Endogenous testosterone increases L-type Ca2+ channel expression in porcine coronary smooth muscle

Sexually dimorphic mechanisms of H2O2-mediated dilation in porcine coronary arterioles with ischemia and endurance exercise training

We determined the impact of sex on H2O2-mediated dilation in coronary arterioles and the contribution of K+ channels after exercise training in ischemic heart disease. We hypothesized that arterioles from male and female swine would similarly display impaired H2O2-induced dilation after chronic occlusion that would be corrected by exercise training. Yucatan miniswine were surgically instrumented with an ameroid constrictor around the proximal left circumflex artery, gradually inducing occlusion and a collateral-dependent myocardium. Arterioles from the left anterior descending artery myocardial region served as nonoccluded controls. Eight weeks postoperatively, swine of each sex were separated into sedentary and exercise-trained (progressive treadmill regimen; 5 days/wk for 14 wk) groups. Collateral-dependent arterioles of sedentary female pigs displayed impaired sensitivity to H2O2 that was reversed with exercise training. In contrast, male pigs exhibited enhanced sensitivity to H2O2 in collateral-dependent versus nonoccluded arterioles in both sedentary and exercise-trained groups. Large-conductance, calcium-dependent K+ (BKCa) and 4-aminopyridine (AP)-sensitive voltage-gated K+ (Kv) channels contributed to H2O2-mediated dilation in nonoccluded and collateral-dependent arterioles of exercise-trained females, but not in arterioles of sedentary female or sedentary or exercise-trained male swine. BKCa channel, protein kinase A (PKA), and protein kinase G (PKG) protein levels were not significantly different between groups, nor were kinase enzymatic activities. Taken together, our studies suggest that in female swine, exercise training stimulates the coupling of H2O2 signaling with BKCa and 4-AP-sensitive Kv channels, compensating for impaired dilation in collateral-dependent arterioles. Interestingly, coronary arterioles from neither sedentary female or male swine, regardless of training status, depended upon BKCa or 4-AP-sensitive Kv channels for H2O2-mediated dilation.NEW & NOTEWORTHY The current studies reveal sexually dimorphic adaptations to H2O2-mediated dilation, and unique contributions of K+ channels, in coronary arterioles from swine subjected to chronic ischemia and exercise training; findings important for development of therapeutic strategies. In female swine, chronic ischemia attenuates dilation, which is reversed by exercise training via BKCa and Kv channel stimulation. In male swine, ischemia enhances dilation to H2O2, which is further augmented by exercise training and independent of BKCa and Kv channels.

Interaction of sex hormone receptors and calcium handling proteins in the left ventricle of patients with heart failure

Heart failure (HF) is one of the leading causes of death from cardiovascular disease among adults worldwide. The role of sex hormone receptors in the pathogenesis of HF and their regulatory mechanisms remain unclear. This study focused on investigating the localization and expression of sex hormone receptors (ERα, ERβ, AR and PR) and calcium handling proteins (SERCA2a and Cav1.2) in the left ventricle (LV) tissues of patients with HF, and to investigate their interactions. The LV tissues of HF patients were collected, and the localization of sex hormone receptors and calcium handling proteins was detected by immunofluorescence and immunohistochemistry. Western blotting was performed to study the expression levels of sex hormone receptors and calcium handling proteins. The interactions between these proteins were identified by immunofluorescence co-location and immunoprecipitation respectively. Compared with the control group, the expression levels of sex hormone receptors and calcium handling proteins in HF patients were significantly decreased. There was co-localization and interaction between protein ERα and Cav1.2, protein AR and SERCA2a, respectively. In summary, sex hormone receptors may be involved in regulating the progression of HF by interacting with calcium handling proteins.

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Testosterone therapy and cardiovascular diseases

Since it was first synthesised in 1935, testosterone (T) has been viewed as the mythical Fountain of Youth, promising rejuvenation, restoring sexual appetites, growing stronger muscles, and quicker thinking. T is endowed with direct effects on myocardial and vascular structure and function, as well as on risk factors for cardiovascular (CV) disease. Indeed, low serum T levels are a risk factor for diabetes, metabolic syndrome, inflammation, and dyslipidaemia. Moreover, many studies have shown that T deficiency per se is an independent risk factor of CV and all-cause mortality. On this background and due to direct-to-patient marketing by drug companies, we have witnessed to the widespread use of T replacement therapy (TT) without clear indications particularly in late-life onset hypogonadism. The current review will dwell upon current evidence and controversies surrounding the role of T in the pathophysiology of CV diseases, the link between circulating T levels and CV risk, and the use of replacing T as a possible adjuvant treatment in specific CV disorders. Specifically, recent findings suggest that heart failure and type 2 diabetes mellitus represent two potential targets of T therapy once that a state of hypogonadism is diagnosed. However, only if ongoing studies solve the CV safety issue the T orchid may eventually 'bloom'.

Blockade of Acid-Sensing Ion Channels Increases Urinary Bladder Capacity With or Without Intravesical Irritation in Mice

We conducted this study to examine whether acid-sensing ion channels (ASICs) are involved in the modulation of urinary bladder activity with or without intravesical irritation induced by acetic acid. All in vivo evaluations were conducted during continuous infusion cystometry in decerebrated unanesthetized female mice. During cystometry with a pH 6.3 saline infusion, an i.p. injection of 30 μmol/kg A-317567 (a potent, non-amiloride ASIC blocker) increased the intercontraction interval (ICI) by 30% (P < 0.001), whereas vehicle injection had no effect. An intravesical acetic acid (pH 3.0) infusion induced bladder hyperactivity, with reductions in ICI and maximal voiding pressure (MVP) by 79% (P < 0.0001) and 29% (P < 0.001), respectively. A-317567 (30 μmol/kg i.p.) alleviated hyperreflexia by increasing the acid-shortened ICI by 76% (P < 0.001). This dose produced no effect on MVP under either intravesical pH condition. Further analysis in comparison with vehicle showed that the increase in ICI (or bladder capacity) by the drug was not dependent on bladder compliance. Meanwhile, intravesical perfusion of A-317567 (100 μM) had no effect on bladder activity during pH 6.0 saline infusion cystometry, and drug perfusion at neither 100 μM nor 1 mM produced any effects on bladder hyperreflexia during pH 3.0 acetic acid infusion cystometry. A-317567 has been suggested to display extremely poor penetrability into the central nervous system and thus to be a peripherally active blocker. Taken together, our results suggest that blockade of ASIC signal transduction increases bladder capacity under normal intravesical pH conditions and alleviates bladder hyperreflexia induced by intravesical acidification and that the site responsible for this action is likely to be the dorsal root ganglia.

Androgen Affects the Dynamics of Intrinsic Plasticity of Pyramidal Neurons in the CA1 Hippocampal Subfield in Adolescent Male Rats

Androgen receptor (AR) is abundantly expressed in the preoptico-hypothalamic area, bed nucleus of stria terminalis, and medial amygdala of the brain where androgen plays an important role in regulating male sociosexual, emotional and aggressive behaviors. In addition to these brain regions, AR is also highly expressed in the hippocampus, suggesting that the hippocampus is another major target of androgenic modulation. It is known that androgen can modulate synaptic plasticity in the CA1 hippocampal subfield. However, to date, the effects of androgen on the intrinsic plasticity of hippocampal neurons have not been clearly elucidated. In this study, the effects of androgen on the expression of AR in the hippocampus and on the dynamics of intrinsic plasticity of CA1 pyramidal neurons were examined using immunohistochemistry, Western blotting and whole-cell current-clamp recording in unoperated, sham-operated, orchiectomized (OCX), OCX + testosterone (T) or OCX + dihydrotestosterone (DHT)-primed adolescent male rats. Orchiectomy significantly decreased AR-immunoreactivity, resting membrane potential, action potential numbers, afterhyperpolarization amplitude and membrane resistance, whereas it significantly increased action potential threshold and membrane capacitance. These effects were successfully reversed by treatment with either aromatizable androgen T or non-aromatizable androgen DHT. Furthermore, administration of the AR-antagonist flutamide in intact rats showed similar changes to those in OCX rats, suggesting that androgens affect the excitability of CA1 pyramidal neurons possibly by acting on the AR. Our current study potentially clarifies the role of androgen in enhancing the basal excitability of the CA1 pyramidal neurons, which may influence selective neuronal excitation/activation to modulate certain hippocampal functions.

Hypogonadism and its treatment following ischaemic stroke in men with type 2 diabetes mellitus

Premature mortality in Russia is a major socio-economic problem, especially from acute cerebrovascular diseases which constitute 21.4% of the total mortality and is a considerable contributor to chronic disability. Risk of vascular catastrophe is higher in males than females, thought, in part, due to anti-atherosclerotic effects of oestrogens in females whilst an associated age-related deficiency of testosterone is observed in men. Clinical symptoms such as high blood pressure, changes in lipid profile, insulin resistance, obesity, and blood coagulation factors often accompany declining testosterone in males and reduced total testosterone is considered a cardiovascular risk factor. In the present study, the prevalence of hypogonadism in men who had suffered ischaemic stroke was evaluated along with the efficacy of testosterone undecanoate injections (TU) in patients with testosterone deficiency and type-2 diabetes (T2DM) in the acute phase of hemispheric ischaemic stroke. Hypogonadism was present in 66.3% of patients with ischaemic stroke, 50% with T2DM, and 26.3% without T2DM, respectively. TU treatment, at both the 2 and 5-year observation points, demonstrated significant improvements in biochemical, physical, and mental parameters. This supports that testosterone deficiency is a contributing factor in ischaemic events and that long-term testosterone therapy could play an important role in patient recovery.

Reciprocality Between Estrogen Biology and Calcium Signaling in the Cardiovascular System

17β-Estradiol (E₂) is the main estrogenic hormone in the body and exerts many cardiovascular protective effects. Via three receptors known to date, including estrogen receptors α (ERα) and β (ERβ) and the G protein-coupled estrogen receptor 1 (GPER, aka GPR30), E₂ regulates numerous calcium-dependent activities in cardiovascular tissues. Nevertheless, effects of E₂ and its receptors on components of the calcium signaling machinery (CSM), the underlying mechanisms, and the linked functional impact are only beginning to be elucidated. A picture is emerging of the reciprocality between estrogen biology and Ca²⁺ signaling. Therein, E₂ and GPER, via both E₂-dependent and E₂-independent actions, moderate Ca²⁺-dependent activities; in turn, ERα and GPER are regulated by Ca²⁺ at the receptor level and downstream signaling via a feedforward loop. This article reviews current understanding of the effects of E₂ and its receptors on the cardiovascular CSM and vice versa with a focus on mechanisms and combined functional impact. An overview of the main CSM components in cardiovascular tissues will be first provided, followed by a brief review of estrogen receptors and their Ca²⁺-dependent regulation. The effects of estrogenic agonists to stimulate acute Ca²⁺ signals will then be reviewed. Subsequently, E₂-dependent and E₂-independent effects of GPER on components of the Ca²⁺ signals triggered by other stimuli will be discussed. Finally, a case study will illustrate how the many mechanisms are coordinated to moderate Ca²⁺-dependent activities in the cardiovascular system.

Sex differences in the vascular function and related mechanisms: role of 17β-estradiol

The incidence of cardiovascular disease (CVD) is lower in premenopausal women but increases with age and menopause compared with similarly aged men. Based on the prevalence of CVD in postmenopausal women, sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the protection from CVD in premenopausal women. Recent Women’s Health Initiative studies, Cochrane Review studies, the Early Versus Late Intervention Trial with Estradiol Study, and the Kronos Early Estrogen Prevention Study have suggested that beneficial effects of hormone replacement therapy (HRT) are seen in women of <60 yr of age and if initiated within <10 yr of menopause. In contrast, the beneficial effects of HRT are not seen in women of >60 yr of age and if commenced after 10 yr of menopause. The higher incidence of CVD and the failure of HRT in postmenopausal aged women could be partly associated with fundamental differences in the vascular structure and function between men and women and in between pre- and postmenopausal women, respectively. In this regard, previous studies from human and animal studies have identified several sex differences in vascular function and associated mechanisms. The female sex hormone 17β-estradiol regulates the majority of these mechanisms. In this review, we summarize the sex differences in vascular structure, myogenic properties, endothelium-dependent and -independent mechanisms, and the role of 17β-estradiol in the regulation of vascular function.

17β-estradiol reduces Cav 1.2 channel abundance and attenuates Ca2+ -dependent contractions in coronary arteries

One mechanism by which the female sex may protect against elevated coronary vascular tone is inhibition of Ca²⁺ entry into arterial smooth muscle cells (ASMCs). In vitro findings confirm that high estrogen concentrations directly inhibit voltage‐dependent Ca_v1.2 channels in coronary ASMCs. For this study, we hypothesized that the nonacute, in vitro exposure of coronary arteries to a low concentration of 17β‐estradiol (17βE) reduces the expression of Ca_v1.2 channel proteins in coronary ASMCs. Segments of the right coronary artery obtained from sexually mature female pigs were mounted for isometric tension recording. As expected, our results indicate that high concentrations (≥10 μmol/L) of 17βE acutely attenuated Ca²⁺‐dependent contractions to depolarizing KCl stimuli. Interestingly, culturing coronary arteries for 24 h in a 10,000‐fold lower concentration (1 nmol/L) of 17βE also attenuated KCl‐induced contractions and reduced the contractile response to the Ca_v1.2 agonist, FPL64176, by 50%. Western blots revealed that 1 nmol/L 17βE decreased protein expression of the pore‐forming α_1C subunit (Ca_vα) of the Ca_v1.2 channel by 35%; this response did not depend on an intact endothelium. The 17βE‐induced loss of Ca_vα protein in coronary arteries was prevented by the estrogen ERα/ERβ antagonist, ICI 182,780, whereas the GPER antagonist, G15, did not prevent it. There was no effect of 1 nmol/L 17βE on Ca_vα transcript expression. We conclude that 17βE reduces Ca_v1.2 channel abundance in isolated coronary arteries by a posttranscriptional process. This unrecognized effect of estrogen may confer physiological protection against the development of abnormal Ca²⁺‐dependent coronary vascular tone.

Altered ionic currents and amelioration by IGF-1 and PACAP in motoneuron-derived cells modelling SBMA

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a motor neuron disease caused by the expansion of a polymorphic CAG tandem repeat encoding a polyglutamine (polyQ) tract in the androgen receptor (AR) gene. SBMA is triggered by the binding of mutant AR to its natural ligands, testosterone and dihydrotestosterone (DHT). To investigate the neuronal alterations of motor neuron cell models of SBMA, we applied patch-clamp methods to verify how polyQ expansions in the AR alter cell ionic currents. We used mouse motoneuron-derived MN-1 cells expressing normal AR (MN24Q) and mutant AR (MN100Q treated cells with vehicle EtOH and DHT). We observed a reduction of the current flux mainly at depolarizing potentials in the DHT-treated cells, while the dissection of macroscopic currents showed single different cationic currents belonging to voltage-gated channels. Also, we treated the cells with IGF-1 and PACAP, which have previously been shown to protect MN-1 cells from the toxicity of mutant AR, and we found an amelioration of the altered currents. Our results suggest that the electrophysiological correlate of SBMA is a suitable reference point for the identification of disease symptoms and for future therapeutic targets.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

CaV1.2/CaV3.x channels mediate divergent vasomotor responses in human cerebral arteries

The regulation of arterial tone is critical in the spatial and temporal control of cerebral blood flow. Voltage-gated Ca(2+) (CaV) channels are key regulators of excitation-contraction coupling in arterial smooth muscle, and thereby of arterial tone. Although L- and T-type CaV channels have been identified in rodent smooth muscle, little is known about the expression and function of specific CaV subtypes in human arteries. Here, we determined which CaV subtypes are present in human cerebral arteries and defined their roles in determining arterial tone. Quantitative polymerase chain reaction and Western blot analysis, respectively, identified mRNA and protein for L- and T-type channels in smooth muscle of cerebral arteries harvested from patients undergoing resection surgery. Analogous to rodents, CaV1.2 (L-type) and CaV3.2 (T-type) α1 subunits were expressed in human cerebral arterial smooth muscle; intriguingly, the CaV3.1 (T-type) subtype present in rodents was replaced with a different T-type isoform, CaV3.3, in humans. Using established pharmacological and electrophysiological tools, we separated and characterized the unique profiles of Ca(2+) channel subtypes. Pressurized vessel myography identified a key role for CaV1.2 and CaV3.3 channels in mediating cerebral arterial constriction, with the former and latter predominating at higher and lower intraluminal pressures, respectively. In contrast, CaV3.2 antagonized arterial tone through downstream regulation of the large-conductance Ca(2+)-activated K(+) channel. Computational analysis indicated that each Ca(2+) channel subtype will uniquely contribute to the dynamic regulation of cerebral blood flow. In conclusion, this study documents the expression of three distinct Ca(2+) channel subtypes in human cerebral arteries and further shows how they act together to orchestrate arterial tone.

5α-Dihydrotestosterone regulates the expression of L-type calcium channels and calcium-binding protein regucalcin in human breast cancer cells with suppression of cell growth

Androgens have been associated with the development of normal breast, and their role in mammary gland carcinogenesis has also been described. Several studies reported that androgens inhibit breast cancer cell growth, whereas others linked their action with the modulation of calcium (Ca(2+)) pumps, Ca(2+) channels and Ca(2+)-binding proteins. Also, it is known that deregulated Ca(2+) homeostasis has been implicated in the pathophysiology of breast. The L-type Ca(2+) channels (LTCCs) were found to be up-regulated in colon, colorectal and prostate cancer, but their presence in breast tissues remains uncharacterized. On the other hand, regucalcin (RGN) is a Ca(2+)-binding protein involved in the control of mammary gland cell proliferation, which has been identified as an androgen target gene in distinct tissues except breast. This study aimed to confirm the expression and activity of LTCCs in human breast cancer cells and investigate the effect of androgens in regulating the expression of α1C subunit (Cav1.2) of LTCCs and Ca(2+)-binding protein RGN. PCR, Western blot, immunofluorescence and electrophysiological experiments demonstrated the expression and activity of Cav1.2 subunit in MCF-7 cells. The MCF-7 cells were treated with 1, 10 or 100 nM of 5α-dihydrotestosterone (DHT) for 24-72 h. The obtained results showed that 1 nM DHT up-regulated the expression of Cav1.2 subunit while diminishing RGN protein levels, which was underpinned by reduced cell viability. These findings first confirmed the presence of LTCCs in breast cancer cells and opened new perspectives for the development of therapeutic approaches targeting Ca(2+) signaling.

Ovariectomy increases L-type Ca(2+) channel activity in porcine coronary smooth muscle

OBJECTIVE

Sex hormone status has been demonstrated to play a role in the regulation of ion channel activity. We previously demonstrated increased L-type Ca channel current (ICa) in the coronary smooth muscle cells (SMCs) of male swine compared with female swine. In male swine, endogenous testosterone increases ICa in SMCs by enhanced expression of the pore-forming α1 subunit Cav1.2. Conversely, the role of sex hormones in female swine has not previously been investigated. Therefore, the purpose of the current study was to determine the effect of ovariectomy (OVX) on L-type Ca channel activity and expression in female Yucatan miniature swine.

METHODS

Sexually mature female swine were obtained from a breeder and either left intact (intact female [IF]; n = 5) or ovariectomized (n = 6).

RESULTS

Sensitivity to depolarization-induced contractions was increased by OVX. Accordingly, mean (SEM) ICa was enhanced in the OVX group (-9.5 [0.6] pA/pF) compared with the IF group (-4.5 [0.3] pA/pF), although L-type Ca channel α1 subunit (Cav1.2; α1c) messenger RNA (mRNA) and protein expressions were unchanged.Among the L-type Ca channel β subunits, β1 (188 [31]) and β2a (561 [79]) had higher mRNA expression levels (target/18S) than β3 (9 [1]) and β4 (2 [0.1]). Although β2a, β3, and β4 mRNA and protein expressions were not different between groups, protein expression of the β1 subunit (Cavβ1) was decreased in the OVX group compared with the IF group.

CONCLUSIONS

Endogenous female hormones inhibit L-type Ca channel activity in coronary SMCs potentially via the up-regulation of Cavβ1 subunit expression.

Upregulation of intermediate-conductance Ca2+-activated K+ channels (KCNN4) in porcine coronary smooth muscle requires NADPH oxidase 5 (NOX5)

Aims

NADPH oxidase (NOX) is the primary source of reactive oxygen species (ROS) in vascular smooth muscle cells (SMC) and is proposed to play a key role in redox signaling involved in the pathogenesis of cardiovascular disease. Growth factors and cytokines stimulate coronary SMC (CSMC) phenotypic modulation, proliferation, and migration during atherosclerotic plaque development and restenosis. We previously demonstrated that increased expression and activity of intermediate-conductance Ca²⁺-activated K⁺ channels (KCNN4) is necessary for CSMC phenotypic modulation and progression of stenotic lesions. Therefore, the purpose of this study was to determine whether NOX is required for KCNN4 upregulation induced by mitogenic growth factors.

Methods and Results

Dihydroethidium micro-fluorography in porcine CSMCs demonstrated that basic fibroblast growth factor (bFGF) increased superoxide production, which was blocked by the NOX inhibitor apocynin (Apo). Apo also blocked bFGF-induced increases in KCNN4 mRNA levels in both right coronary artery sections and CSMCs. Similarly, immunohistochemistry and whole cell voltage clamp showed bFGF-induced increases in CSMC KCNN4 protein expression and channel activity were abolished by Apo. Treatment with Apo also inhibited bFGF-induced increases in activator protein-1 promoter activity, as measured by luciferase activity assay. qRT-PCR demonstrated porcine coronary smooth muscle expression of NOX1, NOX2, NOX4, and NOX5 isoforms. Knockdown of NOX5 alone prevented both bFGF-induced upregulation of KCNN4 mRNA and CSMC migration.

Conclusions

Our findings provide novel evidence that NOX5-derived ROS increase functional expression of KCNN4 through activator protein-1, providing another potential link between NOX, CSMC phenotypic modulation, and atherosclerosis.

Long- and short-term effects of androgens in human umbilical artery smooth muscle

The aim of the present study was to determine the effects of androgens in the regulation of human umbilical artery (HUA) contractility. The short-term effects of testosterone on the tone of the HUA were investigated, as were the long-term effects of dihydrotestosterone (DHT) on the expression of some proteins involved in the contractile process. Endothelium-denuded HUA were treated for 24 h with DHT (2 μmol/L) or the vehicle control (ethanol) to analyse the genomic effects of androgens. Twenty-four hour treatment of HUA with DHT increased the mRNA expression of the β(1)-subunit of the large-conductance Ca(2+)-activated (BK(Ca)) channel and decreased expression of the α-subunit of L-type calcium channels. In organ bath studies, testosterone (1-100 μmol/L) produced similar relaxant responses in DHT- and vehicle-treated HUA rings precontracted with 5-HT, histamine and KCl. However, the relaxation response obtained by the combined application of testosterone (100 μmol/L) and nifedipine (10 μmol/L) was significantly greater in DHT- compared with vehicle-treated HUA. The results indicate that the rapid vasorelaxant effects of testosterone that are dependent on both BK(Ca) and voltage-sensitive potassium (K(V)) channel activity in control arteries become dependent solely on K(V) channel activity in DHT-treated HUA. Thus, the present study reveals the importance of the investigation of both the short- and long-term effects of androgens in human arteries.

Contribution of electromechanical coupling between Kv and Ca v1.2 channels to coronary dysfunction in obesity

Previous investigations indicate that diminished functional expression of voltage-dependent K(+) (KV) channels impairs control of coronary blood flow in obesity/metabolic syndrome. The goal of this investigation was to test the hypothesis that KV channels are electromechanically coupled to CaV1.2 channels and that coronary microvascular dysfunction in obesity is related to subsequent increases in CaV1.2 channel activity. Initial studies revealed that inhibition of KV channels with 4-aminopyridine (4AP, 0.3 mM) increased intracellular [Ca(2+)], contracted isolated coronary arterioles and decreased coronary reactive hyperemia. These effects were reversed by blockade of CaV1.2 channels. Further studies in chronically instrumented Ossabaw swine showed that inhibition of CaV1.2 channels with nifedipine (10 μg/kg, iv) had no effect on coronary blood flow at rest or during exercise in lean swine. However, inhibition of CaV1.2 channels significantly increased coronary blood flow, conductance, and the balance between coronary flow and metabolism in obese swine (P < 0.05). These changes were associated with a ~50 % increase in inward CaV1.2 current and elevations in expression of the pore-forming subunit (α1c) of CaV1.2 channels in coronary smooth muscle cells from obese swine. Taken together, these findings indicate that electromechanical coupling between KV and CaV1.2 channels is involved in the regulation of coronary vasomotor tone and that increases in CaV1.2 channel activity contribute to coronary microvascular dysfunction in the setting of obesity.

Testosterone enhances cardiomyogenesis in stem cells and recruits the androgen receptor to the MEF2C and HCN4 genes

Since a previous study (Goldman-Johnson et al., 2008 [4]) has shown that androgens can stimulate increased differentiation of mouse embryonic stem (mES) cells into cardiomyocytes using a genomic pathway, the aim of our study is to elucidate the molecular mechanisms regulating testosterone-enhanced cardiomyogenesis. Testosterone upregulated cardiomyogenic transcription factors, including GATA4, MEF2C, and Nkx2.5, muscle structural proteins, and the pacemaker ion channel HCN4 in a dose-dependent manner, in mES cells and P19 embryonal carcinoma cells. Knock-down of the androgen receptor (AR) or treatment with anti-androgenic compounds inhibited cardiomyogenesis, supporting the requirement of the genomic pathway. Chromatin immunoprecipitation (ChIP) studies showed that testosterone enhanced recruitment of AR to the regulatory regions of MEF2C and HCN4 genes, which was associated with increased histone acetylation. In summary, testosterone upregulated cardiomyogenic transcription factor and HCN4 expression in stem cells. Further, testosterone induced cardiomyogenesis, at least in part, by recruiting the AR receptor to the regulatory regions of the MEF2C and HCN4 genes. These results provide a detailed molecular analysis of the function of testosterone in stem cells and may offer molecular insight into the role of steroids in the heart.

Gonadotropin and sex steroid levels in HIV-infected premenopausal women and their association with subclinical atherosclerosis in HIV-infected and -uninfected women in the women's interagency HIV study (WIHS)

BACKGROUND

HIV-infected women may experience prolonged amenorrhea, suggesting altered gonadotropin and sex hormone levels. However, the impact of these endocrine disruptions on atherosclerosis has not been evaluated in women living with, or at risk for, HIV infection. We investigated the association of sex hormone and gonadotropin concentrations with subclinical atherosclerosis in HIV-infected and -uninfected premenopausal women in the Women's Interagency HIV Study.

METHODS

Using B-mode ultrasound, the common carotid artery intima-media thickness and distensibility were measured once. Cycle-specific FSH, total estradiol (E2), and inhibin-B concentrations were measured in 584 (414 HIV infected, 170 HIV uninfected) women. Random concentrations of total T, dehydroepiandrosterone sulphate, and SHBG were measured in 1094 (771 HIV infected, 323 HIV uninfected) women. The endocrine analytes were measured at or before the ultrasound visit. Sex hormones, FSH, and SHBG concentrations were compared between HIV-infected and -uninfected women using nonparametric testing. Linear regression models were used to evaluate the association of sex hormones, FSH, and SHBG with carotid artery intima-media thickness and distensibility adjusted for confounders. Separate analyses were conducted by HIV status.

RESULTS

Compared with HIV-uninfected women, E2, T, and dehydroepiandrosterone sulphate concentrations were significantly lower and SHBG was higher in HIV-infected women. Adjusted for the confounders, T was significantly positively associated with distensibility (β-estimate = .04, P = .0005) among HIV-infected women, and the magnitude of association did not differ by CD4 cell count. E2 was significantly positively associated with distensibility among HIV-infected women with CD4 count less than 350 cells/μL.

CONCLUSIONS

HIV-infected women had reduced estrogen and androgen compared with HIV-uninfected premenopausal women. T deficiency is linked with carotid artery stiffness, regardless of immune suppression, whereas E2 deficiency is linked with carotid stiffness among immunocompromised HIV-infected premenopausal women. Further research is warranted to understand the impact of endocrine dysregulation on the accelerated cardiovascular disease risk in HIV-infected women.

Differential effects of androgens on coronary blood flow regulation and arteriolar diameter in intact and castrated swine

Background

Low endogenous testosterone levels have been shown to be a risk factor for the development of cardiovascular disease and cardiovascular benefits associated with testosterone replacement therapy are being advocated; however, the effects of endogenous testosterone levels on acute coronary vasomotor responses to androgen administration are not clear. The objective of this study was to compare the effects of acute androgen administration on in vivo coronary conductance and in vitro coronary microvascular diameter in intact and castrated male swine.

Methods

Pigs received intracoronary infusions of physiologic levels (1–100 nM) of testosterone, the metabolite 5α-dihydrotestosterone, and the epimer epitestosterone while left anterior descending coronary blood flow and mean arterial pressure were continuously monitored. Following sacrifice, coronary arterioles were isolated, cannulated, and exposed to physiologic concentrations (1–100 nM) of testosterone, 5α-dihydrotestosterone, and epitestosterone. To evaluate effects of the androgen receptor on acute androgen dilation responses, real-time PCR and immunohistochemistry for androgen receptor were performed on conduit and resistance coronary vessels.

Results

In vivo, testosterone and 5α-dihydrotestosterone produced greater increases in coronary conductance in the intact compared to the castrated males. In vitro, percent maximal dilation of microvessels was similar between intact and castrated males for testosterone and 5α-dihydrotestosterone. In both studies epitestosterone produced significant increases in conductance and microvessel diameter from baseline in the intact males. Androgen receptor mRNA expression and immunohistochemical staining were similar in intact and castrated males.

Conclusions

Acute coronary vascular responses to exogenous androgen administration are increased by endogenous testosterone, an effect unrelated to changes in androgen receptor expression.

Testosterone-induced relaxation of coronary arteries: activation of BKCa channels via the cGMP-dependent protein kinase

Androgens are reported to have both beneficial and detrimental effects on human cardiovascular health. The aim of this study was to characterize nongenomic signaling mechanisms in coronary artery smooth muscle (CASM) and define the ionic basis of testosterone (TES) action. TES-induced relaxation of endothelium-denuded porcine coronary arteries was nearly abolished by 20 nM iberiotoxin, a highly specific inhibitor of large-conductance, calcium-activated potassium (BK(Ca)) channels. Molecular patch-clamp studies confirmed that nanomolar concentrations of TES stimulated BK(Ca) channel activity by ∼100-fold and that inhibition of nitric oxide synthase (NOS) activity by N(G)-monomethyl-L-arginine nearly abolished this effect. Inhibition of nitric oxide (NO) synthesis or guanylyl cyclase activity also attenuated TES-induced coronary artery relaxation but did not alter relaxation due to 8-bromo-cGMP. Furthermore, we detected TES-stimulated NO production in porcine coronary arteries and in human CASM cells via stimulation of the type 1 neuronal NOS isoform. Inhibition of the cGMP-dependent protein kinase (PKG) attenuated TES-stimulated BK(Ca) channel activity, and direct assay determined that TES increased activity of PKG in a concentration-dependent fashion. Last, the stimulatory effect of TES on BK(Ca) channel activity was mimicked by addition of purified PKG to the cytoplasmic surface of a cell-free membrane patch from CASM myocytes (∼100-fold increase). These findings indicate that TES-induced relaxation of endothelium-denuded coronary arteries is mediated, at least in part, by enhanced NO production, leading to cGMP synthesis and PKG activation, which, in turn, opens BK(Ca) channels. These findings provide a molecular mechanism that could help explain why androgens have been reported to relax coronary arteries and relieve angina pectoris.

L-type calcium channel auto-regulation of transcription

L-type calcium channels (LTCC) impact the function of nearly all excitable cells. The classical LTCC function is to mediate trans-sarcolemmal Ca(2+) flux. This review focuses on the contribution of a mobile segment of the LTCC that regulates ion channel function, and also serves as a regulator of transcription in the nucleus. Specifically we highlight recent work demonstrating an auto-feedback regulatory pathway whereby the LTCC transcription factor regulates the LTCC. Also discussed is acute and long-term regulation of function by the LTCC-transcription regulator.

Progesterone treatment inhibits and dihydrotestosterone (DHT) treatment potentiates voltage-gated calcium currents in gonadotropin-releasing hormone (GnRH) neurons

GnRH neurons are central regulators of fertility, and their activity is modulated by steroid feedback. In normal females, GnRH secretion is regulated by estradiol and progesterone (P). Excess androgens present in hyperandrogenemic fertility disorders may disrupt communication of negative feedback signals from P and/or independently stimulate GnRH release. Voltage-gated calcium channels (VGCCs) are important in regulating excitability and hormone release. Estradiol alters VGCCs in a time-of-day-dependent manner. To further elucidate ovarian steroid modulation of GnRH neuron VGCCs, we studied the effects of dihydrotestosterone (DHT) and P. Adult mice were ovariectomized (OVX) or OVX and treated with implants containing DHT (OVXD), estradiol (OVXE), estradiol and DHT (OVXED), estradiol and P (OVXEP), or estradiol, DHT, and P (OVXEDP). Macroscopic calcium current (I(Ca)) was recorded in the morning or afternoon 8-12 d after surgery using whole-cell voltage-clamp. I(Ca) was increased in afternoon vs. morning in GnRH neurons from OVXE mice but this increase was abolished in cells from OVXEP mice. I(Ca) in cells from OVXD mice was increased regardless of time of day; there was no additional effect in OVXED mice. P reduced N-type and DHT potentiated N- and R-type VGCCs; P blocked the DHT potentiation of N-type-mediated current. These data suggest P and DHT have opposing actions on VGCCs in GnRH neurons, but in the presence of both steroids, P dominates. VGCCs are targets of ovarian steroid feedback modulation of GnRH neuron activity and, more specifically, a potential mechanism whereby androgens could activate GnRH neuronal function.

Regulation of ryanodine receptor-mediated Ca(2+) release in vas deferens smooth muscle cells

Ca(2+) release from intracellular store sites via the ryanodine receptor (RyR) and hormonal regulation by flutamide, an androgen-receptor (AR) antagonist, on it were examined in vas deferens (VD) smooth muscle cells (SMCs). VD and VDSMCs were obtained from two groups of male rats that were treated p.o. with 100 mg/kg flutamide (Flu) or vehicle (Vehicle). Both spontaneous and caffeine-induced Ca(2+) releases were markedly smaller in single VDSMCs from Flu than in those from Vehicle. Interestingly, [Ca(2+)](i) rise by 100 muM norepinephrine in VDSMCs from Flu was larger than that in those from Vehicle. The contractions induced by direct electrical stimulation in tissue preparations from Flu showed lower susceptibility to 30 muM ryanodine than those from Vehicle. Real-time PCR analyses revealed that the transcripts of ryanodine receptor (RyR) type 2 and type 3 (RyR2 and RyR3) were expressed in VD and markedly reduced in Flu. The protein expression of total RyR was significantly reduced by flutamide treatment, but that of inositol 1,4,5-trisphosphate receptor (IP3R) was not affected. It can be strongly suggested that long term block of AR by flutamide reduced the expression of RyR and its contribution to the contraction, but not those of IP3R in VDSMCs.

Endogenous testosterone attenuates neointima formation after moderate coronary balloon injury in male swine

AIMS

Previous studies from our laboratory have demonstrated that testosterone increases coronary smooth muscle protein kinase C delta (PKC delta) both in vivo and in vitro and inhibits coronary smooth muscle proliferation by inducing G(0)/G(1) cell cycle arrest in a PKC delta-dependent manner. The purpose of the present study was to determine whether endogenous testosterone limits coronary neointima (NI) formation in a porcine model of post-angioplasty restenosis.

METHODS AND RESULTS

Sexually mature, male Yucatan miniature swine were either left intact (IM), castrated (CM), or castrated with testosterone replacement (CMT; Androgel, 10 mg/day). Angioplasty was performed in both the left anterior descending and left circumflex coronary arteries with balloon catheter overinflation to induce either moderate (1.25-1.3 x diameter; 3 x 30 s) or severe (1.4x diameter; 3 x 30 s) injury, and animals were allowed to recover for either 10 or 28 days. Injured coronary sections were dissected, fixed, stained (Verheoff-Van Gieson, Ki67, PKC delta, p27), and analysed. Vessels without internal elastic laminal rupture were excluded. Following moderate injury, intimal area, intima-to-media ratio (I/M), and I/M normalized to rupture index (RI) were increased in CM compared with IM and CMT. RI, medial area, and intimal/medial thickness (IMT) were not different between groups. NI formation was inversely related to serum testosterone concentration. Conversely, following severe injury, there were no significant differences between the groups. Testosterone inhibited proliferation and stimulated PKC delta and p27(kip1) expression during NI formation (10 days post-injury).

CONCLUSION

These findings demonstrate that endogenous testosterone limits coronary NI formation in male swine and provides support for a protective role for testosterone in coronary vasculoproliferative diseases, such as restenosis and atherosclerosis.

Castration modifies aortic vasoreactivity and serum fatty acids in a sucrose-fed rat model of metabolic syndrome

Levels of testosterone and estradiol influence the incidence of cardiovascular diseases: generally, estrogens in females are protective before menopause; coronaropathies, hypertension, and dyslipidemias in normal men are more frequent at comparable ages. We investigated the modulation by castration of in vitro vasoreactivity, serum lipid content, and systolic blood pressure (SBP) in rats with sucrose-induced metabolic syndrome. The main characteristics of the rat model are: hypertriglyceridemia, moderately high blood pressure, intra-abdominal accumulation of adipose tissue, hyperinsulinemia, nephropathy, increased oxidative stress, and altered vasoreactivity. Male weanling rats received 30% sucrose solution for 16 weeks (metabolic syndrome; MS), controls (C) had plain water; both had commercial rodent chow. They were subdivided into five groups with two subgroups each: Group 1, intact C and MS rats, Groups 2-5, C and MS rats castrated for periods of 16, 12, 8, and 4 weeks. At the end of the study period, systolic blood pressure was measured, and blood and aortas were obtained for fatty acid determination and vasoreactivity assays, respectively. After 16 weeks' sucrose treatment MS aortas showed hypercontractility and decreased vasodilation. Palmitic and palmitoleic acids were increased in MS versus C. Arachidonic acid levels in MS were lower than in intact or castrated C. Long-term castration of 16 weeks normalized the levels of palmitic and oleic acids. With the shorter periods of castration, contractility increased and relaxation decreased in C and MS, but it was more significant in C. Regarding fatty acid composition, long-term castration increased polyunsaturated (arachidonic and eicosapentaenoic) fatty acids. The shorter periods did not modify the fatty acid profile in either C or MS. Metabolic syndrome altered SBP, aortic reactivity, and levels of fatty acids; castration of long duration normalized them in some cases.

Gabapentin neuroprotection and seizure suppression in immature mouse brain ischemia

Stroke is a major cause of neurologic morbidity in neonates and children. Because neonatal and pediatric stroke frequently present with seizures, the question of which anticonvulsant best blocks acute ischemic seizures and reduces injury is clinically relevant. The purpose of this study was to determine the extent to which gabapentin is neuroprotective and suppresses acute seizures in this model of ischemic injury in the immature brain. Postnatal day 12 CD1 mice underwent right common carotid artery ligation and immediately after ligation received a 0, 50, 100, 150, or 200 mg/kg dose of gabapentin intraperitoneally. Acute seizure activity was behaviorally scored and hemispheric brain atrophy measured. In vehicle-treated mice, severity of acute seizures correlated with hemispheric brain atrophy 4 wks later. Gabapentin significantly decreased acute seizures at 200 mg/kg and reduced brain atrophy at doses of 150 and 200 mg/kg but not at lower doses. These results suggest that gabapentin effectively reduces acute seizures and injury after ischemia in the immature brain. When analyzed by animal sex, the data suggest that gabapentin may more effectively reduce acute seizures and injury in male pups vs. female pups.

Local delivery of the KCa3.1 blocker, TRAM-34, prevents acute angioplasty-induced coronary smooth muscle phenotypic modulation and limits stenosis

OBJECTIVE

We previously demonstrated that upregulation of intermediate-conductance Ca(2+)-activated K(+) channels (K(Ca)3.1) is necessary for mitogen-induced phenotypic modulation in isolated porcine coronary smooth muscle cells (SMCs). The objective of the present study was to determine the role of K(Ca)3.1 in the regulation of coronary SMC phenotypic modulation in vivo using a swine model of postangioplasty restenosis.

METHODS AND RESULTS

Balloon angioplasty was performed on coronary arteries of swine using either noncoated or balloons coated with the specific K(Ca)3.1 blocker TRAM-34. Expression of K(Ca)3.1, c-jun, c-fos, repressor element-1 silencing transcription factor (REST), smooth muscle myosin heavy chain (SMMHC), and myocardin was measured using qRT-PCR in isolated medial cells 2 hours and 2 days postangioplasty. K(Ca)3.1, c-jun, and c-fos mRNA levels were increased 2 hours postangioplasty, whereas REST expression decreased. SMMHC expression was unchanged at 2 hours, but decreased 2 days postangioplasty. Use of TRAM-34 coated balloons prevented K(Ca)3.1 upregulation and REST downregulation at 2 hours, SMMHC and myocardin downregulation at 2 days, and attenuated subsequent restenosis 14 and 28 days postangioplasty. Immunohistochemical analysis demonstrated corresponding changes at the protein level.

CONCLUSIONS

Blockade of K(Ca)3.1 by delivery of TRAM-34 via balloon catheter prevented smooth muscle phenotypic modulation and limited subsequent restenosis.

Enhanced muscle fatigue occurs in male but not female ASIC3-/- mice

Muscle fatigue is associated with a number of clinical diseases, including chronic pain conditions. Decreases in extracellular pH activates acid-sensing ion channel 3 (ASIC3), depolarizes muscle, protects against fatigue, and produces pain. We examined whether ASIC3-/- mice were more fatigable than ASIC3+/+ mice in a task-dependent manner. We developed two exercise protocols to measure exercise-induced muscle fatigue: (fatigue task 1, three 1-h runs; fatigue task 2, three 30-min runs). In fatigue task 1, male ASIC3+/+ mice muscle showed less fatigue than male ASIC3-/- mice and female ASIC3+/+ mice. No differences in fatigue were observed in fatigue task 2. We then tested whether the development of muscle fatigue was dependent on sex and modulated by testosterone. Female ASIC3+/+ mice that were ovariectomized and administered testosterone developed less muscle fatigue than female ASIC3+/+ mice and behaved similarly to male ASIC3+/+ mice. However, testosterone was unable to rescue the muscle fatigue responses in ovariectomized ASIC3-/- mice. Plasma levels of testosterone from male ASIC3-/- mice were significantly lower than in male ASIC3+/+ mice and were similar to female ASIC3+/+ mice. Muscle fiber types, measured by counting ATPase-stained whole muscle sections, were similar in calf muscles from male and female ASIC3+/+ mice. These data suggest that both ASIC3 and testosterone are necessary to protect against muscle fatigue in a task-dependent manner. Also, differences in expression of ASIC3 and the development of exercise-induced fatigue could explain the female predominance in clinical syndromes of pain that include muscle fatigue.

PKCδ mediates anti-proliferative, pro-apoptic effects of testosterone on coronary smooth muscle

Sex hormone status has emerged as an important modulator of coronary physiology and cardiovascular disease risk in both males and females. Our previous studies have demonstrated that testosterone increases protein kinase C (PKC) δ expression and activity in coronary smooth muscle (CSMC). Because PKCδ has been implicated in regulation of proliferation and apoptosis in other cell types, we sought to determine if testosterone modulates CSMC proliferation and/or apoptosis through PKCδ. Porcine CSMC cultures (passages 2–6) from castrated males were treated with testosterone for 24 h. Testosterone (20 and 100 nM) decreased [3H]thymidine incorporation in proliferating CSMC to 59 ± 5.3 and 33.1 ± 4.5% of control. Flow cytometric analysis demonstrated that testosterone induced G1arrest in CSMC with a concomitant reduction in the S phase cells. Testosterone reduced protein levels of cyclins D1and E and phosphorylation of retinoblastoma protein while elevating levels of p21cip1and p27kip1. There were no significant differences in the levels of cyclins D3, CDK2, CDK4, or CDK6. Testosterone significantly reduced kinase activity of CDK2 and -6, but not CDK4, -7, or -1. PKCδ small interfering RNA (siRNA) prevented testosterone-mediated G1arrest, p21cip1upregulation, and cyclin D1and E downregulation. Furthermore, testosterone increased CSMC apoptosis in a dose-dependent manner, which was blocked by either PKCδ siRNA or caspase 3 inhibition. These findings demonstrate that the anti-proliferative, pro-apoptotic effects of testosterone on CSMCs are substantially mediated by PKCδ.

Physiological testosterone stimulates tissue plasminogen activator and tissue factor pathway inhibitor and inhibits plasminogen activator inhibitor type 1 release in endothelial cells

There is a striking gender difference in atherosclerotic vascular disease. For decades, testosterone was considered detrimental to the cardiovascular system. Recent studies, however, have presented some alternative results. The aim of this study was to evaluate the effect of testosterone, using physiological and supraphysiological concentrations, on antigen and mRNA levels of tissue plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1), and tissue factor pathway inhibitor (TFPI) released by human umbilical vein endothelial cells and to investigate the cellular mechanism. Cells within 2-3 passages were cultured in 25 cm(2) flasks or plated onto 96-well plates with a density of about 1 x 10(5) cells/mL as recommended. The cells were incubated in the presence or absence of testosterone (3, 30, 3 x 10(3), 3 x 10(4) nmol/L) for 48 h. Levels of tPA, PAI-1, and TFPI antigen were assayed with ELISA kits. Reverse transcriptase PCR was carried out to detect tPA, PAI-1, and TFPI mRNA levels. Cells were incubated in androgen-receptor antagonist (flutamide 10 micromol/L) or aromatase inhibitor (aminoglutethimide 50 micromol/L) for 3 h, and then the experiments were repeated. Testosterone at a physiologic concentration (30 nmol/L) increased the antigen levels of tPA and TFPI significantly (P < 0.05). However, tPA and TFPI levels were markedly reduced (P < 0.05) at a larger dose (3 x 10(4) nmol/L). On the other hand, PAI-1 antigen levels decreased significantly at the testosterone concentrations ranging from 3 to 3 x 10(4) nmol/L (P < 0.05). The change in the levels of tPA and TFPI were reflected in the corresponding change in mRNA levels. Flutamide attenuated the effect of testosterone at physiological concentration (30 nmol/L). The results demonstrated that testosterone at physiological concentrations may have a beneficial influence on the haemostatic system through enhancement of anticoagulant activity, resulting from stimulation of TFPI and tPA expression and inhibition of PAI-1 secretion by the endothelium.

Impact of testosterone on cardiac L-type calcium channels and Ca2+ sparks: acute actions antagonize chronic effects

While androgens generally have been associated with an increased cardiovascular risk, recent studies indicate potential beneficial acute effects of testosterone. However, detailed evaluation of chronic and acute actions of testosterone on the function of cardiac I(Ca,L) and intracellular Ca2+ handling is limited. To clarify this situation we performed whole-cell and single-channel analysis of I(Ca,L), recordings of Ca2+ sparks, measurements of contractility and quantitative real-time RT-PCR in rat cardiomyocytes following testosterone pretreatment and acute testosterone application. Pretreatment with testosterone 100 nM for 24-30 h increased whole-cell I(Ca,L) from 3.8+/-0.8 pA/pF (n=10) to 10.1+/-0.31 pA/pF (n=9) at +10 mV (p<0.001). Increase of I(Ca,L) density was caused by both, increased expression levels of the alpha 1C subunit of L-type calcium channel and a pronounced increment of the single-channel activity (availability 81.8+/-3.15% versus 37.1+/-7.01%; open probability 12.8+/-3.09% versus 1.0+/-0.62%, p<0.01). Moreover, testosterone pretreatment significantly increased the frequency of Ca2+ sparks and improved myocytes contractility without altering SR Ca2+ load. All chronic effects could be inhibited by flutamide. In contrast acute testosterone administration significantly reduced I(Ca,L) density. Indeed, on the single-channel level acute testosterone application completely reversed the chronic testosterone-mediated effects, and antagonized the chronic testosterone effects on Ca2+ spark frequency, which was unaffected by flutamide. Thus, testosterone pretreatment activates I(Ca,L) via nuclear receptor-mediated pathways, while testosterone acutely blocks I(Ca,L) in a direct manner. Thus, testosterone chronically affects the basal level of intracellular Ca2+ handling, which in addition rapidly may be modulated by acute changes of hormone levels.

Long-term and immediate effect of testosterone on single T-type calcium channel in neonatal rat cardiomyocytes

In the cardiovascular system, T-type calcium channels play an important role for the intracellular calcium homeostasis and spontaneous pacemaker activity and are involved in the progression of structural heart diseases. Androgens influence the cardiovascular physiology and pathophysiology. However, their effect on native T-type calcium currents (I(Ca,T)) remains unclear. To test the chronic effect of testosterone on the cardiac I(Ca,T), cultured neonatal rat ventricular cardiomyocytes were treated with testosterone (1 nM-10 microM) for 24-30 h. Current measurements were performed after testosterone washout to exclude any acute testosterone effects. Testosterone (100 nm) pretreatment significantly increased whole-cell I(Ca,T) density from 1.26 +/- 0.48 pA/pF (n = 8) to 5.06 +/- 1.75 pA/pF (n = 7; P < 0.05) and accelerated beating rate. This was attributed to both increased expression levels of the pore-forming subunits Ca(v)3.1 and Ca(v)3.2 and increased T-type single-channel activity. On single-channel level, the increase of the ensemble average current by testosterone vs. time-matched controls was due to an increased availability (58.1 +/- 4.2 vs. 21.5 +/- 4.0%, P < 0.01) and open probability (2.78 +/- 0.29 vs. 0.85 +/- 0.23%, P < 0.01). Cotreatment with the selective testosterone receptor antagonist flutamide (10 mum) prevented these chronic testosterone-induced effects. Conversely, acute application of testosterone (10 microM) decreased T-type single-channel activity in testosterone pretreated cells by reducing the open probability (0.78 +/- 0.13 vs. 2.91 +/- 0.38%, P < 0.01), availability (23.6 +/- 3.3 vs. 57.6 +/- 4.5%, P < 0.01), and peak current (-20 +/- 4 vs. -58 +/- 4 fA, P < 0.01). Flutamide (10 microM) did not abolish the testosterone-induced acute block of T-type calcium channels. Our results indicate that long-term testosterone treatment increases, whereas acute testosterone decreases neonatal rat T-type calcium currents. These effects seem to be mediated by a genomic chronic stimulation and a nongenomic acute inhibitory action.

Testosterone replacement therapy in male hypogonadism is not associated with increase of endothelin-1 levels

Differences in endothelin-1 (ET-1) blood plasma levels were established between healthy men and women. Little is known about vascular effects of testosterone and the interactions between sex hormones and endothelin. In order to study the relationship between ET-1 and testosterone in more detail, we have investigated 33 male patients with various forms of hypogonadism (13 with hypergonadotropic hypogonadism and 20 with hypogonadotropic hypogonadism). Fourteen age-matched healthy males served as controls. The basal ET-1 levels in patients with hypogonadism (0.96 +/- 0.12 fmol/mL) (mean +/- SEM) were significantly higher in comparison with the controls (0.44 +/- 0.04 fmol/mL), p < 0.01. Fifteen individuals of these patients were studied during the therapy with testosterone depot 250 mg i.m. The ET-1 levels decreased in this group from 0.99 +/- 0.22 to 0.78 +/- 0.14 fmol/mL at the third and to 0.76 +/- 0.25 fmol/mL at the sixth month of the medication, respectively. The differences were not significant compared with the initial levels, but the concentrations at the sixth month of the treatment were not statistically different in comparison with the ET-1 levels of the controls. There was no significant difference in lipid data between patients before and during testosterone medication, except for the high-density lipoprotein cholesterol, which decreased at the third month of the treatment. Our results show that plasma ET-1 levels in males with hypogonadism are elevated with a tendency to decrease after testosterone administration. The optimum testosterone is not associated with enhanced cardiovascular risk as far as ET-1 plasma levels and lipids are concerned.

Upregulation of intermediate-conductance Ca2+-activated K+ channel (IKCa1) mediates phenotypic modulation of coronary smooth muscle

A hallmark of smooth muscle cell (SMC) phenotypic modulation in atherosclerosis and restenosis is suppression of SMC differentiation marker genes, proliferation, and migration. Blockade of intermediate-conductance Ca(2+)-activated K(+) channels (IKCa1) has been shown to inhibit restenosis after carotid balloon injury in the rat; however, whether IKCa1 plays a role in SMC phenotypic modulation is unknown. Our objective was to determine the role of IKCa1 channels in regulating coronary SMC phenotypic modulation and migration. In cultured porcine coronary SMCs, platelet-derived growth factor-BB (PDGF-BB) increased TRAM-34 (a specific IKCa1 inhibitor)-sensitive K(+) current 20-fold; increased IKCa1 promoter histone acetylation and c-jun binding; increased IKCa1 mRNA approximately 4-fold; and potently decreased expression of the smooth muscle differentiation marker genes smooth muscle myosin heavy chain (SMMHC), smooth muscle alpha-actin (SMalphaA), and smoothelin-B, as well as myocardin. Importantly, TRAM-34 completely blocked PDGF-BB-induced suppression of SMMHC, SMalphaA, smoothelin-B, and myocardin and inhibited PDGF-BB-stimulated migration by approximately 50%. Similar to TRAM-34, knockdown of endogenous IKCa1 with siRNA also prevented the PDGF-BB-induced increase in IKCa1 and decrease in SMMHC mRNA. In coronary arteries from high fat/high cholesterol-fed swine demonstrating signs of early atherosclerosis, IKCa1 expression was 22-fold higher and SMMHC, smoothelin-B, and myocardin expression significantly reduced in proliferating vs. nonproliferating medial cells. Our findings demonstrate that functional upregulation of IKCa1 is required for PDGF-BB-induced coronary SMC phenotypic modulation and migration and support a similar role for IKCa1 in coronary SMC during early coronary atherosclerosis.

Some thoughts on the vasculopathy of women with ischemic heart disease

Considerable experimental and clinical data indicate that sex has an important influence on cardiovascular physiology and pathology. This report integrates selected literature with new data from the Women's Ischemia Syndrome Evaluation (WISE) on vascular findings in women with ischemic heart disease (IHD) and how these findings differ from those in men. A number of common vascular disease-related conditions are either unique to (e.g., hypertensive disorders of pregnancy, gestational diabetes, peripartum dissection, polycystic ovarian syndrome, etc.) or more frequent (e.g., migraine, coronary spasm, lupus, vasculitis, Raynaud's phenomenon, etc.) in women than men. Post-menopausal women more frequently have many traditional vascular disease risk conditions (e.g., hypertension, diabetes, obesity, inactivity, and so on), and these conditions cluster more frequently in them than men. Considerable evidence supports the notion that, with these requisite conditions, women develop a more severe or somewhat different form of vascular disease than men. Structurally, women's coronary vessels are smaller in size and appear to contain more diffuse atherosclerosis, their aortas are stiffer (fibrosis, remodeling, and so on), and their microvessels appear to be more frequently dysfunctional compared with men. Functionally, women's vessels frequently show impaired vasodilator responses. Limitations of existing data and higher risks in women with acute myocardial infarction, need for revascularization, or heart failure create uncertainty about management. A better understanding of these findings should provide direction for new algorithms to improve management of the vasculopathy underlying IHD in women.

Vascular calcium channels and high blood pressure: pathophysiology and therapeutic implications

Long-lasting Ca(2+) (Ca(L)) channels of the Ca(v)1.2 gene family are heteromultimeric structures that are minimally composed of a pore-forming alpha(1C) subunit and regulatory beta and alpha(2)delta subunits in vascular smooth muscle cells. The Ca(L) channels are the primary pathways for voltage-gated Ca(2+) influx that trigger excitation-contraction coupling in small resistance vessels. Notably, vascular smooth muscle cells of hypertensive rats show an increased expression of Ca(L) channel alpha(1C) subunits, which is associated with elevated Ca(2+) influx and the development of abnormal arterial tone. Indeed, blood pressure per se appears to promote Ca(L) channel expression in small arteries, and even short-term rises in pressure may alter channel expression. Membrane depolarization has been shown to be one stimulus associated with elevated blood pressure that promotes Ca(L) channel expression at the plasma membrane. Future studies to define the molecular processes that regulate Ca(L) channel expression in vascular smooth muscle cells will provide a rational basis for designing antihypertensive therapies to normalize Ca(L) channel expression and the development of anomalous vascular tone in hypertensive pathologies.

Isoform-specific modulation of coronary artery PKC by glucocorticoids

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-alpha, -betaII, -epsilon, -delta, and -zeta specific antibodies. Dexamethasone caused a approximately 4-fold increase in PKC-alpha, a approximately 2.5-fold increase in PKC-betaII, and a 2-fold increase in PKC-epsilon (p<0.05). In contrast, dexamethasone had no effect on PKC-delta or PKC- zeta levels. Dexamethasone also caused an increase in the activity of PKC-alpha (285%), -betaII (170%), and -epsilon (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-alpha, -betaII and -epsilon, no such effect was observed for PKC-delta or PKC-zeta. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.