Extracellular calcium regulates expression of the gene for atrial natriuretic factor

Attenuated β-adrenergic response in calcium/calmodulin-dependent protein kinase IV-knockout mice

In the present study, we examined the importance of Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) in the regulation of cardiac function using genetically modified CaMKIV-null mice. RT-PCR analysis revealed decreased expression of voltage-dependent calcium channels in the cardiac myocytes of CaMKIV-null mice compared with wild-type mice. CaMKIV-null mice showed shortened QT time on electrocardiograms. Pharmacological analysis revealed decreased responsiveness to the β-adrenergic blocker propranolol in CaMKIV-null mice, whereas the plasma norepinephrine level was not affected. CaMKIV-null mice showed decreased baroreflex on electrocardiograms. Heart rate variability analysis showed unstable R-R intervals, a decreased low frequency power/high frequency power (LF/HF) ratio, and increased standard deviation of the normal to normal R-R intervals (SDNN) in CaMKIV-null mice, suggesting decreased responsiveness to β-adrenergic stimulation in CaMKIV-null mice. Atrial contraction analysis and cardiac action potential recording showed a decreased response to the β-adrenoceptor agonist isoproterenol in CaMKIV-null mice. Furthermore, fluorescence imaging in a CRE-hrGFP assay revealed a decreased response to isoproterenol in CaMKIV-null cardiac myocytes. Taken together, our data strongly suggest a significant effect of CaMKIV gene ablation on cardiac β-adrenergic signal transduction.

Calcium Carbonate Attenuates Withdrawal and Reduces Craving: A Randomized Controlled Trial in Alcohol-Dependent Patients

INTRODUCTION

Preclinical studies have shown that calcium seems to be the active component of the anti-craving drug acamprosate (Ca2+ bis-acetyl-homotaurinate). Clinical effects in humans have also indicated an association between increased calcium plasma concentration due to acamprosate treatment and better outcome relating to time to relapse and cumulative abstinence. In contrast, low calcium concentration in alcohol-dependent patients was related with craving for alcohol. The main goal of the trial was to investigate whether an oral calcium administration is able to affect craving, withdrawal, and relapse risk in alcohol-dependent patients.

METHODS

We conducted a single-blind, randomized, monocentric, controlled clinical two-arm trial in alcohol-dependent patients (Clinical Trials Registration: DRKS00011293). A total of 55 alcohol-dependent subjects received calcium carbonate (800 mg + 5 μg vitamin D) versus sodium bicarbonate (1,000 mg) daily during the 14 days of inpatient alcohol-withdrawal treatment.

RESULTS

Based on an intention-to-treat protocol, withdrawal intensity (assessed with CIWA-Ar) in the calcium carbonate group attenuated faster than in the sodium bicarbonate subgroup. Alcohol craving (assessed with OCDS) in the calcium carbonate subgroup was also significantly reduced versus the sodium bicarbonate subgroup.

CONCLUSION

Our data support earlier findings and show that treatment with calcium carbonate during alcohol withdrawal reduces symptoms of alcohol withdrawal as well as alcohol craving in a controlled clinical pilot study. Mode of actions will need to be determined to allow the further development of pharmacological interventions beyond Ca2+ bis-acetyl-homotaurinate.

Calcium handling proteins: structure, function, and modulation by exercise

Heart failure is a serious public health issue with a growing prevalence, and it is related with the aging of the population. Hypertension is identified as the main precursor of left ventricular hypertrophy and therefore can lead to diastolic dysfunction and heart failure. Scientific studies have confirmed the beneficial effects of the physical exercise by reducing the blood pressure and improving the functional status of the heart in hypertension. Several proteins are involved in the mobilization of calcium during the coupling excitation-contraction process in the heart among those are sarcoplasmic reticulum Ca(2+)-ATPase, phospholamban, calsequestrin, sodium-calcium exchanger, L-type calcium's channel, and ryanodine receptors. Our goal is to address the beneficial effects of exercise on the calcium handling proteins in a heart with hypertension.

Treatment of Obese Female and MaleSHHF/Mcc-facpRats with Antihypertensive Drugs, Nifedipine and Enalapril: Effects on Body Weight, Fat Distribution, Insulin Resistance and Systolic Pressure

Little is known about the effects of common antihypertensive drugs in obese, insulin-resistant females. Nine-month-old obese female SHHF/Mcc-fa(cp) rats that received either nifedipine, a calcium channel antagonist, or enalapril, an angiotensin-converting-enzyme inhibitor, for three months were compared with untreated SHHF/Mcc-fa(cp) rats (controls). After one month, nifedipine significantly decreased body weight in obese females compared to either enalapril or controls. After three months of treatment, total, abdominal, and subcutaneous fat masses were decreased in obese females given nifedipine compared to either enalapril or controls. Enalapril treatment was associated with a redistribution of fat mass from abdominal to subcutaneous depots. Nifedipine reduced plasma triglyceride and fasting glucose levels and improved insulin response to an oral glucose load in obese females, whereas enalapril did not appear to affect glycemic control. Systolic pressure was not significantly decreased until after two months of treatment with nifedipine or three months of treatment with enalapril in obese females and may have coincided with improvement in insulin-resistance. Similarly, plasma atrial natriuretic peptide concentrations were significantly lower in obese females given nifedipine. To determine how obese males responded to a calcium channel antagonist, six-month-old obese male SHHF/Mcc-fa(cp) rats were treated for three months with either nifedipine or placebo (controls). Nifedipine-treated obese males showed a mild but significant decrease in weight gain that was due to a decrease in fat deposition in both subcutaneous and abdominal depots and systolic blood pressure was significantly reduced after one month of treatment. Nifedipine did not affect other plasma biochemical parameters in obese males. In conclusion, nifedipine improved systolic pressure and glycemic control in obese female SHHF/Mcc-fa(cp) rats, effects that may be associated with a marked loss in body weight and fat mass and improved lipid metabolism. Nifedipine-treated obese males exhibited only a diminished weight gain that was not associated with changes in diabetic characteristics.

Calcineurin selectively docks with the dynamin Ixb splice variant to regulate activity-dependent bulk endocytosis

Depolarization of nerve terminals stimulates rapid dephosphorylation of two isoforms of dynamin I (dynI), mediated by the calcium-dependent phosphatase calcineurin (CaN). Dephosphorylation at the major phosphorylation sites Ser-774/778 promotes a dynI-syndapin I interaction for a specific mode of synaptic vesicle endocytosis called activity-dependent bulk endocytosis (ADBE). DynI has two main splice variants at its extreme C terminus, long or short (dynIxa and dynIxb) varying only by 20 (xa) or 7 (xb) residues. Recombinant GST fusion proteins of dynIxa and dynIxb proline-rich domains (PRDs) were used to pull down interacting proteins from rat brain nerve terminals. Both bound equally to syndapin, but dynIxb PRD exclusively bound to the catalytic subunit of CaNA, which recruited CaNB. Binding of CaN was increased in the presence of calcium and was accompanied by further recruitment of calmodulin. Point mutations showed that the entire C terminus of dynIxb is a CaN docking site related to a conserved CaN docking motif (PXIXI(T/S)). This sequence is unique to dynIxb among all other dynamin variants or genes. Peptide mimetics of the dynIxb tail blocked CaN binding in vitro and selectively inhibited depolarization-evoked dynI dephosphorylation in nerve terminals but not of other dephosphins. Therefore, docking to dynIxb is required for the regulation of both dynI splice variants, yet it does not regulate the phosphorylation cycle of other dephosphins. The peptide blocked ADBE, but not clathrin-mediated endocytosis of synaptic vesicles. Our results indicate that Ca(2+) influx regulates assembly of a fully active CaN-calmodulin complex selectively on the tail of dynIxb and that the complex is recruited to sites of ADBE in nerve terminals.

Ca2+ influx through T- and L-type Ca2+ channels have different effects on myocyte contractility and induce unique cardiac phenotypes

T-type Ca(2+) channels (TTCCs) are expressed in the developing heart, are not present in the adult ventricle, and are reexpressed in cardiac diseases involving cardiac dysfunction and premature, arrhythmogenic death. The goal of this study was to determine the functional role of increased Ca(2+) influx through reexpressed TTCCs in the adult heart. A mouse line with cardiac-specific, conditional expression of the alpha1G-TTCC was used to increase Ca(2+) influx through TTCCs. alpha1G hearts had mild increases in contractility but no cardiac histopathology or premature death. This contrasts with the pathological phenotype of a previously studied mouse with increased Ca(2+) influx through the L-type Ca(2+) channel (LTCC) secondary to overexpression of its beta2a subunit. Although alpha1G and beta2a myocytes had similar increases in Ca(2+) influx, alpha1G myocytes had smaller increases in contraction magnitude, and, unlike beta2a myocytes, there were no increases in sarcoplasmic reticulum Ca(2+) loading. Ca(2+) influx through TTCCs also did not induce normal sarcoplasmic reticulum Ca(2+) release. alpha1G myocytes had changes in LTCC, SERCA2a, and phospholamban abundance, which appear to be adaptations that help maintain Ca(2+) homeostasis. Immunostaining suggested that the majority of alpha1G-TTCCs were on the surface membrane. Osmotic shock, which selectively eliminates T-tubules, induced a greater reduction in L- versus TTCC currents. These studies suggest that T- and LTCCs are in different portions of the sarcolemma (surface membrane versus T-tubules) and that Ca(2+) influx through these channels induce different effects on myocyte contractility and lead to distinct cardiac phenotypes.

Regulation of phospholamban and sarcoplasmic reticulum Ca2+-ATPase by atorvastatin: implication for cardiac hypertrophy

Abnormal intracellular Ca2+ homeostasis in the myocardium has been suggested as the cause of cardiac hypertrophy, and this process can be prevented by the HMG-CoA reductase inhibitors, statins. In the present study, the effect of atorvastatin on left ventricular hypertrophy was investigated, and then whether the underlying mechanism was related to a defect in intracellular Ca2+ homeostasis explored. Twelve spontaneously hypertensive rats (SHR), at 8 weeks old, were used in this study, and received either distilled water or atorvastatin for ten weeks, with age-matched normotensive Wistar-Kyoto rats (WKY) used as controls. RT-PCR and western blotting were used to detect the mRNA and protein expressions of phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), respectively, and a colorimetric method used to examine the SERCA2a activity. Additionally, cardiac hypertrophic indices, such as the cardiosomatic ratio, left ventricular weight to body weight (LVW/BW) ratio and cardiomyocytes transverse diameter (TDM), together with the systolic blood pressure (SBP) and serum lipids levels were also examined. After ten weeks, significant decreases were observed in both the mRNA and protein expression levels of SERCA2a, as well as its activity, in the hypertrophied hearts of the SHR. The administration of atorvastatin to the same strains of rats effectively inhibited these decreases, and the above cardiac hypertrophic indices, as well as the SBP and serum lipids levels were significantly decreased. However, no significant changes in the expressions of PLB were observed in WKY, SHR and atorvastatin-treated SHR. These findings demonstrated that through regulation of the PLB and SERCA2a levels in the hearts of SHR, atorvastatin can prevent the cardiac hypertrophy caused due to pressure overload, which provides a relatively new insight into the mechanism of atorvastatin in the prevention of cardiac hypertrophy.

CaMKII activates ASK1 and NF-kappaB to induce cardiomyocyte hypertrophy

Ca2+/calmodulin-dependent protein kinase (CaMK) is an important downstream target of Ca2+ in the hypertrophic signaling pathways. We previously showed that the activation of apoptosis signal-regulating kinase 1 (ASK1) or NF-kappaB is sufficient for cardiomyocyte hypertrophy. Infection of isolated neonatal cardiomyocytes with an adenoviral vector expressing CaMKIIdelta3 (AdCaMKIIdelta3) induced the activation of ASK1, while KN93, an inhibitor of CaMKII, inhibited phenylephrine-induced ASK1 activation. Overexpression of CaMKIIdelta3 induced characteristic features of in vitro cardiomyocyte hypertrophy. Infection of cardiomyocytes with an adenoviral vector expressing a dominant negative mutant of ASK1 (AdASK(KM)) inhibited the CaMKIIdelta3-induced hypertrophic responses. Overexpression of CaMKIIdelta3 increased the kappaB-dependent promoter/luciferase activity and induced IkappaBalpha degradation. Coinfection with AdCaMKIIdelta3 and AdASK(KM), and pre-incubation with KN93 attenuated CaMKIIdelta3- and phenylephrine-induced NF-kappaB activation, respectively. Expression of a degradation resistant mutant of IkappaBalpha inhibited CaMKIIdelta3-induced hypertrophic responses. These results indicate that CaMKIIdelta3 induces cardiomyocyte hypertrophy mediated through ASK1-NF-kappaB signal transduction pathway.

Cardiac-specific overexpression of a high Ca2+ affinity mutant of SERCA2a attenuates in vivo pressure overload cardiac hypertrophy

In cardiomyocytes, calcium plays important roles as a signal in cardiac hypertrophy and contraction-relaxation cycling. Elevation of Ca2+ concentration in myoplasm is associated with the onset and progression of hypertrophy as well as the enhancement of contractility. The cardiac Ca2+ ATPase (SERCA2a) of the sarcoplasmic reticulum plays a dominant role in lowering cytoplasmic calcium levels during relaxation and is regulated by phospholamban (PLN). To examine whether the modulation of SERCA2a activity results in the attenuation of cardiac hypertrophy and enhancement of contractility, we generated transgenic mice (TG) overexpressing a high calcium affinity SERCA2a mutant (K397/400E), lacking a functional association with PLN. In the TG hearts, the apparent affinity of SERCA2a for Ca2+ significantly increased compared with their nontransgenic littermate controls. The TG showed increased contraction and relaxation, with increases in the amplitude of Ca2+ transient and rapid Ca2+ decay. Upon induction of pressure overload by transverse aortic constriction, the TG developed less cardiac hypertrophy than littermate controls did. The activation of Ca2+-sensitive protein kinase C by pressure overload was significantly attenuated in the TG hearts. Our findings indicate an association of SERCA2a activity with cardiac hypertrophy and thus a new therapeutic target for the prevention and treatment of cardiac hypertrophy.

Blood pressure increase and incidence of hypertension in relation to inflammation-sensitive plasma proteins

OBJECTIVE

The reasons for the relationship between inflammation-sensitive plasma proteins (ISPs) and incidence of cardiovascular diseases are poorly understood. This study explored the hypothesis that ISPs are associated with future hypertension and age-related blood pressure increase.

METHODS AND RESULTS

Blood pressure and plasma levels of fibrinogen, alpha1-antitrypsin, haptoglobin, ceruloplasmin, and orosomucoid were determined in 2262 healthy men aged 35 to 50 years, initially without treatment for hypertension. The cohort was re-examined after 15.7 (+/-2.2) years. Incidence of hypertension and blood pressure increase was studied in relation to number of elevated proteins (ie, in the top quartile) at baseline. Among men without treatment for hypertension at follow-up, mean (+/-SD) increase in systolic blood pressure was 18.8+/-17, 19.2+/-17, 19.3+/-17, and 22.1+/-18 mm Hg, respectively, for men with 0, 1, 2, and > or =3 elevated proteins (P for trend=0.02, adjusted for confounders). The corresponding values for pulse pressure increase was 15.5+/-14, 15.8+/-14, 17.4+/-14, and 17.8+/-15 mm Hg, respectively (P=0.02). Incidence of hypertension (> or =160/95 mm Hg or treatment) and future blood pressure treatment showed similar associations with ISPs. Increase in diastolic blood pressure showed no association with ISPs.

CONCLUSIONS

Plasma levels of ISPs are associated with a future increase in blood pressure. This could contribute to the relationship between ISP levels and cardiovascular disease.

CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo

Hypertrophic growth is an adaptive response of the heart to diverse pathological stimuli and is characterized by cardiomyocyte enlargement, sarcomere assembly, and activation of a fetal program of cardiac gene expression. A variety of Ca(2+)-dependent signal transduction pathways have been implicated in cardiac hypertrophy, but whether these pathways are independent or interdependent and whether there is specificity among them are unclear. Previously, we showed that activation of the Ca(2+)/calmodulin-dependent protein phosphatase calcineurin or its target transcription factor NFAT3 was sufficient to evoke myocardial hypertrophy in vivo. Here, we show that activated Ca(2+)/calmodulin-dependent protein kinases-I and -IV (CaMKI and CaMKIV) also induce hypertrophic responses in cardiomyocytes in vitro and that CaMKIV overexpressing mice develop cardiac hypertrophy with increased left ventricular end-diastolic diameter and decreased fractional shortening. Crossing this transgenic line with mice expressing a constitutively activated form of NFAT3 revealed synergy between these signaling pathways. We further show that CaMKIV activates the transcription factor MEF2 through a posttranslational mechanism in the hypertrophic heart in vivo. Activated calcineurin is a less efficient activator of MEF2-dependent transcription, suggesting that the calcineurin/NFAT and CaMK/MEF2 pathways act in parallel. These findings identify MEF2 as a downstream target for CaMK signaling in the hypertrophic heart and suggest that the CaMK and calcineurin pathways preferentially target different transcription factors to induce cardiac hypertrophy.

The nuclear deltaB isoform of Ca2+/calmodulin-dependent protein kinase II regulates atrial natriuretic factor gene expression in ventricular myocytes

Cultured neonatal ventricular myocytes display features of myocardial hypertrophy including increased cell size, myofilament organization, and reexpression of the embryonic gene for atrial natriuretic factor (ANF). KN-93, an inhibitor of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase II), blocked the induction of these responses by the alpha1-adrenergic receptor agonist phenylephrine, whereas its inactive analog KN-92 did not. To directly determine whether CaM kinase II could regulate ANF gene expression, we transiently expressed each of three isoforms of CaM kinase II (alpha, deltaB, and deltaC) along with an ANF promoter/luciferase reporter gene. The deltaB isoform markedly increased luciferase gene expression, whereas comparable levels of the deltaC and alpha isoforms were ineffective. Expression of deltaB-CaM kinase II also potentiated phenylephrine-mediated ANF gene expression, and this effect was blocked by KN-93 but not by KN-92. The ability of deltaB-CaM kinase II to transactivate a truncated ANF promoter, containing a serum response element (SRE) required for phenylephrine-inducible gene expression, was lost when this SRE was mutated. The deltaB isoform of CaM kinase II has been shown to exhibit nuclear localization. Coexpression of the non-nuclear deltaC or alpha isoforms, which can form multimers with the deltaB isoform, prevented the nuclear localization of deltaB-CaM kinase II and also blocked its effects on ANF reporter gene and protein expression. In addition, a chimeric alpha-CaM kinase II which contains the nuclear localization signal of the deltaB isoform was able to induce ANF reporter gene expression, albeit to a lesser extent than deltaB-CaM kinase II. These data are the first to assign a function to the deltaB isoform of CaM kinase II and to link its nuclear localization to subsequent activation of cardiac gene expression.

Role of cAMP and calcium influx in endothelin-1-induced ANP release in rat cardiomyocytes

The mechanism of endothelin-1 (ET-1)-induced atrial natriuretic peptide (ANP) release was studied in neonatal rat ventricular cardiomyocytes. These cells expressed a single high-affinity class of ETA receptor (dissociation constant = 54 +/- 18 pM, n = 3), but no ETB receptors. Incubation of cardiomyocytes with ET-1 led to concentration-dependent ANP release and prostacyclin production. ET-1-induced ANP release was affected by neither protein kinase C (PKC) inhibition or downregulation nor by cyclooxygenase inhibition, indicating that ET-1-stimulated ANP secretion is not a PKC-mediated, prostaglandin-dependent process. Furthermore, ET-1 significantly stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production and increased cytosolic calcium concentration in these preparations. Both ET-1-induced calcium influx and ANP release were decreased by the cAMP antagonist Rp-cAMPS, the Rp diastereoisomer of cAMP. Moreover, ET-1-induced ANP secretion was strongly inhibited in the presence of nifedipine as well as in the absence of extracellular calcium. Thus our results suggest that ET-1 stimulates ANP release in ventricular cardiomyocytes via an ETA receptor-mediated pathway involving cAMP formation and activation of a nifedipine-sensitive calcium channel.

Mechanical strain increases expression of the brain natriuretic peptide gene in rat cardiac myocytes

Using a device that applies cyclical strain (1 Hz) to ventricular cardiocytes cultured on collagen-coated silicone elastomer surfaces, we have demonstrated strain-dependent increases in brain natriuretic peptide (BNP) secretion, BNP mRNA levels, and expression of a transiently transfected -1595 human BNP-luciferase reporter. When actinomycin D (10 microM) was introduced concomitantly with the strain stimulus, the strain-induced increase in BNP mRNA was eliminated, and the decay of transcripts was identical in the control and strained cells, indicating the lack of independent effects on transcript stability. Strain-dependent -1595 human BNP-luciferase activity was completely inhibited by chelerythrine, 2-aminopurine, genistein, and W-7 and only partially or not at all by KN-62, wortmannin, and H-89. The effects of these individual agents paralleled their effects on mitogen-activated protein kinase (MAPK) activity, but not c-Jun N-terminal kinase (JNK) activity, in the cells. Overexpression of wild-type MAPK and, to a lesser extent, JNK increased strain-dependent BNP promoter activity, whereas dominant-negative mutants of MAPK kinase, JNK kinase, or Ras completely blocked strain-dependent reporter activity. These findings provide the first demonstration that mechanical strain can increase myocardial gene expression through a transcriptional mechanism and suggest important roles for MAPK and JNK in mediating this effect.

Effects of lidocaine on atrial natriuretic peptide concentrations in plasma and urine

The antiarrhythmic agent lidocaine reduces inward sodium current and increases outward potassium current. Described studies investigated the effect of lidocaine on circulating and urinary levels of atrial natriuretic peptides in an intact canine model. Surface electrocardiography was monitored along with right ventricular, left ventricular and aortic pressures, and cardiac output. Plasma and urine atrial natriuretic peptides were measured immediately before and five minutes after a five minute, 2 mg/min, intravenous lidocaine infusion. Long acting natriuretic peptide (LANP), vessel dilator, and atrial natriuretic factor (ANF) were monitored by RIA. There were no measured hemodynamic or cardiomechanical changes noted after lidocaine infusion. Similarly, there was no change in plasma sodium or potassium, or urine sodium. There was, however, an increase in urine potassium levels. Additionally, plasma and urine LANP and ANF peptide levels were increased following lidocaine infusion, while plasma and urine concentrations of vessel dilator were not changed. These data suggest that lidocaine increases plasma and urine atrial natriuretic peptides by mechanisms other than cardiodepression and/or vasodilation.

Role of calcium in stretch-induced release and mRNA synthesis of natriuretic peptides in isolated rat atrium

To investigate the role of Ca2+ in stretch-induced synthesis and release of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) isolated superfused rat atria were stretched by raising intra-atrial pressure. The immunoreactive (ir-) ANP and BNP concentrations were analysed by radioimmunoassay and the corresponding mRNA levels were quantified by Northern blot and dot blot analyses. Stretch-induced ir-ANP release and a rise in BNP mRNA levels increased at high (3.0 mM) compared to low (0.5 mM) extracellular Ca2+ concentration ([Ca2+]o). Moreover, the adaptation of stretch-induced ir-ANP release was dependent on [Ca2+]o. Atrial BNP mRNA levels were increased by stretch also in non-paced, electrically silent atria, where voltage-activated Ca2+ channels are not activated. The stretch-induced rise in BNP mRNA was blocked by gadolinium (80 microM), but not by the L-type channel blocker diltiazem (3.0 microM). This study indicates that both the stretch-secretion coupling of ir-ANP release and the pressure-stimulated synthesis of BNP mRNA are Ca2+-dependent processes. Gadolinium inhibits the stretch-stimulated rise in BNP mRNA levels in contracting and non-contracting atria, which is similar to its ability to block stretch-activated ir-ANP release, suggesting the involvement of Ca2+-permeable stretch-activated channels.

Circadian relationships between circulating atrial natriuretic peptides and serum calcium and phosphate in healthy humans

Long-acting natriuretic peptide (LANP), vessel dilator (VSDL), and atrial natriuretic factor (ANF) consisting of amino acids (aa) 1 to 30, 31 to 67, and 99 to 126, respectively, of the 126-aa ANF prohormone circulate in humans. Among the biologic properties of these peptides is the ability of ANF to decrease intracellular calcium concentrations. To determine if atrial natriuretic peptides are directly related to serum calcium and/or phosphate in healthy normocalcemic humans, we examined 21 24-hour profiles of VSDL, LANP, ANF, and serum calcium and phosphate in 14 healthy humans. VSDL, LANP, and ANF each had significant (P < .001) circadian rhythms, with peak concentrations late during sleep (at 4:00 AM) being nearly twice the concentrations in the afternoon and evening. Serum calcium and phosphate also had significant circadian rhythms (P < .001) with troughs nearly opposite to those of the atrial natriuretic peptides, suggesting that atrial peptides may be important in the modulation of the circadian rhythms of calcium and phosphate. The nearly identical circadian rhythms of the atrial natriuretic peptides and of parathyroid hormone (PTH) reported by others, along with evidence that PTH may increase atrial peptide release, suggest that some of the effects attributed to PTH may be mediated by atrial natriuretic peptides.

Renal artery stenosis rapidly enhances atrial natriuretic peptide gene expression

The aim of this study was to examine the influence of the systemic renin-angiotensin system on the gene expression of atrial natriuretic peptide in rat hearts. The renin-angiotensin system was stimulated (1) by unilateral renal artery clipping (0.2-mm clip, 2 days), producing a fourfold increase of circulating plasma renin activity and increasing blood pressure; (2) by furosemide infusion with simultaneous salt substitution, increasing plasma renin activity values to 45 ng angiotensin I/h per milliliter without changing blood pressure; or (3) by administration of the calcium antagonist amlodipine, which increased plasma renin activity values to 42 ng angiotensin I/h per milliliter and lowered blood pressure. Unilateral renal artery clipping increased atrial natriuretic peptide mRNA levels approximately 20-fold in the left ventricles and approximately twofold in the right ventricles and atria. Furosemide infusion had no effect on cardiac atrial natriuretic peptide mRNA levels, and in amlodipine-treated rats, cardiac atrial natriuretic peptide mRNA levels decreased to 30% of control values. The increase of atrial natriuretic peptide mRNA in the ventricles during renal artery clipping was blunted by the administration of the angiotensin-converting enzyme inhibitor ramipril, which also attenuated the blood pressure rise. In clipped rats amlodipine did not change elevated plasma renin activity values but abolished the rise of blood pressure and also attenuated the rise of atrial natriuretic peptide mRNA in the hearts. These findings indicate that an increase of the activity of the systemic renin-angiotensin system does not result in an obligatory change in cardiac atrial natriuretic peptide gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

The dihydropyridine calcium channel blocker BAY t 7207 attenuates the exercise induced increase in plasma ANF and cyclic GMP in patients with mildly impaired left ventricular function

In man, chronic antihypertensive calcium antagonist treatment improves cardiac function and reduces plasma ANF concentrations. Physical exercise increases cardiac workload and plasma ANF levels. In the present study, we investigated the effects of acute administration of the dihydropyridine calcium antagonist BAY t 7207 (BAY) during bicycle exercise on plasma ANF and plasma cyclic GMP levels, on mean arterial pressure (MAP), heart rate (HR), and on natriuresis and urinary urodilatin excretion. In a randomized, double-blind placebo controlled cross-over trial, 8 patients (age 56.8 +/- 2.5 y) with documented coronary artery disease and mildly impaired left ventricular function (EF 50.0 +/- 1.3%), received oral BAY (20 mg) or placebo. Forty-five minutes after medication, patients underwent a standardised exercise bicycle test in the supine position (6 min 25 W, 6 min 50 W). Before exercise, MAP was lower after BAY (88.8 +/- 4.1 mmHg) than after placebo (95.7 +/- 3.5 mmHg; p = 0.024), and HR was higher after BAY (76.8 +/- 3.5 bpm) than after placebo (69.5 +/- 3.6 bpm; p = 0.049). Plasma ANF tended to be higher after BAY (31.2 +/- 5.6 pg/ml) than after placebo (26.7 +/- 5.0 pg/ml), and plasma cGMP was not different (BAY 3.4 +/- 0.3, placebo 3.8 +/- 0.3 pmol/ml). During exercise, the relative increases in HR (+43%) and MAP (+17%) were identical after BAY and placebo. In contrast, ANF levels during exercise increased by 130 +/- 28% after placebo but only by 36 +/- 11% after BAY (p = 0.011). In parallel, plasma cyclic GMP increased by 61 +/- 13% after placebo and by 20 +/- 8% after BAY (p = 0.013). At the end of exercise, the BAY-induced reduction in plasma cyclic GMP reflected the reduction in diastolic arterial pressure (r = 0.717; p = 0.045). Compared to placebo, BAY treatment increased the fractional excretion rate of sodium from 0.46 +/- 0.11 to 0.90 +/- 0.22% (p = 0.016), without relation to urinary urodilatin excretion. Thus, the calcium antagonist BAY t 7207 attenuated the exercise-induced increase in plasma ANF and cyclic GMP probably due to its vasodilator effect. The relationship between blood pressure and the ANF system during exercise, which parallels findings during chronic antihypertensive treatment, may open a perspective for early evaluation of long-term therapy with calcium channel blockers.

Effect of extracellular calcium depletion on the two-step ANP secretion in perfused rabbit atria

Employing isolated perfused rabbit atrial model we have found that stretch-activated atrial natriuretic peptide (ANP) secretion takes place in two steps: release of ANP from myocytes into surrounding intercellular space, and then translocation of the released ANP into atrial lumen along with the extracellular fluid (ECF) translocated upon releasing the stretch. Ca2+, one of the most important factors regulating secretory processes, has been reported by many workers to have influence on the ANP secretion, but at large variance. In the present study, therefore, we undertook to clarify the influence of Ca2+ depletion on ANP secretion and further to define which of the two steps is affected by Ca2+ removal. Extracellular Ca2+ depletion resulted in increased basal secretion and in accentuated secretion of immunoreactive (ir) ANP in response to mechanical stimuli. The translocation of ECF increased in response to atrial stretch-and-release, but it was not affected by Ca2+ depletion. The irANP concentration in the extracellular space calculated as the amount of irANP secreted in relation to the ECF translocated significantly increased when extracellular Ca2+ was depleted. These results indicate that extracellular Ca2+ depletion accentuates the stretch-induced ANP secretion through the augmentation of ANP release into the interstitium without changes in the ECF translocation.

Polyamine regulation of atrial natriuretic peptide in cultured cardiocytes

In the following investigation, we have studied the role of polyamines in the regulation of atrial natriuretic peptide (ANP) using ventricular cardiocytes which in culture synthesize and secrete ANP. Polyamines are cellular cations ubiquitous in eukaryotes, and ANP is a hormone synthesized and secreted by the cardiac atria in adult animal. The cardiocytes were isolated from neonatal rat hearts by enzymatic dissociation using trypsin and collagenase. The functional role of polyamines in regulation of ANP was assessed by exposing the cardiocytes to difluoromethylornithine (DFMO) which is an inhibitor of ornithine decarboxylase, an initial rate-limiting enzyme in the biosynthesis of polyamines. The results showed that DFMO reduced the levels of putrescine (diamine) and spermidine (triamine) in cultured cardiocytes, and it decreased the levels of ANP in media and cellular extracts of cardiocytes as a function of its dose. An addition of putrescine (100 microM) restored within 5-15 min the levels of ANP in media of both control and polyamine-depleted cardiocytes. These results suggest that polyamines are one of the cellular factors involved in regulation of ANP secretion in cultured cardiocytes.

Effects of genistein on cardiac contractile force and atrial natriuretic peptide secretion in the isolated perfused rat heart

We examined the effects of a selective protein tyrosine kinase inhibitor, the isoflavonoid genistein, on haemodynamics and atrial natriuretic peptide (ANP) secretion in perfused rat heart preparations. The addition of genistein into the perfusion fluid at concentrations of 11, 22 and 37 microM for 30 min in the spontaneously beating rat hearts caused dose-dependent, sustained increases in contractile force, perfusion pressure and immunoreactive ANP secretion, while heart rate remained constant. The positive inotropic and vasoconstrictor effects of genistein were significantly (P < 0.001) greater in the paced than in spontaneously beating rat hearts. Infusion of the calcium-channel antagonist diltiazem (3 microM) inhibited the genistein-induced positive inotropic effect by 52% (P < 0.001), and KN-62 (1.5 microM), an inhibitor of Ca2+/calmodulin-dependent protein kinase II, by 34% (P < 0.001). The genistein-induced increase in immunoreactive ANP secretion was completely blocked by diltiazem (P < 0.001) while KN-62 delayed (P < 0.02) the increase of immunoreactive ANP concentration in the perfusate. These results show that genistein, at concentrations known to inhibit the activities of protein tyrosine kinases, dose-dependently increased contractile force, coronary vascular tone and ANP secretion from isolated perfused rat hearts. These cardiac effects of genistein may be mediated by elevation of intracellular Ca2+ concentration, as shown by the inhibition of inotropic and secretory effects by both L-type calcium channel antagonist and Ca2+/calmodulin-dependent protein kinase inhibitor.

Basal and acidic fibroblast growth factor-induced atrial natriuretic peptide gene expression and secretion is inhibited by staurosporine

We examined the mechanisms involved in the activation of atrial natriuretic peptide (ANP) gene expression and secretion in response to acidic fibroblast growth factor (aFGF) by studying the effects of staurosporine, a protein kinase C inhibitor, and 12-O-tetradecanoyl phorbol 13-acetate (TPA), an activator of protein kinase C, on basal and AFGF-induced ANP messenger RNA (mRNA) and immunoreactive ANP (IR-ANP) levels in cultured neonatal rat cardiac myocytes. Acidic FGF caused a dose- and time-dependent increase in IR-ANP and immunoreactive N-terminal fragment of proANP (IR-NT-proANP) release into the culture medium from ventricular but not from atrial myocytes. In ventricular cells, 50 ng/ml aFGF for 24 or 48 h resulted in a 70% or 181% increase, respectively, in the accumulation of IR-ANP into the culture medium. Acidic FGF also stimulated ANP gene expression significantly; after 48 h of incubation, the ANP mRNA levels of aFGF-treated ventricular myocytes were 205% (P < 0.001) higher than those of control cells. Staurosporine alone at concentration of 10 nM significantly decreased the basal IR-ANP and IR-NT-proANP secretion, and inhibited the aFGF-induced increase in ANP mRNA and IR-ANP levels in ventricular myocytes. TPA (100 nM) alone significantly stimulated ANP gene expression and secretion but these effects were not augmented by combining aFGF with TPA. High performance liquid chromatographical analysis showed that atrial and ventricular myocytes maintained in serum-free medium were capable of secreting processed, ANP99-126 sized material, and that aFGF did not alter the processing of ANP in ventricular cultures. These results demonstrate that aFGF is a potent stimulator of ANP gene expression and secretion in cultured neonatal rat ventricular but not in atrial cells. The observations that (a) staurosporine completely abolished the effects of aFGF on ANP gene expression and release and (b) ANP secretory and gene expression inducing effects of phorbol ester were not augmented by aFGF, suggest an important role of protein kinase C in mediating aFGF-induced ANP gene expression and secretion.

Atrial natriuretic peptide and cyclic guanosine-3'5'-monophosphate in hypertensive pregnancy and during nifedipine treatment

Atrial natriuretic peptide exhibits natriuretic, diuretic and vasodilatory properties. We compared plasma concentrations of atrial natriuretic peptide, cyclic guanosine-3',5'-monophosphate (cGMP), electrolytes and urinary excretion of cGMP and electrolytes in hypertensive pregnant women to those in normotensive pregnant and normotensive non-pregnant women. Plasma atrial natriuretic peptide concentrations in hypertensive pregnant and normotensive non-pregnant women were equal, whereas in normotensive pregnant women it was lower (P < 0.05), than in non-pregnant. Urinary cGMP excretion was higher in both normotensive and hypertensive pregnant than in non-pregnant women (P < 0.01), whereas plasma cGMP levels were similar. A five-day nifedipine treatment (10 mg t.i.d.) had no effects on any of the variables. In hypertensive pregnancy, a reduction of systolic blood pressure by nifedipine correlated with the initial plasma atrial natriuretic peptide (P < 0.05) and a decrease in diastolic blood pressure with the initial plasma cGMP concentration (P < 0.05). The results of this small material suggest that plasma atrial natriuretic peptide concentration predicts the response to nifedipine in hypertensive pregnancy. However, the atrial natriuretic peptide-cGMP system does not seem to mediate the antihypertensive effect of nifedipine, while plasma atrial natriuretic peptide remained unaltered. Increased urinary cGMP excretion in both pregnant groups but lowered plasma atrial natriuretic peptide in normotensive pregnancy suggest other factors than circulating atrial natriuretic peptide to promote renal cGMP excretion during pregnancy.

Regulation of hypertrophy and atrophy in cultured adult heart cells

Mechanical loading and alpha-adrenergic receptor stimulation have both been shown to induce hypertrophy in isolated neonatal heart cells. The present study examined the effects of adrenergic hormones and contractile activity on the hypertrophic response in isolated adult feline cardiomyocytes maintained for more than 14 days in insulin- and serum-supplemented medium. Measurements of the hypertrophic response included cell size, total protein content, myosin heavy chain content, and the time course of activation of increased protein synthesis. Reactivation of the "fetal" gene program was evaluated by secretion of atrial natriuretic factor (ANF) into the medium. Significant myocyte hypertrophy was induced in both quiescent myocytes treated with alpha 1-adrenergic agonists and in beating myocytes treated with beta-adrenergic agonists. However, there were both quantitative and qualitative differences in the response to each type of stimulation. alpha-Adrenergic agonists promoted an increase in cell size, protein content, and ANF secretion but not myofibrillar reorganization, which was observed only in beating myocytes. In contrast to results reported for neonatal heart cells, determinants of hypertrophy in beating myocytes exceeded those in nonbeating alpha 1-adrenergic agonist-treated heart cells in every parameter examined. In addition, in the case of both beating and alpha-adrenergic stimulation, there were marked time-dependent variations in rates of protein synthesis over the interval of 4 hours to 7 days of treatment with each type of stimulus. Differences were also encountered in correlations between rates of protein synthesis and protein accumulation over this interval. The effect of beating was particularly important both to the reorganization of myofibrillar structure and the metabolism of myosin heavy chain. In cultures in which beating was inhibited with the calcium channel antagonist nifedipine, the loss of myosin heavy chain was significantly greater than that of total protein.

Cellular mechanisms for synthesis and secretion of atrial natriuretic peptide and brain natriuretic peptide in cultured rat atrial cells

To investigate the cellular mechanism for the synthesis and secretion of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), we examined the effects of vasoactive agents on the secretion rates and gene expression of ANP and BNP in cultured rat atrial cells. Endothelin (10(-7) M, +61%), 12-O-tetradecanoylphorbol 13-acetate (TPA, 10(-6) M, +62%), the calcium ionophore A23187 (10(-6) M, +95%), and Bay K 8644 (10(-6) M, +34%) (p < 0.05 each) all increased the secretion of ANP into the culture media in a dose-dependent fashion. On the other hand, endothelin (10(-7) M, +57%) and TPA (10(-6) M, +55%) (p < 0.01 each) increased the secretion of BNP in a dose-dependent manner, whereas A23187 (10(-6) M, -45%, p < 0.001) suppressed the secretion of BNP in a dose-dependent manner, and Bay K 8644 caused no significant effects on BNP secretion. The molecular forms of intracellular ANP were exclusively gamma-ANP, whereas those of BNP were gamma-BNP and its carboxy terminal 45-amino-acid peptide, BNP-45. The ratio of media to cell contents was much higher in BNP than in ANP. Northern blot analysis revealed that both ANP mRNA and BNP mRNA levels were significantly increased by 10(-7) M endothelin (ANP mRNA, +52%; BNP mRNA, +36%; p < 0.05 each) and 5 x 10(-5) M 1-oleoyl-2-acetylglycerol (ANP mRNA, +296%; BNP mRNA, +133%; p < 0.01 each) but not by 10(-6) M A23187. Thus, the secretion of ANP is stimulated by both the elevation of [Ca2+]i and the activation of protein kinase C, whereas its synthesis is increased mainly by the activation of protein kinase C. The synthesis and secretion of BNP are augmented by the activation of protein kinase C rather than the elevation of [Ca2+]i. Furthermore, the processing and secretion of ANP and BNP may be regulated in different manners.

Stretch-dependent regulation of atrial peptide synthesis and secretion in cultured atrial cardiocytes

We have developed a novel system to study stretch-dependent secretion of atrial natriuretic peptide (ANP) using cultured neonatal rat atriocytes in vitro. Application of tension (i.e., 2 sequential stretches) to cells grown on a flexible culture surface effected a dose-dependent increase in immunoreactive (ir) ANP release into the medium. Analysis of atriocyte cytoplasmic RNA 24 h poststretch revealed an increase in ANP mRNA levels of about ninefold relative to the unstretched controls. Medium ATP levels, measured as an index of cellular damage, were similar in control and stretched cells. Furthermore, cooling the cultures to 0 degrees C suppressed both basal as well as stretch-stimulated release. These findings argue against cellular damage and nonspecific release of irANP as an explanation for the increase in medium immunoreactivity. Stretch was incapable of amplifying the secretory response to prostaglandin F2 alpha, suggesting possible overlap in the pathways whereby these stimuli effect release of the peptide. The calcium channel blocker verapamil had no effect on stretch-dependent irANP release, whereas calmidzolium, a calmodulin inhibitor, suppressed basal as well as stretch-dependent secretion, implying a potentially important relationship between intracellular calcium metabolism and irANP release.

Conserved mechanism of negative gene regulation by extracellular calcium. Parathyroid hormone gene versus atrial natriuretic polypeptide gene

We found that a negative calcium-responsive element (nCaRE) originally reported in the human parathyroid hormone gene is conserved among several genes. The results of the present study show that expression of one of the genes, the rat atrial natriuretic polypeptide gene, was negatively regulated in the heart by extracellular calcium by using an in vivo infusion system. Moreover, transfection of the cultured cells revealed that this DNA element conferred negative regulation by extracellular calcium on the reporter gene. It is suggested that there is a gene family whose expression is negatively regulated by extracellular calcium through this conserved DNA motif, nCaRE.

Divergent regulation of the human atrial natriuretic peptide gene by c-jun and c-fos

Employing transient transfection analysis in neonatal rat cardiocytes, we have demonstrated that overexpression of c-jun results in a dose-dependent induction of the human atrial natriuretic peptide (hANP) gene promoter. Studies using a series of mutations in the hANP gene promoter identified a TRE-like, cis-acting regulatory sequence which conferred c-jun sensitivity. This same region was shown to interact with the c-jun/c-fos complex in an in vitro gel mobility shift assay. Selective mutation of this site suppressed basal activity of the hANP promoter and significantly reduced c-jun-dependent activation. Overexpression of c-fos had a biphasic effect on hANP gene promoter activity. At low levels, in concert with c-jun, it activated, while at higher levels it suppressed, transcription from the hANP gene promoter. This inhibition was both cell and promoter specific. hANP gene promoter sequences which mediate c-fos-dependent inhibition appear to be separable from those responsible for the induction. In addition, the protein domains on c-fos responsible for transcriptional activation and repression can be segregated topographically, with the inhibitory activity being localized to the carboxy-terminal domain. Thus, c-fos can activate or repress hANP gene expression through two separate functional domains that act on distinct regulatory elements in the hANP gene promoter. These data imply that the ANP gene may be a physiological target for c-fos- and c-jun-dependent activity in the heart and suggest a potential mechanism linking environmental stimuli to its expression.

Divergent regulation of the human atrial natriuretic peptide gene by c-jun and c-fos

Employing transient transfection analysis in neonatal rat cardiocytes, we have demonstrated that overexpression of c-jun results in a dose-dependent induction of the human atrial natriuretic peptide (hANP) gene promoter. Studies using a series of mutations in the hANP gene promoter identified a TRE-like, cis-acting regulatory sequence which conferred c-jun sensitivity. This same region was shown to interact with the c-jun/c-fos complex in an in vitro gel mobility shift assay. Selective mutation of this site suppressed basal activity of the hANP promoter and significantly reduced c-jun-dependent activation. Overexpression of c-fos had a biphasic effect on hANP gene promoter activity. At low levels, in concert with c-jun, it activated, while at higher levels it suppressed, transcription from the hANP gene promoter. This inhibition was both cell and promoter specific. hANP gene promoter sequences which mediate c-fos-dependent inhibition appear to be separable from those responsible for the induction. In addition, the protein domains on c-fos responsible for transcriptional activation and repression can be segregated topographically, with the inhibitory activity being localized to the carboxy-terminal domain. Thus, c-fos can activate or repress hANP gene expression through two separate functional domains that act on distinct regulatory elements in the hANP gene promoter. These data imply that the ANP gene may be a physiological target for c-fos- and c-jun-dependent activity in the heart and suggest a potential mechanism linking environmental stimuli to its expression.

Annexins V and VI: major calcium-dependent atrial secretory granule-binding proteins

Atrial natriuretic peptide is stored by atrial myocytes in secretory granules, known as atrial specific granules, and is released from these granules by exocytosis. We have isolated a group of atrial proteins by affinity chromatography that bind to atrial specific granules in a calcium-dependent manner. The two major proteins isolated (32.5 kd and 67 kd) are calcium-binding proteins and have been identified as annexins V and VI by immunoblotting with specific antisera. The calcium dependence of their binding to atrial specific granules has been characterized in vitro and indicates that this interaction takes place at micromolar levels of calcium. In addition, the group of proteins isolated includes another calcium-binding protein of 20 kd, as well as GTP-binding proteins of 22 to 26 kd. Membrane interactions during exocytosis are presumably mediated by the interaction of specific proteins with the granule membrane. The properties of the proteins described here, and their ability to bind to atrial specific granules in a calcium-dependent manner, make them likely candidates in the search for regulatory proteins mediating atrial natriuretic peptide secretion.

Proximal regulatory domains of rat atrial natriuretic factor gene

BACKGROUND

At least three cis-acting regulatory elements are required for expression of the rat atrial natriuretic factor (ANF) gene. One distal cis-acting regulatory element lies more than 640 base pairs from the transcription initiation site.

METHODS AND RESULTS

In this report, we identify two other proximal regulatory elements that lie within 609 base pairs of the transcription initiation site. One proximal regulatory element contains an activator protein-1 (AP-1)-like binding site and is recognized by the AP-1 protein, the c-fos/c-jun proto-oncogene heterodimer in vitro. The second regulatory element contains a cyclic AMP-responsive element (CRE)-like recognition site.

CONCLUSIONS

In vitro binding of the c-fos/c-jun heterodimer to ANF gene sequences suggests that the heterodimer may play a role in the regulation of gene transcription in vivo. This observation may also explain the correlation between c-fos/c-jun expression and ventricular ANF gene expression found in hypertrophic states. Nuclear extracts from normal cardiocytes contain proteins that bind these regulatory elements but do not appear to bind at the AP-1 site, suggesting that the levels of fos/jun heterodimer in nonhypertrophied cardiocytes are quite low.

Endothelin increases the synthesis and secretion of atrial natriuretic peptide in neonatal rat cardiocytes

Endothelin (ET) effected a dose-dependent increment in atrial natriuretic peptide (ANP) secretion and ANP mRNA accumulation in neonatal rat atrial and ventricular cardiocytes but had no effect on the processing of the ANP prohormone to the mature ANP product. The secretagogue effect was not limited by cell density. Both basal and ET-dependent secretory activity were abrogated by the calmodulin antagonist calmidazolium but were unaffected by meclophenamate or pertussis toxin. The magnitude of the ET-dependent increment in ANP secretion was amplified by culturing the cells in a dynamically pulsating (vs. static) environment, implying an interaction between mechanical and agonist-mediated secretory stimuli in this system. ET also promoted immunoreactive ANP release from primary cultures of fetal rat hypothalamic cultures, suggesting that this regulatory function may be generally employed in ANP gene-expressing cells. These findings demonstrate that ET has parallel effects on ANP synthesis and secretion and support a role for this peptide in the regulation of local and circulating levels of the natriuretic hormone.