is mediated by endothelin-1 and depends on intracellular Ca2+ release and protein kinase C activation.

Reversal of endothelin-induced vasoconstriction by endothelium-dependent and -independent vasodilators in isolated hearts and vascular rings

Endothelin (ET-1) is a potent endogenous vasoconstrictor. Several factors increase ET-1 release in vitro and ET-1 levels increase in vivo in situations that damage blood vessels. The aim of this study was to test the activity of several differently acting vasodilator drugs on reversing or attenuating the vasoconstrictor effects of exogenously administered ET-1 in isolated guinea-pig hearts, in isolated rings with intact endothelium from canine middle cerebral and basilar arteries, and from guinea-pig aortas. Vasodilator drugs tested up to maximal concentrations were adenosine (ADE), nitroprusside (NP), acetylcholine (ACH), nifedipine (NIF), and butanedione monoxime (BDM), an excitation-uncoupling agent. Variables measured in isolated hearts included coronary flow, percentage oxygen extraction (% O2E), left ventricular pressure (LVP), and myocardial oxygen consumption. It was found that ADE, NP, ACH, and BDM each attenuated the 60% decrease in coronary flow and 20% increase in % O2E elicited by 0.5 nM ET-1 in isolated hearts, but only BDM restored coronary flow, whereas BDM and ADE both restored % O2E. In isolated rings constricted with 20 nM ET-1, BDM restored tone equivalent to that by papaverine, whereas NP and NIF only attenuated the vasoconstriction elicited by ET-1. Ring experiments also demonstrated that the vasodilatory effect of BDM was independent of nitric oxide-dependent pathways and that BDM attenuated vasoconstriction resulting from increased bath KCl. The study suggests that drugs affecting intracellular Ca2+ with a mechanism of action downstream from cell-membrane receptors or intracellular messengers may be more effective for reversing the constrictor effect of ET-1. NP, however, would be a better clinical choice for reversing ET-1-induced vasoconstriction.

Endothelin production in cultured vascular smooth muscle cells--modulation by the atrial, brain, and C-type natriuretic peptide system

We examined the regulatory mechanisms of endothelin-1 (ET-1) production in cultured rat vascular smooth muscle cells (VSMC) with a special focus on the roles of protein kinase C (PKC)- and cyclic guanosine-3',5'-monophosphate (GMP)-mediated signaling systems. Effects of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP) on angiotensin II (Ang II)-, and arginine vasopressin (AVP)-induced production of ET-1 were examined in cultured rat aortic VSMC. Ang II and AVP stimulated ET-1 production in a concentration-dependent manner through angiotensin subtype 1 (AT1) and vasopressin subtype 1 (V1) receptors, respectively. The stimulatory effects of Ang II and AVP were markedly abolished in PKC-depleted cells. Rat ANP (1-28), rat BNP-45, and rat CNP-22 potently inhibited Ang II- and AVP-stimulated ET-1 production in a concentration-dependent manner, respectively. The inhibitory effect by CNP on ET-1 production was paralleled by an increase in the cellular level of cyclic GMR.8-Bromo cyclic GMP reduced the stimulated ET-1 production by Ang II and AVP. These results indicate that Ang II and AVP stimulate ET-1 production in cultured rat VSMC through AT1 and V1 receptors by a mechanism probably involving activation of PKC, and that ANP, BNP, and CNP inhibit this stimulated production through a cyclic GMP-dependent process.

Activation of BK(Ca) channel via endothelin ET(A) receptors in porcine coronary artery smooth muscle cells

It has been demonstrated previously that endothelin-1 stimulates the Ca2+-activated K+ (BK(Ca)) channel activity in porcine coronary artery smooth muscle cells. The purpose of the present study was to delineate the endothelin receptor subtype involved in this action. In receptor binding studies, [125I]endothelin-1 was shown to bind to the homogenate of porcine primary coronary artery smooth muscle cells in a single class of binding sites with K(D) and Bmax values of 73 pM and 99 fmol/mg protein, respectively. Furthermore, endothelin-1 and endothelin-3 displaced the binding of [125I]endothelin-1 to these cells with respective IC50 values of 70 and 17000 pM, a 240-fold difference in potency. The effects of endothelin-3 on the activity of the BK(Ca) channel in porcine coronary artery smooth muscle cells were examined using the cell-attached patch-clamp technique. Similar to endothelin-1, endothelin-3 also exhibited a bell-shaped concentration-response curve. A maximal increase of 95% in channel open-state probability (Po) was induced by 100 nM endothelin-3 as compared with the 320% increase in Po by 1 nM endothelin-1. Thus, endothelin-1 was about 100-fold more potent and 3.4-fold more efficacious than endothelin-3 in this action. Both the receptor binding and the electrophysiological results suggest that the effects of endothelins on the BK(Ca) channel are mediated through the endothelin ET(A) receptor subtype.

Modulation of endothelin-induced intracellular Ca2+ mobilization by interleukin-1 beta and lipopolysaccharide in C6 rat glioma cells

We have investigated the effects of interleukin (IL)-1 beta and lipopolysaccharide (LPS) on endothelin (ET)-induced intracellular Ca2+ rise in C6 rat glioma cells in order to study the mechanisms of their effects on Ca2+ signaling systems. Pretreatment with IL-1 beta (10(3) U/mL) and LPS (1 microgram/mL) for 24 h significantly inhibited 100 nM ET-1-induced increase in intracellular Ca2+ either in the presence or absence of external Ca2+. Their inhibitory effects were in dosedependent (IL-1 beta; 50-1000 U/mL, LPS; 10-1000 ng/mL) and time-dependent (12-24 h) manners. A tyrosine kinase antagonist genistein (50 microM) but not a protein kinase C inhibitor H7 (30 microM) prevented the inhibition of the ET response by IL-1 beta and LPS. These results suggest that activation of tyrosine kinase may be essential for the inhibition of the ET receptor-mediated Ca2+ signaling systems by IL-1 beta and LPS.

Intralobular innervation and lipocyte contractility in the liver

In the liver of humans, guinea pigs, cats, and tupaia, nerve endings are distributed all over the hepatic lobules from the portal spaces to the centralobular spaces. Nerve endings in the intralobular spaces are located mainly in the space of Disse, and are closely related to lipocytes. In the human liver, various neurotransmitters such as substance P (SP) exist in the nerve endings. Lipocytes are believed to contract through these substances. In fact, the contraction of lipocytes is induced by SP. Moreover, lipocytes possess endothelin (ET) receptors (ETA, ETB), and the cells are contracted by ET-1 by way of ET receptors in the autocrine or paracrine mechanism. Contraction of lipocytes seems to be related to the enhancement of the intracellular Ca2+ and inositol phosphates. In addition, alpha-smooth muscle actin, which is a contractile protein, exists in the cytoplasm of lipocytes. Lipocyte contractility may be similar to that of vascular smooth muscle cells. On the other hand, prostaglandin E2, Iloprost, and adrenomedullin cause the elevation of c-AMP levels in lipocytes and relax the cells. In addition, lipocytes produce nitric oxide (NO) and inhibit contractility by an autocrine mechanism related to NO. In this way, lipocytes appear to be associated with the regulation of hepatic sinusoidal microcirculation by contraction and relaxation. In the cirrhotic liver, intralobular innervation is decreased or absent, but ET-1 and NO are overexpressed. These phenomena indicate that lipocytes may play an important role in the sinusoidal microcirculation through these agents rather than through intralobular innervation in liver cirrhosis.