Possible role of Na(+)-K(+)-ATPase in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide

Update on Treatment Options for Stuttering Priapism

Purpose of Review

There is a paucity of peer-reviewed evidence to guide medical management of stuttering priapism. The purpose of this review is to summarize the current understanding regarding the pathophysiology of priapism and management options for stuttering priapism.

Recent Findings

Conducting large-scale, randomized, placebo-controlled trials that elucidate the optimal treatment of stuttering priapism is challenging. Therefore, recent treatment guidelines are based upon small case series, retrospective studies, and expert opinions. Nonetheless, multiple compounds from various drug classes have shown promise in treating stuttering priapism, and a few pharmacotherapies such as Crizanlizumab are currently under active investigation.

Summary

Stuttering priapism is an under-investigated disorder with a complex pathophysiology. Currently, there is no wildly adopted universal therapeutic strategy. Further research is warranted to identify the appropriate treatment of stuttering priapism and to determine the long-term side effects of current pharmacotherapies.

Review of a Potential Novel Approach for Erectile Dysfunction: Light-Controllable Nitric Oxide Donors and Nanoformulations

INTRODUCTION

Nitric oxide (NO) is known as the key factor involved in initiating and maintaining an erection. Therefore, NO supplementation may be a target for erectile dysfunction. However, the use of NO donors carries the risk of systemic side effects. Recently, novel NO donors, such as a light-controllable NO donor or NO donor in nanoparticles, have been developed. In this review, we introduce such novel compounds and methods.

AIM

To review light-controllable and nanotechnological NO donors for the treatment of erectile dysfunction.

METHODS

We conducted a review of relevant articles via PubMed in December 2018.

MAIN OUTCOME MEASURES

In this study, we reviewed novel NO donors, such as light-controllable NO donors and nanotechnological NO donors.

RESULTS

Some light-controllable NO donors have been already reported. A light-controllable NO donor without metal has also been recently developed. Light-controllable NO donors and light irradiation can control the release of NO spatiotemporally. In an isometric tension study, a relaxing response of the aortic tissue and penile corpus cavernosum was observed under light irradiation with a light-controllable NO donor. In addition, the effects of nanoparticles and nanoemulsions containing sodium nitrate on erectile function have been reported. The nanoformulation containing an NO donor can likely be absorbed percutaneously and, thus, enhance erectile function.

CONCLUSIONS

A light-controllable NO donor might be useful for treating erectile dysfunction because light irradiation is a convenient method to be applied for patients. However, light permeability might be an issue that needs to be solved. Nanoformulation is also likely to be a useful, non-invasive approach. The application of these procedures and compounds may help in the development of future treatments for erectile dysfunction. Hotta Y, Kataoka T, Taiki Mori T, et al. Review of a Potential Novel Approach for Erectile Dysfunction: Light-Controllable Nitric Oxide Donors and Nanoformulations. Sex Med Rev 2020;8:297-302.

The Relaxant Mechanisms of Hydrogen Sulfide in Corpus Cavernosum

In several animal and human studies, the contribution of the endothelium, nitric oxide/soluble guanosine monophosphate (NO/cGMP) pathway, adenylyl cyclase, phosphodiesterase (PDE), potassium (K⁺) channels, L-type calcium channels, Na⁺-K⁺-ATPase, muscarinic acetylcholine receptors, RhoA/Rho-kinase pathway, and cyclooxygenase (COX)/arachidonic acid cascade on the relaxant mechanism of L-cysteine/H₂S pathway in corpus cavernosum has been investigated. In this chapter the relaxant mechanisms of H₂S in corpus cavernosum is discussed with data available in the current relevant literature. Also, in vitro experimental procedure for mice corpus cavernosum which used to investigate the relaxant effect of H₂S is given in detail.

Erectile Dysfunction in Heme-Deficient Nitric Oxide-Unresponsive Soluble Guanylate Cyclase Knock-In Mice

INTRODUCTION

The nitric oxide (NO), soluble guanylate cyclase (sGC), and cyclic guanosine monophosphate (cGMP) pathway is the leading pathway in penile erection.

AIM

To assess erectile function in a mouse model in which sGC is deficient in heme (apo-sGC) and unresponsive to NO.

METHODS

Mutant mice (sGCβ₁^ki/ki) that express an sGC enzyme that retains basal activity but fails to respond to NO because of heme deficiency (apo-sGC) were used. Isolated corpora cavernosa from sGCβ₁^ki/ki and wild-type mice were mounted in vitro for isometric tension recordings in response to sGC-dependent and -independent vasorelaxant agents. In addition, the erectile effects of some of these agents were tested in vivo at intracavernosal injection.

MAIN OUTCOME MEASURES

In vitro and in vivo recordings of erectile responses in sGCβ₁^ki/ki and wild-type mice after stimulation with sGC-dependent and -independent vasorelaxant agents.

RESULTS

NO-induced responses were abolished in sGCβ₁^ki/ki mice in vitro and in vivo. The ability of the heme-dependent, NO-independent sGC stimulator BAY 41-2272 to relax the corpora cavernosa was markedly attenuated in sGCβ₁^ki/ki mice. In contrast, the relaxation response to the heme- and NO-independent sGC activator BAY 58-2667 was significantly enhanced in sGCβ₁^ki/ki mice. The relaxing effect of sGC-independent vasorelaxant agents was similar in wild-type and sGCβ₁^ki/ki mice, illustrating that the observed alterations in vasorelaxation are limited to NO-sGC-cGMP-mediated processes.

CONCLUSION

Our results suggest that sGC is the sole target of NO in erectile physiology. Furthermore, this study provides indirect evidence that, in addition to sGCα₁β₁, sGCα₂β₁ is important for erectile function. In addition, the significant relaxation observed in sGCβ₁^ki/ki mice with the cumulative addition of the sGC activator BAY 58-2667 indicates that sGC activators might offer value in treating erectile dysfunction.

Characterization of relaxant mechanism of H2 S in mouse corpus cavernosum

The aim of this study was to investigate the mechanism of H2 S-induced relaxation in mouse corpus cavernosal tissue. l-cysteine (10(-6) × 10(-3) mol/L) and exogenous H2 S (NaHS; 10(-6) to 10(-3) mol/L) induced concentration-dependent relaxation. l-cysteine-induced relaxations was reduced by d,l-propargylglycine, a cystathionine gamma lyase (CSE) inhibitor but not influenced by aminooxyacetic acid, a cystathionine beta synthase (CBS) inhibitor. l-cysteine induced relaxations, but not of those of H2 S diminished in endothelium-denuded tissues. N(ω) -nitro-l-arginine (l-NA; 10(-4) mol/L), a nitric oxide synthase inhibitor, and ODQ (10(-4) mol/L), a guanylyl cyclase inhibitor, increased the H2 S-induced relaxation. Zaprinast (5 × 10(-6) mol/L) and sildenafil (10(-6) mol/L), phosphodiesterase inhibitors, inhibited H2 S-induced relaxation. Adenylyl cyclase inhibitors N-ethylmaleimide (2.5 × 10(-5) mol/L) and SQ22536 (10(-4) mol/L) reduced relaxation to H2 S. Also, H2 S-induced relaxation was reduced by KCl (50 mmol/L), 4-aminopyridine (10(-3) mol/L), a Kv inhibitor, glibenclamide (10(-5) mol/L), a KATP inhibitor or barium chloride (10(-5) mol/L), a KIR inhibitor. However, H2 S-induced relaxation was not influenced by apamin (10(-6) mol/L), a SKC a (2+) inhibitor, charybdotoxin (10(-7) mol/L), an IKC a (2+) and BKC a (2+) inhibitor or combination of apamin and charybdotoxin. Nifedipine (10(-6) mol/L), an L-type calcium channel blocker and atropine (10(-6) mol/L), a muscarinic receptor blocker, inhibited H2 S-induced relaxation. However, H2 S-induced relaxation was not influenced by ouabain (10(-4) mol/L), a Na(+) /K(+) -ATPase inhibitor. This study suggests that H2 S endogenously synthesizes from l-cysteine by CSE endothelium-dependent in mouse corpus cavernosum tissue, and exogenous H2 S may cause endothelium-independent relaxations via activation of K channels (KATP channel, KV channels, KIR channels), L-type voltage-gated Ca(2+) channels, adenylyl cyclase/cAMP pathway and muscarinic receptor, and there is the interaction between H2 S and NO/cGMP.

Management of Recurrent Ischemic Priapism 2014: A Complex Condition with Devastating Consequences

INTRODUCTION

The management of recurrent ischemic priapism (RIP) is not clearly defined. Given the rarity of this condition, most treatment options are supported at best by level 3 or 4 evidence.

AIM

In this article, we review the current literature regarding the pathophysiology and management of RIP and discuss the risks and benefits associated with each option, which includes ketoconazole (KTZ), 5-α-reductase inhibitors and other hormonal therapies, phosphodiesterase type 5 (PDE5) inhibitors, intracavernosal sympathomimetic injection, oral sympathomimetic agents, and other investigational therapies.

METHODS

A comprehensive literature review was performed regarding the management options for RIP.

MAIN OUTCOME MEASURE

To examine the pathophysiology of RIP and evaluate the treatment options.

RESULTS

Multiple agents have been investigated to manage RIP. KTZ, finasteride, anti-androgens, gonadotropin-releasing hormone agonists, and estrogen have been shown to be effective in several reports, though some of these agents may have significant hormonal side effects. PDE5 inhibitors currently appear to be well tolerated in this patient population, though evidence of its efficacy is limited. Intracavernosal α-agonist therapy may be used to treat episodes of priapism after they occur. Very limited data suggest terbutaline, oral α-agonists, digoxin, hydroxyurea, and gabapentin may have a role in RIP management.

CONCLUSIONS

An ideal management strategy for RIP should focus on prevention of priapic episodes using an effective, well-tolerated, cost-effective medication. We currently have several proposed options, with varying efficacy rates and side effect profiles. While significant advancements in our understanding and management of stuttering priapism have been made within the past few years, clearly continuing research and clinical studies are needed to guide our management of this disease process. Hoeh MP and Levine LA. Management of recurrent ischemic priapism 2014: A complex condition with devastating consequences. Sex Med Rev 2015;3:24-35.

Anatomy and physiology of genital organs - men

Male sexual functions involve a number of organs and structures in genitalia whose role is to produce fertilizing gametes and to allow female-partner insemination. The testes belong to the reproductive and endocrine systems as they synthesize spermatozoa and androgens, and are under finely regulated hormonal control by the hypothalamopituitary axis. Sexual responses are controlled by a complex and coordinated interplay of both the somatic and the autonomic nervous system in multiple components of the brain, spinal cord, and relevant peripheral organs. Erectile bodies are an essential element of the penis and engorgement of the penis with blood leads to penile tumescence. Blood engorgement is due to relaxation of smooth-muscle cells of erectile tissue and endothelium of the penile arteries. The penis gains additional rigidity when the ischiocavernosus muscles contract. Stimuli from peripheral and/or central origins activate particular spinal nuclei, causing penile erection. Ejaculation consists of two phases, emission and expulsion, which correspond, respectively, to secretion of the different components of the semen by sex glands and forceful expulsion of semen due to rhythmic contractions of the bulbospongiosus muscle. A spinal generator of ejaculation integrates genital stimuli and sexual cues and, when the excitatory threshold is reached, triggers ejaculation by orchestrating the activation of autonomic and somatic pathways commanding the peripheral events of ejaculation.

Management of priapism: an update for clinicians

Priapism is a prolonged erection that persists beyond or is unrelated to sexual stimulation. It is associated with significant morbidity: psychological, socioeconomic, and physical, including pain and potentially irreversible compromise of erectile function. There are three major types of priapism: ischemic, nonischemic, and stuttering. Establishing the type of priapism is paramount to safely and effectively treating these episodes. Ischemic priapism represents a urological emergency. Its treatment may involve aspiration/irrigation with sympathomimetic injections, surgical shunts, and as a last resort, penile prosthesis implantation. Nonischemic priapism results from continuous flow of arterial blood into the penis, most commonly related to penile trauma. This is not an emergency and may be managed conservatively initially, as most of these episodes are self-limiting. Stuttering priapism involves recurrent self-limiting episodes of ischemic priapism. The primary goal of therapy is prevention, but acute episodes should be managed in accordance with guidelines for ischemic priapism. In this paper we review the diagnosis and treatment of the three priapism variants, as well as discuss future targets of therapy and novel targets on the horizon.

Medical management of ischemic stuttering priapism: a contemporary review of the literature

Priapism is defined as a prolonged and persistent erection of the penis without sexual stimulation. This is a poorly understood disease process with little information on the pathophysiology of this erectile disorder. Complications from this disorder are devastating due to the irreversible erectile damage and resultant erectile dysfunction (ED). Stuttering priapism, though relatively rare, affects a high prevalence of men with sickle-cell disease (SCD) and presents a challenging problem with guidelines for treatment lacking or resulting in permanent ED. The mechanisms involved in the development of priapism in this cohort are poorly characterized; therefore, medical management of priapism represents a therapeutic challenge to urologists. Additional research is warranted, so we can effectively target treatments for these patients with prevention as the goal. This review gives an introduction to stuttering priapism and its clinical significance, specifically with regards to the patient with SCD. Additionally, the proposed mechanisms behind its pathophysiology and a summary of the current and future targets for medical management are discussed.

Regulation of NO-dependent acetylcholine relaxation by K+ channels and the Na+-K+ ATPase pump in porcine internal mammary artery

This study was designed to determine whether K+ channels play a role in nitric oxide (NO)-dependent acetylcholine relaxation in porcine internal mammary artery (IMA). IMA segments were isolated and mounted in organ baths to record isometric tension. Acetylcholine-elicited vasodilation was abolished by muscarinic receptor blockade with atropine (10(-6)M). Incubation with indomethacin (3 x 10(-6)M), superoxide dismutase (150 U/ml) and bosentan (10(-5)M) did not modify the acetylcholine response ruling out the participation of cyclooxygenase-derivates, reactive oxygen species or endothelin. The relaxation response to acetylcholine was strongly diminished by NO synthase- or soluble guanylyl cyclase-inhibition using L-NOArg (10(-4)M) or ODQ (3 x 10(-6)M), respectively. The vasodilation induced by acetylcholine and a NO donor (NaNO(2)) was reduced when rings were contracted with an enriched K+ solution (30 mM), by voltage-dependent K+ (K(v)) channel blockade with 4-amynopiridine (4-AP; 10(-4)M), by Ca(2+)-activated K+ (K(Ca)) channel blockade with tetraethylammonium (TEA; 10(-3)M), and by apamin (5 x 10(-7)M) plus charybdotoxin (ChTx; 10(-7)M) but not when these were added alone. In contrast, large conductance K(Ca) (BK(Ca)), ATP-sensitive K+ (K(ATP)) and inwardly rectifying K+ (K(ir)) channel blockade with iberiotoxin (IbTx; 10(-7)M), glibenclamide (10(-6)M) and BaCl(2) (3 x 10(-5)M), respectively, did not alter the concentration-response curves to acetylcholine and NaNO(2). Na+-K+ ATPase pump inhibition with ouabain (10(-5)M) practically abolished acetylcholine and NaNO(2) relaxations. Our findings suggest that acetylcholine-induced relaxation is largely mediated through the NO-cGMP pathway, involving apamin plus ChTx-sensitive K+ and K(v) channels, and Na+-K+-ATPase pump activation.

In vitro and in vivo studies on the importance of the soluble guanylyl cyclase α1 subunit in penile erection

PURPOSE

Soluble guanylyl cyclase (sGC), which plays a pivotal role in penile erection, is a heterodimer build up by an α and a β subunit. For both subunits two isoforms have been characterized, but only the sGCα(1)β(1) and sGCα(2)β(1) isoforms seem to be functionally active. To elucidate the functional role of the sGCα(1)β(1) heterodimer in the mechanism of erection, experiments were performed in vivo and on isolated corpora cavernosa (CC) using sGCα(1)(-/-) mice.

MATERIALS AND METHODS

For the in vivo study sGC-dependent and -independent vasorelaxing agents were injected intracavernosally in sGCα(1)(-/-) and sGCα(1)(+/+) mice and the rise in intracavernosal pressure was recorded. For the in vitro study, isolated CC tissues from sGCα(1)(-/-) and sGCα(1)(+/+) mice were mounted in organ baths for isometric tension recording and concentration-dependent curves were obtained for sGC-dependent and -independent vasorelaxing agents. These experiments were performed on 2 different mice strains (129SvEvS7 and C57BL6/J) to determine potential strain differences.

RESULTS

The responses in sGCα(1)(-/-) after administration of the NO-donors, sodium nitroprusside (SNP) and spermine-NO, and to electrical stimulation are significantly reduced although not completely abolished. Responses to sGC-independent vasorelaxing agents are similar in sGCα(1)(-/-) and sGCα(1)(+/+) mice from both strains suggesting that the decreased potential of smooth muscle relaxation is not related to structural changes or changes in the pathway downstream sGC.

CONCLUSION

This study illustrates the strain-independent importance of the sGCα(1)β(1) heterodimer, although remaining vasorelaxing responses in the sGCα(1)(-/-) mice suggest a complementary role for the sGCα(2)β(1) isoform or (an) sGC-independent mechanism(s).

Phospholemman: its role in normal cardiac physiology and potential as a druggable target in disease

Phospholemman (PLM) is a member of the FXYD ('fix-it') family of proteins many of which have now been identified as tissue-specific regulators of the Na/K ATPase. PLM (FXYD1) is the primary sarcolemmal substrate for PKC and PKA in the heart. We have recently identified PLM as a novel accessory protein that forms part of the cardiac Na/K ATPase pump complex. PLM regulates Na/K pump activity in a way analogous to the regulation of SERCA by phospholamban-that is un-phosphorylated PLM exerts a tonic inhibition on the Na/K pump, while phosphorylated PLM relieves this inhibition and stimulates pump activity. This process is likely to be fundamentally important in the normal physiological regulation of the cell particularly at high heart rates and, as briefly reviewed in this article, is also likely to offer novel therapeutic targets for the treatment of diseases such as cardiac hypertrophy and heart failure.

The Management of Stuttering Priapism within a Specialist Unit—A 25-Year Experience

Introduction:

Stuttering priapism is a rare condition characterised by recurrent prolonged erections. The condition is common in patients with sickle cell disease although a significant proportion suffer from idiopathic stuttering priapism. The management of this condition is mainly through anecdotal reports.

Methods:

We have retrospectively reviewed 60 patients with this condition in a single centre over a 25-year period. Risk factors were identified and the outcomes of both pharmacological therapies and surgical interventions were recorded.

Results:

Erections were characteristically nocturnal and painful in nature and lasted up to 72h in some patients. Analysis of the outcomes of both medical and surgical interventions has shown that the use of hormone analogues such as cyproterone acetate is the most efficacious treatment option as it allows a successful control of their erections without a significant loss of libido in 86% of patients. The most successful surgical option was the insertion of a penile prosthesis.

Conclusion:

Due to the rarity of this condition, the management is variable and based on anecdotal evidence. This study has reported our experience of the most efficacious treatment options for this condition. We also discuss the potential therapeutic role of PDE-5 inhibitors in this condition.

Stuttering priapism--a review of the therapeutic options

INTRODUCTION

Priapism is a urological emergency which is commonly classified into low-flow and high-flow priapism. Immediate intervention is required for low-flow cases as the development of ischaemia ultimately leads to long-term erectile dysfunction. Stuttering or recurrent priapism is less well understood. This subtype is characterised by short-lived painful erections and is commonly encountered in patients with sickle cell disease.

METHODS

A systematic review of the treatment options available for stuttering priapism is presented combined with our own experience in managing this condition over a period of 25 years.

RESULTS

Although numerous medical treatment options have been reported, the majority are through small trials or anecdotal reports.

CONCLUSIONS

Stuttering priapism is a condition which is still not well understood and there is no standardised algorithm for the management of this condition. A multicentre randomised trial is required to evaluate the treatment options.

Role of the soluble guanylyl cyclase alpha1-subunit in mice corpus cavernosum smooth muscle relaxation

Soluble guanylyl cyclase (sGC) is the major effector molecule for nitric oxide (NO) and as such an interesting therapeutic target for the treatment of erectile dysfunction. To assess the functional importance of the sGCalpha(1)beta(1) isoform in corpus cavernosum (CC) relaxation, CC from male sGCalpha(1)(-/-) and wild-type mice were mounted in organ baths for isometric tension recording. The relaxation to endogenous NO (from acetylcholine, bradykinin and electrical field stimulation) was nearly abolished in the sGCalpha(1)(-/-) CC. In the sGCalpha(1)(-/-) mice, the relaxing influence of exogenous NO (from sodium nitroprusside and NO gas), BAY 41-2272 (NO-independent sGC stimulator) and T-1032 (phosphodiesterase type 5 inhibitor) were also significantly decreased. The remaining exogenous NO-induced relaxation seen in the sGCalpha(1)(-/-) mice was significantly decreased by the sGC-inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The specificity of the impairment of the sGC-related responses was demonstrated by the unaltered relaxations seen with forskolin (adenylyl cyclase activator) and 8-pCPT-cGMP (cGMP analog). In conclusion, the sGCalpha(1)beta(1) isoform is involved in corporal smooth muscle relaxation in response to NO and NO-independent sGC stimulators. The fact that there is still some effect of exogenous NO in the sGCalpha(1)(-/- mice suggests the contribution of (an) additional pathway(s).

Nitric oxide activates leak K+ currents in the presumed cholinergic neuron of basal forebrain

Learning and memory are critically dependent on basal forebrain cholinergic (BFC) neuron excitability, which is modulated profoundly by leak K(+) channels. Many neuromodulators closing leak K(+) channels have been reported, whereas their endogenous opener remained unknown. We here demonstrate that nitric oxide (NO) can be the endogenous opener of leak K(+) channels in the presumed BFC neurons. Bath application of 1 mM S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, induced a long-lasting hyperpolarization, which was often interrupted by a transient depolarization. Soluble guanylyl cyclase inhibitors prevented SNAP from inducing hyperpolarization but allowed SNAP to cause depolarization, whereas bath application of 0.2 mM 8-bromoguanosine-3',5'-cyclomonophosphate (8-Br-cGMP) induced a similar long-lasting hyperpolarization alone. These observations indicate that the SNAP-induced hyperpolarization and depolarization are mediated by the cGMP-dependent and -independent processes, respectively. When examined with the ramp command pulse applied at -70 mV under the voltage-clamp condition, 8-Br-cGMP application induced the outward current that reversed at K(+) equilibrium potential (E(K)) and displayed Goldman-Hodgkin-Katz rectification, indicating the involvement of voltage-independent K(+) current. By contrast, SNAP application in the presumed BFC neurons either dialyzed with the GTP-free internal solution or in the presence of 10 muM Rp-8-bromo-beta-phenyl-1,N(2)-ethenoguanosine 3',5'-cyclic monophosphorothioate sodium salt, a protein kinase G (PKG) inhibitor, induced the inward current that reversed at potentials much more negative than E(K) and close to the reversal potential of Na(+)-K(+) pump current. These observations strongly suggest that NO activates leak K(+) channels through cGMP-PKG-dependent pathway to markedly decrease the excitability in BFC neurons, while NO simultaneously causes depolarization by the inhibition of Na(+)-K(+) pump through ATP depletion.

Physiological regulation of penile arteries and veins

Recent experimental evidence suggests that arterial insufficiency precedes the structural and functional changes in corpora cavernosa (CC) leading to organic erectile dysfunction (ED). The present review gives an overview of the physiological factors involved in the regulation of penile vasculature. Sympathetic nerves maintain flaccidity and tonically released noradrenaline induces vasoconstriction of both arteries and veins through alpha(1)- and alpha(2)-postsynaptic receptors and downregulates its own release and that of nitric oxide (NO) through alpha(2)-presynaptic receptors. The sympathetic cotransmitter neuropeptide Y (NPY) modulates noradrenergic vasoconstriction in penile small arteries by both enhancing and depressing noradrenaline contractions through Y(1)- and Y(2)-postsynaptic and a NO-independent atypical endothelial receptor, respectively. Activation of alpha(1)-adrenoceptors involves both Ca(2+) influx through L-type and receptor-operated Ca(2+) channels (ROC) and Ca(2+) sensitization mechanisms mediated by protein kinase C (PKC), tyrosine kinases (TKs) and Rho kinase (RhoK). In addition, RhoK can regulate Ca(2+) entry in penile arteries upon receptor stimulation. Vasodilatation of penile arteries and large veins during erection is mediated by neurally released NO. The subsequent increased arterial inflow to the cavernosal sinoids and shear stress on the endothelium lining penile arteries activates endothelial NO production through Akt phosphorylation of endothelial NO synthase (eNOS). NO stimulates guanylate cyclase and increased cyclic guanin 3'-monophosphate (cGMP) levels in turn activate protein kinase G (PKG), which enhances K(+) efflux through Ca(2+)-activated (K(Ca)) and voltage-dependent Ca(2+) (K(v)) channels in penile arteries and veins, respectively. PKG-mediated decrease in Ca(2+) sensitivity and its regulation by RhoK remains to be clarified in penile vasculature. Phosphodiesterase type 5 (PDE5) inhibitors are potent vasodilators of penile resistance arteries and increase the content and effects of basally released endothelial NO. Endothelium-dependent relaxations of penile small arteries also include an endothelium-derived hyperpolarizing factor (EDHF)-type response, which is impaired in diabetes and hypertension-associated ED. Locally produced contractile and relaxant prostanoids regulate penile venous and arterial tone, respectively. The latter activates prostaglandin I (IP) and prostaglandin E (EP) receptors coupled to adenylate cyclase and to the increase of cyclic adenosine monophosphate (cAMP) levels, which in turn stimulates K(+) efflux through ATP-sensitive K(+) (K(ATP)) channels. There is a crosstalk between the cGMP and cAMP signaling pathways in penile small arteries. Relevant issues such as the mechanisms underlying the excitation-secretion coupling of the endothelial cells, as well as those involved in cell proliferation and vascular remodeling of the penile vasculature remain to be elucidated. In addition, only few studies have investigated the changes in structure and function of penile arteries in cardiovascular risk situations leading to ED.

In vitro models: research in physiology and pharmacology of the lower urinary tract

The physiology and pharmacology of the lower urinary tract has advanced based, in part, due to the in vitro assays that have facilitated this exploration. Such assays have led to the development of novel and selective molecules that have been used to characterize different receptor and enzyme systems in the larger context of in vivo pharmacology. These assays can be classified by sites of action of drugs into the following categories: receptors, effector enzymes and enzymes that terminate the responses. In this review, representative assays are presented based on our experience in male erectile dysfunction.

Erectile Dysfunction in Heart Failure Patients

Chronic heart failure (HF) and erectile dysfunction (ED) are 2 highly prevalent disorders that frequently occur concomitantly. Coronary artery disease, HF, and ED share several common risk factors, including diabetes mellitus, hypertension, smoking, and dyslipidemia. Additionally, the distinct physiologic sequelae of HF create unique organic and psychologic factors contributing to ED in this patient population. Standard HF therapy with beta-receptor blockers, digoxin and thiazide diuretics may worsen sexual dysfunction owing to medication side effects. This may, in turn, lead to noncompliance in misguided efforts to retain satisfactory sexual activity, with secondary worsening of cardiac capacity. This review describes the unique aspects of ED in the HF population.

Physiology of erectile function

INTRODUCTION

There are numerous investigations concerning the balance and interactions between relaxant and contractile factors regulating penile smooth muscle (arterial and trabecular) tone, the determinant of penile flaccidity or erection. Enhanced knowledge of erectile physiology may improve management of men with erectile dysfunction. Aim. To provide state-of-the-art knowledge on the physiology of erectile function.

METHODS

An international consultation in collaboration with the major urology and sexual medicine associations assembled over 200 multidisciplinary experts from 60 countries into 17 committees. Committee members established specific objectives and scopes for various male and female sexual medicine topics. The recommendations concerning state-of-the-art knowledge in the respective sexual medicine topic represent the opinion of experts from five continents developed in a process over a two-year period. Concerning the physiology of erectile function and pathophysiology of erectile dysfunction committee, there were seven experts from five countries.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Key roles in the mechanism determining the tone of penile smooth muscle are played by the rise of the intracellular concentration of free calcium and the sensitivity of the contractile machinery to calcium, endothelial health, endothelium-derived nitric oxide, endothelium-derived hyperpolarizing factor (EDHF), neuronal nitric oxide, cyclic guanosine monophosphate-dependent protein kinase and phosphodiesterase type 5.

CONCLUSIONS

A number of new mechanisms have been identified for the local regulation of penile smooth muscle contractility and therefore penile erection. Molecules participating in these pathways can be considered targets for the development of new treatments to treat erectile dysfunction.

Why do patients with heart failure suffer from erectile dysfunction? A critical review and suggestions on how to approach this problem

Chronic heart failure (HF) is an increasingly common cardiovascular disorder. The goal of health-care providers is to optimize quality of life in this population, including sexual health. Up to 75% of patients with HF report erectile dysfunction (ED). As HF is a condition with distinct physiologic sequelae, some unique organic and psychological factors contributing to ED in this patient population have been identified, along with risk factors common to the development of coronary artery disease, HF and ED. This review describes contributing factors to ED in the setting of HF and highlights treatment considerations for this distinct patient population.

Interaction between spontaneous and neurally mediated regulation of smooth muscle tone in the rabbit corpus cavernosum

Interaction between spontaneous and neurally mediated regulation of tone in the corpus cavernosum smooth muscle (CCSM) of the rabbit was investigated. Changes in isometric muscle tension, intracellular Ca2+ concentration ([Ca2+]i) and membrane potential were recorded. CCSM developed spontaneous contractions, transient increases in [Ca2+]i (Ca2+ transients) and depolarizations. This spontaneous activity was abolished by blocking L-type Ca2+ channels (nicardipine, 1 mum), sarcoplasmic reticulum Ca2+ pump activity (cyclopiazonic acid, 10 microm), Ca2(+)-activated Cl- channels (niflumic acid, 10 mum) or cyclooxygenase-2 (COX-2; NS-398, 1 microm). Transmural nerve stimulation initiated either alpha-adrenergic contractions or nitrergic relaxations of CCSM depending on the level of muscle tone. NS-398 suppressed nerve-evoked contractions by about 70% but caused only a 40% reduction in the corresponding Ca2+ transient. Blocking nitric oxide synthase with N(omega)-nitro-l-arginine (LNA, 100 microm) reinforced nerve-evoked Ca2+ transients by about 150%, whilst increasing the corresponding Ca2+ transients by only 20%. In CCSM preparations that had been pre-contracted with either noradrenaline (0.3 microm) or prostaglandin F(2alpha) (0.1 microm), nerve stimulation inhibited about 70% of the contraction and caused only a 20% decrease in [Ca2+]i. Fluorescent immunohistochemistry with COX-2 antibodies and the reverse transcriptase-polymerase chain reaction (RT-PCR) method showed that the enzyme and its mRNA were highly expressed in the CCSM. These results suggest that spontaneously produced prostaglandins (PGs) not only contribute to the generation of spontaneous contractions but also facilitate nerve-evoked contractions. Conversely, spontaneously released nitric oxide (NO) suppresses excitation. Thus, interaction between spontaneous and neurally mediated regulation of CCSM tone may be fundamental to maintaining the muscle contractility. In addition, both PGs and NO appear to alter CCSM tone with only small changes in [Ca2+]i.

The nitric oxide donor sodium nitroprusside stimulates the Na+-K+ pump in isolated rabbit cardiac myocytes

Nitric oxide (NO) affects the membrane Na(+)-K(+) pump in a tissue-dependent manner. Stimulation of intrinsic pump activity, stimulation secondary to NO-induced Na(+) influx into cells or inhibition has been reported. We used the whole-cell patch clamp technique to measure electrogenic Na(+)-K(+) pump current (I(p)) in rabbit ventricular myocytes. Myocytes were voltage clamped with wide-tipped patch pipettes to achieve optimal perfusion of the intracellular compartment, and I(p) was identified as the shift in holding current induced by 100 microm ouabain. The NO donor sodium nitroprusside (SNP) in concentrations of 1, 10, 50 or 100 microm induced a significant increase in I(p) when the intracellular compartment was perfused with pipette solutions containing 10 mm Na(+), a concentration near physiological levels. SNP had no effect when the pump was near-maximally activated by 80 mm Na(+) in pipette solutions. Stimulation persisted in the absence of extracellular Na(+), indicating its independence of transmembrane Na(+) influx. The SNP-induced pump stimulation was abolished by inhibition of soluble guanylyl cyclase (sGC) with 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one, by inhibition of protein kinase G (PKG) with KT-5823 or by inhibition of protein phosphatase with okadaic acid. Inclusion of the non-hydrolysable cGMP analogue 8pCPT-cGMP, activated recombinant PKG or the sGC-activator YC-1 in patch pipette filling solutions reproduced the SNP-induced pump stimulation. Pump stimulation induced by YC-1 was dependent on the Na(+) concentration but not the K(+) concentration in pipette filling solutions, suggesting an altered sensitivity of the Na(+)-K(+) pump to intracellular Na(+).

L-S-nitrosothiols: endothelium-derived hyperpolarizing factors in porcine coronary arteries?

OBJECTIVE

Bradykinin-induced, endothelium-derived hyperpolarizing factor (EDHF)-mediated responses depend on Ca-dependent K-channels (KCa) of small (SKCa) and intermediate (IKCa) conductance, inwardly rectifying K (KIR) channels and/or Na-K-ATPase. Here we investigated in porcine coronary arteries (PCAs) whether S-nitrosothiols can act as EDHF.

METHODS

Preconstricted PCAs were exposed to bradykinin, the NO donor S-nitroso-N-penicillamine (SNAP), or the S-nitrosothiols L-S-nitrosocysteine (L-SNC), D-SNC and L-S-nitrosoglutathione (L-SNG), with or without KCl, the NO scavenger hydroxocobalamin, the S-nitrosothiol-depleting agent p-hydroxymercurobenzoic acid (PHMBA) and/or inhibitors of NO synthase (L-NAME), guanylyl cyclase (ODQ), SKCa channels (apamin), KCa channels of large conductance (BKCa) (iberiotoxin), IKCa + BKCa channels (charybdotoxin), KIR channels (BaCl2) or Na-K-ATPase (ouabain).

RESULTS

All agonists concentration-dependently relaxed PCAs. L-NAME, charybdotoxin + apamin, KCl, and ouabain shifted the bradykinin concentration-response curve (CRC) approximately 10-fold to the right. BaCl2 did not exert additional effects on top of ouabain. Full blockade of bradykinin was obtained when combining L-NAME with charybdotoxin + apamin, KCl or ouabain + BaCl2. PHMBA reduced the maximum effect of bradykinin. Iberiotoxin + apamin, alone or on top of L-NAME, did not affect bradykinin, SNAP or L-SNC. ODQ and hydroxocobalamin shifted the SNAP, L-SNC, D-SNC, and L-SNG CRCs approximately 10-fold to the right, and, in combination, fully blocked SNAP-induced effects. Charybdotoxin + apamin shifted the L-SNC and L-SNG CRCs, but not the D-SNC or SNAP CRCs, approximately 5-fold to the right. KCl and ouabain (but not BaCl2) shifted the SNAP, L-SNC and L-SNG CRCs 5-10 fold to the right.

CONCLUSIONS

L-S-nitrosothiols activate SKCa + IKCa channels in a stereoselective manner, whereas NO activates Na-K-ATPase. Since S-nitrosothiols decompose to NO, stored L-S-nitrosothiols may mediate bradykinin-induced, EDHF-dependent relaxation.

Role of arginase in the male and female sexual arousal response

The NO-cGMP pathway plays a key role in the male and female genital sexual arousal response. Nitric oxide synthase (NOS) utilizes L-arginine and oxygen as substrates to produce nitric oxide (NO) and citrulline. Arginase is a metalloenzyme that catalyzes the hydrolysis of L-arginine to produce L-ornithine and urea. It is proposed that arginase competes for L-arginine and reduces NOS activity in genital tissues, thus modulating sexual function. Using 2 transition state analogue inhibitors of arginase, 2(S)-Amino-6-boronohexanoic acid (ABH) and S-(2-boronoethyl)-L-cysteine (BEC), we have characterized arginase activity in penile and vaginal tissue. Neither of these inhibitors has activity against NOS. Thus, ABH and BEC are useful compounds for examining the role of arginase in genital tissue physiology, without directly influencing NOS activity. We present data to suggest that arginase may regulate NO production by competing for endogenous pools of L-arginine. In this fashion, arginase is an indirect regulator of penile and vaginal blood flow and specific arginase inhibitors may improve genital blood flow during sexual arousal. As evidenced by the upregulation of arginase in specific disease states, its distribution in the vagina, and its modulation by sex steroid hormones, this enzyme may also participate in numerous other physiological and pathophysiological processes, such as tissue growth, fibrosis, and immune function.

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.

Mediators of bradykinin-induced vasorelaxation in human coronary microarteries

To investigate the mediators of bradykinin-induced vasorelaxation in human coronary microarteries (HCMAs), HCMAs (diameter approximately 300 microm) obtained from 42 heart valve donors (20 men and 22 women; age range, 3 to 65 years; mean age, 46 years) were mounted in Mulvany myographs. In the presence of the cyclooxygenase inhibitor indomethacin, bradykinin relaxed preconstricted HCMAs in a concentration-dependent manner. N(G)-nitro-L-arginine methyl ester and ODQ (inhibitors of nitric oxide [NO] synthase and guanylyl cyclase, respectively) and the NO scavenger hydroxocobalamin, either alone or in combination, shifted the bradykinin concentration-response curve to the right. Removal of H2O2 (with catalase), inhibition of cytochrome P450 epoxygenase (with sulfaphenazole or clotrimazole) or gap junctions (with 18alpha-glycyrrhetinic acid or carbenoxolone), and blockade of large- (BK(Ca)) and small- (SK(Ca)) conductance Ca2+-dependent K+ channels (with iberiotoxin and apamin), either alone or in addition to hydroxocobalamin, did not affect bradykinin. In contrast, complete blockade of bradykinin-induced relaxation was obtained when we combined the nonselective BK(Ca) and intermediate-conductance (IK(Ca)) Ca2+-dependent K+ channel blocker charybdotoxin and apamin with hydroxocobalamin. Charybdotoxin plus apamin alone were without effect. Inhibition of inwardly rectifying K+ channels (K(IR)) and Na+/K+-ATPase (with BaCl2 and ouabain, respectively) shifted the bradykinin concentration-response curve 10-fold to the right but did not exert an additional effect in the presence of hydroxocobalamin. In conclusion, bradykinin-induced relaxation in HCMAs depends on (1) the activation of guanylyl cyclase, K(IR), and Na(+)/K(+)-ATPase by NO and (2) IK(Ca) and SK(Ca) channels. The latter are activated by a factor other than NO. This factor is not a cytochrome P450 epoxygenase product or H2O2, nor does it depend on gap junctions or BK(Ca) channels.

Evaluation of potassium ion as the endothelium-derived hyperpolarizing factor (EDHF) in the bovine coronary artery

1. This study explored the role of the potassium ion in endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine coronary artery. 2. Bradykinin-induced, EDHF-mediated vasodilatation was blocked by the Na(+)-K(+) ATPase inhibitor, ouabain (1 micro M), in a time-dependent manner, with maximal blockade seen after 90 min. In contrast, the K(IR) channel inhibitor, Ba(2+) (30 micro M), had no effect. 3. When the potassium content of the bathing solution was increased in a single step from 5.9 to 7-19 mM, powerful vasodilatation (max. 75.9+/-3.6%) was observed. Vasodilatation was transient and, consequently, cumulative addition of potassium produced little vasodilatation, with vasoconstriction predominating at the higher concentrations. 4. The magnitude of potassium-induced vasodilatation was similar in endothelium-containing and endothelium-denuded rings, and was unaffected by Ba(2+) (30 micro M), but abolished by ouabain (1 micro M). 5. Ouabain (1 micro M, 90 min) powerfully blocked bradykinin-induced, nitric oxide-mediated vasodilatation as well as that induced by the nitrovasodilator, glyceryl trinitrate, but that induced by the K(ATP) channel opener, levcromakalim, was hardly affected. 6. Thus, activation of Na(+)-K(+) ATPase is likely to be involved in the vasodilator responses of the bovine coronary artery to both nitric oxide and EDHF. These findings, together with the ability of potassium to induce powerful, ouabain- but not Ba(2+)-sensitive, endothelium-independent vasodilatation, are consistent with this ion contributing to the EDHF response in this tissue.

Reactive oxygen nitrogen species decrease cystic fibrosis transmembrane conductance regulator expression and cAMP-mediated Cl- secretion in airway epithelia

We investigated putative mechanisms by which nitric oxide modulates cystic fibrosis transmembrane conductance regulator (CFTR) expression and function in epithelial cells. Immunoprecipitation followed by Western blotting, as well as immunocytochemical and cell surface biotinylation measurements, showed that incubation of both stably transduced (HeLa) and endogenous CFTR expressing (16HBE14o-, Calu-3, and mouse tracheal epithelial) cells with 100 microm diethylenetriamine NONOate (DETA NONOate) for 24-96 h decreased both intracellular and apical CFTR levels. Calu-3 and mouse tracheal epithelial cells, incubated with DETA NONOate but not with 100 microm 8-bromo-cGMP for 96 h, exhibited reduced cAMP-activated short circuit currents when mounted in Ussing chambers. Exposure of Calu-3 cells to nitric oxide donors resulted in the nitration of a number of proteins including CFTR. Nitration was augmented by proteasome inhibition, suggesting a role for the proteasome in the degradation of nitrated proteins. Our studies demonstrate that levels of nitric oxide that are likely to be encountered in the vicinity of airway cells during inflammation may nitrate CFTR resulting in enhanced degradation and decreased function. Decreased levels and function of normal CFTR may account for some of the cystic fibrosis-like symptoms that occur in chronic inflammatory lung diseases associated with increased NO production.

Lack of nitric oxide synthase depresses ion transporting enzyme function in cardiac muscle

Nitric oxide (NO*) is produced endogenously from NOS isoforms bound to sarcolemmal (SL) and sarcoplasmic reticulum (SR) membranes. To investigate whether locally generated NO* directly affects the activity of enzymes mediating ion active transport, we studied whether knockout of selected NOS isoforms would affect the functions of cardiac SL (Na+ + K+)-ATPase and SR Ca2+-ATPase. Cardiac SL and SR vesicles containing either SL (Na+ + K+)-ATPase or SR Ca2+-ATPase were isolated from mice lacking either nNOS or eNOS, or both, and tested for enzyme activities. Western blot analysis revealed that absence of single or double NOS isoforms did not interrupt the protein expression of SL (Na+ + K+)-ATPase and SR Ca2+-ATPase in cardiac muscle cells. However, lack of NOS isoforms in cardiac muscle significantly altered both (Na+ + K+)-ATPase activity and SR Ca2+-ATPase function. Our experimental results suggest that disrupted endogenous NO* production may change local redox conditions and lead to an unbalanced free radical homeostasis in cardiac muscle cells which, in turn, may affect key enzyme activities and membrane ion active transport systems in the heart.

Interactions between drugs for erectile dysfunction and drugs for cardiovascular disease

The association of erectile dysfunction (ED) and cardiovascular disease is well-documented in the literature and both conditions share risk factors. Therefore, it is difficult to distinguish the effect of underlying disease and adverse effects of the drugs and/or interactions between ED drugs and drugs implemented for cardiovascular disease. The known interactions of systemic administered drugs for ED with drugs for cardiovascular disease are mainly pharmacodynamic. Thus, nitrates enhance the production of cyclic GMP and combined with phosphodiesterase type-5 inhibitors this can lead to severe hypotension. The same is the case for the treatment with phentolamine in patients treated with beta-adrenoceptor antagonists. Due to increased partial thromboplastin time, the risk of bleeding is enhanced for intracavernous alprostadil injection in heparin-treated patients. Pharmacokinetic interactions of clinical importance have been described for ED drugs with other therapeutic groups such as sildenafil with the antifungal drug, ketoconazole, and apomorphine with the antiparkinson drug, entacapon. Although sildenafil and antihypertensive dihydropyridines like amlodipine are metabolized by the same cytochrome P450 enzyme, CYP3A4 in the liver, the combination of these drugs does not exhibit a synergistic blood pressure lowering action. Unfortunately documentation concerning drug interactions is often poor and occasional.

Cellular mechanisms of nitric oxide-induced relaxation of corporeal smooth muscle in the guinea-pig

The cellular mechanism of nitric oxide (NO)-induced relaxation in corporeal smooth muscle (CSM) of the guinea-pig was investigated. Changes in the intracellular concentration of calcium ions ([Ca(2+)](i)), membrane potential and isometric tension were measured. CSM cells exhibited spontaneous depolarizations and transient increases in [Ca(2+)](i) (Ca(2+) transients) which were accompanied by contractions. This spontaneous activity was abolished by nifedipine (10 microM). NO released by 3-morpholino-sydnonimine (SIN-1, 10 microM) hyperpolarized the membrane and prevented the generation of spontaneous depolarizations. SIN-1 also abolished Ca(2+) transients and associated contractions. These effects of SIN-1 were blocked by 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10 microM), an inhibitor of guanylate cyclase. Noradrenaline (NA, 1 microM) increased [Ca(2+)](i) to levels similar to those produced by high potassium-containing solution (high K(+) solution, [K(+)](o) = 40 mM), however, NA-induced contractions were three times greater in amplitude than those induced by high K(+) solution. In NA precontracted preparations, SIN-1 inhibited 80 % of the contraction and decreased [Ca(2+)](i) by 20 %. In contrast, nifedipine reduced [Ca(2+)](i) by 80 %, while the level of contraction was decreased by only 20 %. SIN-1-induced reduction in [Ca(2+)](i) but not the tension effect, was abolished by pretreatment with cyclopiazonic acid (CPA, 10 microM). In high K(+) precontracted preparations, SIN-1 inhibited 80 % of the contraction and reduced [Ca(2+)](i) by 20 %. Nifedipine, however, largely abolished increases in both [Ca(2+)](i) and tension under these circumstances. These results suggest that decreasing the sensitivity of contractile proteins to Ca(2+) is probably the key mechanism of NO-induced relaxation in CSM of the guinea-pig.

Lack of amiloride-sensitive transport across alveolar and respiratory epithelium of iNOS(-/-) mice in vivo

The extent to which endogenously generated nitric oxide alters Na(+) transport across the mammalian alveolar epithelium in vivo has not been documented. Herein we measured alveolar fluid clearance and nasal potential differences in mice lacking the inducible form of nitric oxide synthase [iNOS; iNOS(-/-)] and their corresponding wild-type controls [iNOS(+/+)]. Alveolar fluid clearance values in iNOS(+/+) and iNOS(-/-) anesthetized mice with normal oxygenation and acid-base balance were ~30% of instilled fluid/30 min. In both groups of mice, fluid absorption was dependent on vectorial Na(+) movement. Amiloride (1.5 mM) decreased alveolar fluid clearance in iNOS(+/+) mice by 61%, whereas forskolin (50 microM) increased alveolar fluid clearance by 55% by stimulating amiloride-insensitive pathways. Neither agent altered alveolar fluid clearance in iNOS(-/-) mice. Hyperoxia upregulated iNOS expression in iNOS(+/+) mice and decreased their amiloride-sensitive component of alveolar fluid clearance but had no effect on the corresponding values in iNOS(-/-) mice. Nasal potential difference measurements were consistent with alveolar fluid clearance in that both groups of mice had similar baseline values, which were amiloride sensitive in the iNOS(+/+) but not in the iNOS(-/-) mice. These data suggest that nitric oxide produced by iNOS under basal conditions plays an important role in regulating amiloride-sensitive Na(+) channels in alveolar and airway epithelia.

Pharmacotherapy for erectile dysfunction

Erectile dysfunction (ED) is defined as the consistent inability to obtain or maintain an erection for satisfactory sexual relations. An estimated 20-30 million men suffer from some degree of sexual dysfunction. The past 20 years of research on erectile physiology have increased our understanding of the biochemical factors and intracellular mechanisms responsible for corpus cavernosal smooth muscle contraction and relaxation, and revealed that ED is predominantly a disease of vascular origin. Since the advent of sildenafil (Viagra), there has been a resurgence of interest in ED, and an increase in patients presenting with this disease. A thorough knowledge of the physiology of erection is essential for future pharmacological innovations in the field of male ED.

The role of nitric oxide in the regulation of ion channels in airway epithelium: implications for diseases of the lung

The human respiratory tract is covered with airway surface liquid (ASL) that is essential for lung defense and normal airway function. The quantity and composition of ASL is regulated by active ion transport across the airway epithelium. Abnormal electrolyte transport produces changes in ASL volume and composition, inhibits mucociliary clearance and leads to chronic infection of airway surfaces, as is evident in cystic fibrosis. Agonists that induce intracellular increases in cAMP or Ca2+ are generally associated with electrolyte secretion. While these mechanisms have been studied in detail for many years, modulation of ion channels by nitric oxide (NO) has emerged only recently as a significant determinant of ion channel function. NO is a physiological regulator of transepithelial ion movement and alterations of its generation and action may play an important role in the pathogenesis of lung disorders characterized by hypersecretion of ASL. This review presents the current understanding of regulation of airway epithelial ion channels by NO and attempts to highlight the importance of this regulation for lung defense.

A standardized procedure for using human corpus cavernosum strips to evaluate drug activity

The main problem of using human corpus cavernosum (HCC) tissue to perform bioassay is linked to its limited availability further complicated by the heterogeneous source of the tissues used. Here, we show that gender reassignment is a reliable source of human tissue without major ethical problems. Indeed, the entire corpus cavernosum is obtained from the surgery procedure, which allows creating a standardized procedure to prepare HCC strip. In addition, human tissue, if kept in the fridge in the condition described, does not loose its ability to contract to phenylephrine (PE; alpha agonist), angiotensin II (AG II) and KCl up to 4 days. Furthermore, once contracted with PE, HCC relaxes to acetylcholine (endothelium-dependent mechanism); sodium nitroprusside (endothelium-independent mechanism); cromakalim (CRK), a K(ATP) channel opener; or alprostadil, a synthetic PGE2 (ALPR). In conclusion, we have standardized a procedure that allows the use of HCC strips to evaluate drug activity and/or to study pathophysiological mechanisms with an intact functional human tissue up to 4 days from the surgery procedure.

Mechanisms of sodium pump regulation

The Na(+)-K(+)-ATPase, or sodium pump, is the membrane-bound enzyme that maintains the Na(+) and K(+) gradients across the plasma membrane of animal cells. Because of its importance in many basic and specialized cellular functions, this enzyme must be able to adapt to changing cellular and physiological stimuli. This review presents an overview of the many mechanisms in place to regulate sodium pump activity in a tissue-specific manner. These mechanisms include regulation by substrates, membrane-associated components such as cytoskeletal elements and the gamma-subunit, and circulating endogenous inhibitors as well as a variety of hormones, including corticosteroids, peptide hormones, and catecholamines. In addition, the review considers the effects of a range of specific intracellular signaling pathways involved in the regulation of pump activity and subcellular distribution, with particular consideration given to the effects of protein kinases and phosphatases.

Nitric oxide and peroxynitrite anion modulate liver plasma membrane fluidity and Na(+)/K(+)-ATPase activity

Free radicals attack membranes and frequently alter their fluidity and function. The aim of the present work was to study the effect of nitric oxide (NO) radical and peroxynitrite anion on basolateral liver plasma membrane fluidity and on the activity of Na(+)/K(+)-ATPase. Basolateral membranes (BM) were isolated by ultracentrifugation in sucrose gradients and characterized enzymatically. BM were incubated with SNAP (a NO donor) or SIN-1 (a peroxynitrite donor). The release of NO or peroxynitrite was monitored by measuring NO(-)(2) + NO(-)(3). Relative fluidity was measured by polarization of fluorescence. NO increased membrane fluidity while peroxynitrite decreased it in a concentration-dependent manner. Na(+)/K(+)-ATPase activity was reduced by NO or peroxynitrite. Peroxynitrite anion inhibits ATPase activity in part by decreasing fluidity. However, it is very likely that both compounds inhibit ATPase activity by oxidation of the thiol groups of the enzyme. Our results suggest that NO may exert part of its biological effects by modulating membrane fluidity and function.

Neuroeffector transmission to different layers of smooth muscle in the rat penile bulb

1. Using intracellular recording techniques, two distinct layers of smooth muscle were identified in the rat penile bulb. The inner muscle layer (parenchyma) exhibited spontaneous action potentials, while the outer sheet (sac) was electrically quiescent. 2. In the parenchyma, transmural stimulation initiated non-adrenergic, non-cholinergic (NANC) inhibitory junction potentials (IJPs) which were abolished by Nomeganitro-L-arginine (LNA) or 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The amplitude of IJPs was reduced by ouabain, dinitrophenol or decreasing the extracellular potassium concentration ([K+]o) but not by several K+ channel blockers. 3. The parenchyma also received an excitatory innervation mediated by alpha-adrenoceptors which caused a contraction that was not associated with a membrane potential change. 4. In the sac, transmural stimulation initiated two component excitatory junction potentials (EJPs) mediated by alpha-adrenoceptors and associated action potentials. The initial component was more dramatically suppressed than the secondary component by caffeine, ryanodine or cyclopiazonic acid (CPA). Lowering of the extracellular chloride concentration ([Cl-]o) selectively inhibited the rapid component of EJPs, while niflumic acid was less potent. 5. These results suggest that IJPs in the parenchyma result from the release of NO which stimulates sodium pump activity following the activation of guanylate cyclase. In the sac, the activation of alpha-adrenoceptors initiates EJPs by releasing Ca2+ from intracellular stores which activates Ca2+-activated channels.

Changes of sodium and ATP affinities of the cardiac (Na,K)-ATPase during and after nitric oxide deficient hypertension

In the cardiovascular system, NO is involved in the regulation of a variety of functions. Inhibition of NO synthesis induces sustained hypertension. In several models of hypertension, elevation of intracellular sodium level was documented in cardiac tissue. To assess the molecular basis of disturbances in transmembraneous transport of Na+, we studied the response of cardiac (Na,K)-ATPase to NO-deficient hypertension induced in rats by NO-synthase inhibition with 40 mg/kg/day N(G)-nitro-L-arginine methyl ester (L-NAME) for 4 four weeks. After 4-week administration of L-NAME, the systolic blood pressure (SBP) increased by 36%. Two weeks after terminating the treatment, the SBP recovered to control value. When activating the (Na,K)-ATPase with its substrate ATP, no changes in Km and Vmax values were observed in NO-deficient rats. During activation with Na+, the Vmax remained unchanged, however the K(Na) increased by 50%, indicating a profound decrease in the affinity of the Na+-binding site in NO-deficient rats. After recovery from hypertension, the activity of (Na,K)-ATPase increased, due to higher affinity of the ATP-binding site, as revealed from the lowered Km value for ATP. The K(Na) value for Na+ returned to control value. Inhibition of NO-synthase induced a reversible hypertension accompanied by depressed Na+-extrusion from cardiac cells as a consequence of deteriorated Na+-binding properties of the (Na,K)-ATPase. After recovery of blood pressure to control values, the extrusion of Na+ from cardiac cells was normalized, as revealed by restoration of the (Na,K)-ATPase activity.

Nitric oxide reduces the molecular activity of Na+,K+-ATPase in opossum kidney cells

BACKGROUND

Nitric oxide (NO) directly inhibits fluid and solute reabsorption in the proximal tubule. In the present study, we investigated the effect of NO on the Na+, K+-ATPase of opossum kidney (OK) cells, a proximal tubule cell line, and its mechanisms.

METHODS

Na+,K+-ATPase activity in the membrane fraction of OK cells was measured as the ouabain-sensitive ATP hydrolytic activity. The enzyme unit number on intact cells was measured by ouabain-binding assay.

RESULTS

Incubation with 0.5 mM sodium nitroprusside (SNP), a NO donor, for two hours inhibited the catalytic activity of the membrane-associated Na+,K+-ATPase in OK cells to 65.5 +/- 9.7% of control (N = 6, P < 0.05 vs. control). This effect of SNP was concentration- and time-dependent. The NO scavenger hemoglobin blunted, while another NO donor spermine NONOate (5 microM) mimicked this effect of SNP. At all concentrations and time points tested, SNP did not alter the molecular number of Na+,K+-ATPase on intact OK cells, indicating that NO inhibited the molecular activity of Na+,K+-ATPase. The soluble guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one (ODQ), blunted the inhibitory effect of SNP on the Na+,K+-ATPase activity. An exogenous cGMP analog similarly inhibited the Na+,K+-ATPase activity. Neither lipid soluble antioxidants vitamin E/probucol or thiol group compound DL-dithiothreitol (DTT) altered the inhibitory effect of SNP on the Na+,K+-ATPase activity.

CONCLUSIONS

NO inhibited the molecular activity of the Na+,K+-ATPase of the OK proximal tubule cell line probably via cGMP-dependent mechanisms.