Decreased bioactivity of the guanine nucleotide-binding protein that stimulates adenylate cyclase in hearts from cardiomyopathic Syrian hamsters.

We investigated regulation of cardiac adenylate cyclase in 29-d-old BIO 14.6 Syrian hamsters, which inherit cardiomyopathy as an autosomal recessive trait. Pharmacologic stimulation of adenylate cyclase in cardiac membranes with isoproterenol, fluoride ion, guanine nucleotide, forskolin, and manganous ion indicated that there was defective coupling of the guanine nucleotide-binding protein that stimulates adenylate cyclase (Gs) to adenylate cyclase. Cyc complementation assays revealed congruent to 50% less Gs activity in cardiac and skeletal muscle from cardiomyopathic hamsters. Despite this decrease in functional Gs, there were no changes in immunologic levels of the alpha-subunit of Gs (alpha Gs) or in levels of mRNA encoding alpha Gs. The defect in Gs bioactivity was limited to cardiac and skeletal muscle, occurred only in animals homozygous for the dystrophic trait, and was demonstrable before any cardiac abnormalities were evident on light microscopy. By contrast, cardiac levels of beta-adrenergic receptors were not different in cardiac membranes from BIO 14.6 hamsters. We conclude that a functional defect in alpha Gs may contribute to a contractile abnormalities in the cardiomyopathic BIO 14.6 hamster. However, the etiology of the alpha Gs defect remains obscure.

Identification of hyponatremia as a risk factor for the development of functional renal insufficiency during converting enzyme inhibition in severe chronic heart failure.

To identify patients with severe chronic heart failure who are at greatest risk of developing functional renal insufficiency during converting enzyme inhibition, creatinine clearance was measured in 59 patients before and after long-term therapy with captopril (39 patients) or enalapril (20 patients), while digitalis and diuretic therapy was kept constant. Creatinine clearance increased or remained constant in 33 of the 59 patients (Group I), but declined in the remaining 26 patients (Group II). The two groups were similar with respect to the cause of heart failure, pretreatment renal function and all pretreatment hemodynamic variables. Patients in Group II, however, had lower values for serum sodium concentration (134.8 +/- 1.0 versus 137.0 +/- 0.6 mmol/liter) and higher values for plasma renin activity (10.6 +/- 3.4 versus 3.0 +/- 0.5 ng/ml per hour), received larger doses of furosemide (108 +/- 11 versus 84 +/- 6 mg/day), were more frequently diabetic (42 versus 15%) and were more frequently treated with enalapril (50 versus 21%) than were patients in Group I (all p less than 0.05). By stepwise logistic analysis, only hyponatremia (or an elevated plasma renin activity) and enalapril therapy independently predicted the decline in creatinine clearance during converting enzyme inhibition. These observations could not be explained by changes in systemic blood pressure. In patients with a normal serum sodium concentration (greater than or equal to 137 mmol/liter), creatinine clearance increased with captopril (+21%, p less than 0.05), but not with enalapril (-6%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic importance of the immediate hemodynamic response to nifedipine in patients with severe left ventricular dysfunction.

To determine the clinical significance of the occurrence of hemodynamic deterioration after the administration of calcium channel blocking drugs, nifedipine (20 mg orally) was administered to 29 patients with severe left ventricular dysfunction. Thirteen patients showed hemodynamic improvement with the drug (Group 1), as shown by a notable increase in cardiac index associated with a modest decrease in mean arterial pressure. The other 16 patients exhibited hemodynamic deterioration after nifedipine (Group 2), as reflected by a decline in right and left ventricular stroke work indexes accompanied by a marked hypotensive response. These differences were not related to differences in the peripheral vascular response to nifedipine, because both groups showed similar decreases in systemic and pulmonary vascular resistances. Groups 1 (hemodynamic improvement) and 2 (hemodynamic deterioration) were similar with respect to all demographic variables and pretreatment left ventricular performance (cardiac index, left ventricular filling pressure and systemic vascular resistance). Yet, the 1 year actuarial survival in patients in Group 1 was substantially better than that in patients in Group 2 (67 versus 23%, p = 0.009). Group 2, however, had higher values for plasma renin activity (17.7 +/- 6.0 versus 4.3 +/- 1.4 mg/ml per h, p less than 0.05), lower values for serum sodium concentration (134.6 +/- 1.2 versus 139.2 +/- 0.6 mEq/liter, p less than 0.05) and higher values for mean right atrial pressure (15.8 +/- 2.0 versus 7.9 +/- 1.4 mm Hg, p less than 0.01) than did patients in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Intercellular transfer of the virally derived precursor form of acid alpha-glucosidase corrects the enzyme deficiency in inherited cardioskeletal myopathy Pompe disease.

Pompe disease is a lethal cardioskeletal myopathy in infants and results from genetic deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). Genetic replacement of the cDNA for human GAA (hGAA) is one potential therapeutic approach. Three months after a single intramuscular injection of 10(8) plaque-forming units (PFU) of E1-deleted adenovirus encoding human GAA (Ad-hGAA), the activity in whole muscle lysates of immunodeficient mice is increased to 20 times the native level. Direct transduction of a target muscle, however, may not correct all deficient cells. Therefore, the amount of enzyme that can be transferred to deficient cells from virally transduced cells was studied. Fibroblasts from an affected patient were transduced with AdhGAA, washed, and plated on transwell culture dishes to serve as donors of recombinant enzyme. Deficient fibroblasts were plated as acceptor cells, and were separated from the donor monolayer by a 22-microm pore size filter. Enzymatic and Western analyses demonstrate secretion of the 110-kDa precursor form of hGAA from the donor cells into the culture medium. This recombinant, 110-kDa species reaches the acceptor cells, where it can be taken up by mannose 6-phosphate receptor-mediated endocytosis. It then trafficks to lysosomes, where Western analysis shows proteolytic processing to the 76- and 70-kDa lysosomal forms of the enzyme. Patient fibroblasts receiving recombinant hGAA by this transfer mechanism reach levels of enzyme activity that are comparable to normal human fibroblasts. Skeletal muscle cell cultures from an affected patient were also transduced with Ad-hGAA. Recombinant hGAA is identified in a lysosomal location in these muscle cells by immunocytochemistry, and enzyme activity is transferred to deficient skeletal muscle cells grown in coculture. Transfer of the precursor protein between muscle cells again occurs via mannose 6-phosphate receptors, as evidenced by competitive inhibition with 5 mM mannose 6-phosphate. In vivo studies in GAA-knockout mice demonstrate that hepatic transduction with adenovirus encoding either murine or human GAA can provide a depot of recombinant enzyme that is available to heart and skeletal muscle through this mechanism. Taken together, these data show that the mannose 6-phosphate receptor pathway provides a useful strategy for cell-to-cell distribution of virally derived recombinant GAA.

Hormone-electrolyte interactions in the pathogenesis of lethal cardiac arrhythmias in patients with congestive heart failure. Basis of a new physiologic approach to control of arrhythmia.

Congestive heart failure is the most arrhythmogenic disorder in cardiovascular medicine. As left ventricular performance deteriorates and symptoms of dyspnea and fatigue become progressively more severe, nearly all patients with heart failure experience frequent and complex ventricular tachyarrhythmias and nearly half die suddenly during long-term follow-up. This imminent risk of sudden death appears to be present for all patients with congestive heart failure; ambulatory electrocardiographic monitoring and programmed electrical stimulation are not useful in distinguishing patient subsets that are particularly predisposed to fatal arrhythmic events. Although conventional antiarrhythmic agents are widely prescribed as a nonspecific approach to prevent sudden death in these patients, there is little evidence to indicate that these drugs possess clinically important antiarrhythmic activity in patients with congestive heart failure, and these agents frequently serve to exacerbate the heart failure state and the underlying ventricular tachyarrhythmia. A useful approach to the prevention of sudden death in patients with congestive heart failure addresses the reversible causes of lethal ventricular arrhythmias in these individuals. Both experimental and clinical evidence indicates that circulating neurohormones and electrolyte deficits (particularly of potassium and magnesium) interact to provoke malignant ventricular ectopic rhythms and that the prevention of electrolyte depletion and the use of neurohormonal antagonists may exert clinically important antiarrhythmic actions. This physiologic approach may prove to be a more effective means of ameliorating the problem of sudden death than the empiric administration of conventional antiarrhythmic drugs.

Influence of diabetes mellitus on changes in left ventricular performance and renal function produced by converting enzyme inhibition in patients with severe chronic heart failure.

Diabetes mellitus is frequently accompanied by specific abnormalities of the renin-angiotensin system, but it is not known whether these alterations modify the response to converting enzyme inhibition. To evaluate this possibility, 129 patients with severe chronic heart failure were treated with captopril or enalapril for one to three months, while doses of digoxin and diuretics were kept constant; 35 patients had diabetes mellitus. Prior to therapy, diabetic patients had lower plasma renin activity (3.4 +/- 0.5 versus 7.0 +/- 1.1 ng/ml/hour) than did nondiabetic control subjects (p less than 0.05); yet the initial hemodynamic response to captopril was similar in both groups. Plasma renin activity predicted the hypotensive response to the first dose of captopril in nondiabetic control subjects (r = 0.70, p less than 0.001) but not in diabetic patients (r = 0.29). During long-term treatment with captopril or enalapril, both diabetic and nondiabetic patients had similar increases in cardiac index and decreases in mean arterial pressure and systemic vascular resistance. Diabetic patients, however, showed larger reductions in left ventricular filling pressure (-13.8 versus -9.1 mm Hg, p less than 0.02) and mean right atrial pressure (-6.2 versus -3.9 mm Hg, p less than 0.05) than did nondiabetic subjects; this was accompanied by a notable decline in body weight in diabetic patients only. Renal function remained unaltered during converting enzyme inhibition in nondiabetic patients, but deteriorated significantly in diabetic patients, as reflected by a marked increase in serum creatinine concentration (1.7 +/- 0.1 to 2.1 +/- 0.1 mg/dl, p less than 0.001). In conclusion, despite lower pretreatment plasma renin activity, diabetic patients with severe chronic heart failure demonstrated improvement during long-term converting enzyme inhibition to a degree similar to (if not greater than) that seen in nondiabetic control subjects, but were more susceptible to the development of functional renal insufficiency than their nondiabetic counterparts. These differences are explicable by abnormalities of renin/aldosterone synthesis and angiotensin-mediated vasoregulation that are known to be present in the diabetic state.

Arterial delivery of genetically labelled skeletal myoblasts to the murine heart: long-term survival and phenotypic modification of implanted myoblasts.

The ability to replace damaged myocardial tissue with new striated muscle would constitute a major advance in the treatment of diseases that irreversibly injure cardiac muscle cells. The creation of focal grafts of skeletal muscle has been reported following the intramural injection of skeletal myoblasts into both normal and injured myocardium. The goals of this study were to determine whether skeletal myoblast-derived cells can be engrafted into the murine heart following arterial delivery. The murine heart was seeded with genetically labeled C2C12 myoblasts introduced into the arterial circulation of the heart via a transventricular injection. A transventricular injection provided access to the coronary and systemic circulations. Implanted cells were characterized using histochemical staining for beta-galactosidase, immunofluorescent staining for muscle-specific antigens, and electron microscopy. Initially the injected cells were observed entrapped in myocardial capillaries. One week after injection myoblasts were present in the myocardial interstitium and were largely absent from the myocardial capillary bed. Implanted cells underwent myogenic development, characterized by the expression of a fast-twitch skeletal muscle sarcoendoplasmic reticulum calcium ATPase (SERCA1) and formation of myofilaments. Four months following injection myoblast-derived cells began to express a slow-twitch/cardiac protein, phospholamban, that is normally not expressed by C2C12 cells in vitro. Most surprisingly, regions of close apposition between LacZ labeled cells and native cardiomyocytes contained structures that resembled desmosomes, fascia adherens junctions, and gap junctions. The cardiac gap junction protein, connexin43, was localized to some of the interfaces between implanted cells and cardiomyocytes. Collectively, these findings suggest that arterially delivered myoblasts can be engrafted into the heart, and that prolonged residence in the myocardium may alter the phenotype of these skeletal muscle-derived cells. Further studies are necessary to determine whether arterial delivery of skeletal myoblasts can be developed as treatment for myocardial dysfunction.

Immunogenicity and smoking-cessation outcomes for a novel nicotine immunotherapeutic.

NicVAX, a nicotine vaccine (3'AmNic-rEPA), has been clinically evaluated to determine whether higher antibody (Ab) concentrations are associated with higher smoking abstinence rates and whether dosages and frequency of administration are associated with increased Ab response. This randomized, double-blinded, placebo-controlled multicenter clinical trial (N = 301 smokers) tested the results of 200- and 400-µg doses administered four or five times over a period of 6 months, as compared with placebo. 3'AmNic-rEPA recipients with the highest serum antinicotine Ab response (top 30% by area under the curve (AUC)) were significantly more likely than the placebo recipients (24.6% vs. 12.0%, P = 0.024, odds ratio (OR) = 2.69, 95% confidence interval (CI), 1.14-6.37) to attain 8 weeks of continuous abstinence from weeks 19 through 26. The five-injection, 400-µg dose regimen elicited the greatest Ab response and resulted in significantly higher abstinence rates than placebo. This study demonstrates, as proof of concept, that 3'AmNic-rEPA elicits Abs to nicotine and is associated with higher continuous abstinence rates (CAR). Its further development as a treatment for nicotine dependence is therefore justified.

Angiogenic gene therapy in patients with nonrevascularizable ischemic heart disease: a phase 2 randomized, controlled trial of AdVEGF(121) (AdVEGF121) versus maximum medical treatment.

The demonstration that angiogenic growth factors can stimulate new blood vessel growth and restore perfusion in animal models of myocardial ischemia has led to the development of strategies designed for the local production of angiogenic growth factors in patients who are not candidates for conventional revascularization. The results of recent clinical trials of proangiogenesis gene therapy have been disappointing; however, significant limitations in experimental design, in particular in gene transfer strategies, preclude drawing definitive conclusions. In the REVASC study cardiac gene transfer was optimized by direct intramyocardial delivery of a replication-deficient adenovirus-containing vascular endothelial growth factor (AdVEGF121, 4 x 10(10) particle units (p.u.)). Sixty-seven patients with severe angina due to coronary artery disease and no conventional options for revascularization were randomized to AdVEGF121 gene transfer via mini-thoracotomy or continuation of maximal medical treatment. Exercise time to 1 mm ST-segment depression, the predefined primary end-point analysis, was significantly increased in the AdVEGF121 group compared to control at 26 weeks (P=0.026), but not at 12 weeks. As well, total exercise duration and time to moderate angina at weeks 12 and 26, and in angina symptoms as measured by the Canadian Cardiovascular Society Angina Class and Seattle Angina Questionnaire were all improved by VEGF gene transfer (all P-values at 12 and 26 weeks < or =0.001). However, if anything the results of nuclear perfusion imaging favored the control group, although the AdVEGF121 group achieved higher workloads. Overall there was no significant difference in adverse events between the two groups, despite the fact that procedure-related events were seen only in the thoracotomy group. Therefore, administration of AdVEGF121 by direct intramyocardial injections resulted in objective improvement in exercise-induced ischemia in patients with refractory ischemic heart disease.

Hemodynamic effects of BTS 49465, a new long-acting systemic vasodilator drug, in patients with severe congestive heart failure.

The hemodynamic effects of BTS 49465, a new oral, direct-acting systemic vasodilator drug, were investigated in 10 patients with severe chronic congestive heart failure. One to 2 hours after the administration of 1.5 mg/kg orally, BTS 49465 produced significant increases in cardiac index, stroke volume index, and stroke work index (26%, 27%, and 23%, respectively, p less than 0.01 to 0.001) and marked decreases in left ventricular filling pressure (-12.6 mm Hg, 44%), mean pulmonary artery pressure (-13.2 mm Hg, 31%), and mean right atrial pressure (-7.7 mm Hg, 63%), all p less than 0.001, without significant changes in heart rate. These hemodynamic responses were accompanied by notable declines in systemic vascular resistance (-28%, p less than 0.001) and pulmonary arteriolar resistance (-24%, p less than 0.05). These effects persisted throughout the 24-hour period of observation. The decline in left ventricular filling pressure in our patients ranged in magnitude from 8 to 21 mm Hg, and varied linearly and directly with pretreatment values for left ventricular filling pressure (r = 0.69). The decrease in systemic vascular resistance ranged in magnitude from 3% to 40% and varied linearly and directly with pretreatment values for systemic vascular resistance (r = 0.85). These data indicate that BTS 49465, a new oral, direct-acting vasodilator agent, exerts balanced cardiocirculatory effects in patients with severe chronic heart failure, which may be sustained with once-daily oral administration.

The independency of choline transport and acetylcholine synthesis.

The coupling of choline transport to acetylcholine synthesis has been investigated by measurement of the isotopic dilution of a pulse of [3H]choline during its incorporation into the recently synthesised acetylcholine of cerebral cortex synaptosomes. Recently synthesised acetylcholine was identified as that containing 14C-labelled precursors introduced by a preincubation before the pulse. When [14C]glucose was used to label acetyl-CoA coupling ratios (calculated as the inverse of the dilution of extracellular [3H]choline during its incorporation into [3H]acetylcholine) of about 0.05-0.2 were found at a choline concentration of 1 microM, rising to 0.5 at choline concentrations of 10-50 microM. Experiments using [14C]choline as a precursor gave similar results, and it was shown that the isotopic dilution did not occur extrasynaptosomally and was not affected by low glucose concentrations. Coupling ratios were always less than unity and rose as the choline concentration increased. It is concluded that choline transported into the nerve terminal has no privileged access to choline acetyltransferase. The results can be explained by a rate-controlling transport of choline into the terminal followed by its rapid acetylation rather than any linkage or coupling of the two processes.

Myoblast cell grafting into heart muscle: cellular biology and potential applications.

This review surveys a wide range of cellular and molecular approaches to strengthening the injured or weakened heart, focusing on strategies to replace dysfunctional, necrotic, or apoptotic cardiomyocytes with new cells of mesodermal origin. A variety of cell types, including myogenic cell lines, adult skeletal myoblasts, immoratalized atrial cells, embryonic and adult cardiomyocytes, embryonic stem cells, tetratoma cells, genetically altered fibroblasts, smooth muscle cells, and bone marrow-derived cells have all been proposed as useful cells in cardiac repair and may have the capacity to perform cardiac work. We focus on the implantation of mesodermally derived cells, the best developed of the options. We review the developmental and cell biology that have stimulated these studies, examine the limitations of current knowledge, and identify challenges for the future, which we believe are considerable.

Adverse effects of converting-enzyme inhibition in patients with severe congestive heart failure: pathophysiology and management.

Although converting-enzyme inhibition is of established value in the management of patients with severe chronic congestive heart failure, troublesome adverse reactions occur frequently during the course of treatment and may cause physicians to interrupt effective therapy. The three most common adverse reactions that are seen in patients with heart failure following treatment with captopril and enalapril (symptomatic hypotension, functional renal insufficiency, hyperkalaemia) are predictable consequences of interfering with the homeostatic functions of the renin-angiotensin system, which evolved millions of years ago to preserve life in sodium-depleted states. It is not surprising, therefore, that these untoward effects can be prevented or reversed by increasing the dietary intake of salt or reducing the dose of concomitantly administered diuretics; their occurrence rarely requires discontinuation of drug therapy. Recognition of this link between sodium balance and the adverse effects of converting-enzyme inhibition is important, because most patients with severe heart failure who experience such untoward reactions can nevertheless be expected to improve clinically during long-term therapy, if effective treatment is not interrupted.

Preservation of glomerular filtration rate in human heart failure by activation of the renin-angiotensin system.

When renal perfusion pressure is reduced in experimentally induced low-output states, glomerular filtration rate is preserved by angiotensin II-mediated efferent arteriolar vasoconstriction, but available evidence in man suggests that angiotensin II supports renal function only to the extent that it preserves systemic blood pressure. We performed simultaneous assessments of cardiac and renal function in 56 patients with severe chronic heart failure before and after 1 to 3 months of converting-enzyme inhibition. Among the 29 patients with a pretreatment renal perfusion pressure under 70 mm Hg, patients with preserved renal function (creatinine clearance greater than 50 ml/min/1.73 m2) had markedly elevated values for plasma renin activity (11.8 +/- 3.8 ng/ml/hr) and showed a significant decline in creatinine clearance after converting-enzyme inhibition (61.1 +/- 3.0 to 45.9 +/- 5.3 ml/min/1.73 m2; p less than .05). In contrast, although similar with respect to all pretreatment demographic, hemodynamic, and clinical variables, patients with a creatinine clearance under 50 ml/min/1.73 m2 had low values for plasma renin activity (3.4 +/- 0.8 ng/ml/hr) and, despite similar drug-induced decreases in systemic blood pressure, showed no change in creatinine clearance after therapy with captopril or enalapril (32.6 +/- 2.5 to 41.4 +/- 3.8 ml/min/1.73 m2). Changes in creatinine clearance varied linearly and inversely with pretreatment values for plasma renin activity (r = - .64, p less than .001); converting-enzyme inhibition effectively abolished the pretreatment difference in renal function seen in the high- and low-renin subgroups. In the 27 patients with a renal perfusion pressure of 70 mm Hg or greater, creatinine clearance did not vary significantly with plasma renin activity and was not altered by therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Cumulative hemodynamic response to short-term treatment with flosequinan (BTS 49465), a new direct-acting vasodilator drug, in severe chronic congestive heart failure.

Pharmacologic tolerance develops rapidly to the hemodynamic effects of many vasodilator drugs used in the treatment of congestive heart failure. We evaluated the responses to 3 days of therapy with a new long-acting vasodilator drug, flosequinan (BTS 49465), in 16 patients with severe chronic heart failure. On each of the 3 days, flosequinan (100 or 150 mg orally) produced marked increases in cardiac index and decreases in left ventricular filling pressure, mean right atrial pressure, and systemic vascular resistance (all p less than 0.01) without significant changes in heart rate. Whereas the effects of flosequinan on right and left ventricular filling pressures on the first and third days were similar, cardiac index was higher and systemic vascular resistance was lower after the third dose than after the first dose of the drug, indicating the occurrence of a cumulative vasodilator effect on arterial resistance vessels. Since all hemodynamic changes persisted for longer than 24 h after each dose of the drug, the daily administration of flosequinan also produced a progressive improvement in the hemodynamic state recorded before each dose of the drug. These data indicate that pharmacologic tolerance does not develop to the effects of flosequinan during short-term therapy with the drug in patients with severe chronic heart failure. Instead, further hemodynamic improvement may occur because of a cumulative vasodilator effect that results from the drug's prolonged duration of action.

The alternative carboxyl termini of avian cardiac and brain sarcoplasmic reticulum/endoplasmic reticulum Ca(2+)-ATPases are on opposite sides of the membrane.

The sarcoplasmic/endoplasmic reticulum slow-twitch or cardiac Ca(2+)-ATPase (SERCA2) is expressed as two forms (SERCA2a and SERCA2b) which vary at their extreme carboxyl termini. SERCA2a and SERCA2b are derived from alternatively spliced primary transcripts of the same gene. These two alternative carboxyl termini are highly conserved in mammals (Eggermont, J. A., Wuytack, F., De Jaegere, S., Nelles, L., and Casteels, R. (1989) Biochem. J. 260, 757-761; Lytton, J., and MacLennan, D. H. (1988) J. Biol. Chem. 263, 15024-15031) and birds (Campbell, A. M., Kessler, P. D., Sagara, Y., Inesi, G., and Fambrough, D. M. (1991) J. Biol. Chem. 266, 16050-16055). The topology of SERCA2a is believed to be identical to the fast-twitch Ca(2+)-ATPase (SERCA1) with 10 membrane-spanning domains. Based on hydropathy analysis, the extended carboxyl terminus of SERCA2b is predicted to span the endoplasmic reticulum (ER) membrane an additional (i.e. 11th) time. We have added the human c-myc epitope, a 10-amino acid sequence recognized by monoclonal antibody 9E10, onto the carboxyl termini of SERCA2a and SERCA2b to test whether or not their carboxyl termini are on the same side of the ER membrane. The added epitopes do not appear to disrupt topology as judged from unaltered Ca2+ transport. Immunocytochemical studies demonstrate that SERCA2a and SERCA2b have their carboxyl termini on opposite sides of the ER membrane; SERCA2a's is in the cytosol and SERCA2b's is in the ER lumen.

Calcium-channel blockade in the management of severe chronic congestive heart failure: a bridge too far.

Because vasodilator therapy has become an established approach to the treatment of patients with severe chronic heart failure, there has been increasing interest in the use of the calcium channel-blocking drugs in the management of this disorder. This approach has particular appeal because approximately 60% of patients with heart failure have severe left ventricular dysfunction associated with coronary artery disease, and left ventricular systolic and diastolic performance in these patients may improve after interventions directed at improving myocardial blood flow. Unfortunately, all available calcium channel-blocking drugs possess potent negative inotropic effects; these are normally offset in patients without heart failure by activation of the sympathetic nervous system. Patients with severe left ventricular dysfunction, however, are exquisitely dependent on the transmembrane transport of calcium for maintenance of contractile function and show marked attenuation of adrenergic reflexes, which can no longer serve a homeostatic support function; hence, such patients are likely to experience notable cardiodepressant effects after calcium-channel blockade. In clinical trials, although some patients with severe chronic heart failure have been reported to benefit from short-term calcium-channel blockade, the hemodynamic benefits seen are modest compared with those from conventional vasodilator drugs, and little long-term improvement has been observed in randomized, double-blind trials. In addition, 10% to 40% of patients who receive short- and long-term therapy with verapamil, nifedipine, and diltiazem show evidence of serious hemodynamic or clinical deterioration.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequences of avian cardiac and brain SR/ER Ca(2+)-ATPases and functional comparisons with fast twitch Ca(2+)-ATPase. Calcium affinities and inhibitor effects.

Two similar forms of the cardiac/slow Ca(2+)-ATPase (SERCA2a and SERCA2b), differing in sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility, are expressed in chicken heart and brain (Kaprielian, Z., Campbell, A. M., and Fambrough, D. M. (1989) Mol. Brain Res. 6, 55-60). In the current study, cDNAs encoding each form were cloned and sequenced. Chicken SERCA2a is 94% identical to its rabbit homologue, while SERCA2b has an extended carboxyl terminus with 38 of 49 amino acids identical to mammalian homologues. SERCA2b mRNA contains the SERCA2a encoding sequence within its 3'-untranslated region. Chicken genomic DNA sequence reveals that the alternate RNA splicing used to produced SERCA2a and SERCA2b subtypes involves a splice site within an exon. Tissue culture cells expressing the avian SERCA2a, SERCA2b, and SERCA1, each targetting to the endoplasmic reticulum, were used to measure Ca2+ affinities and inhibitor effects; no differences among the three pumps were detected.

Movement of Ca(2+)-ATPase molecules within the sarcoplasmic/endoplasmic reticulum in skeletal muscle.

The endoplasmic reticulum undergoes rapid, microscopic changes in its structure, including extension and anastomosis of tubular elements. Such dynamism is expected to manifest itself also as rapid intermixing of membrane components, at least within subdomains of the endoplasmic reticulum. Here we present evidence of a similar dynamism in the sarcoplasmic reticulum of developing skeletal muscle. The sarcoplasmic reticulum is sometimes considered a specialized type of endoplasmic reticulum, but it appears to be a rather static set of membrane-bound elements, repetitively arranged to enwrap each sarcomere of each myofibril. Both endoplasmic reticulum and sarcoplasmic reticulum contain P-type Ca(2+)-ATPases that transport calcium from the cytosol into their lumen. In the experiments reported here, chicken and mouse cells were fused by polyethylene glycol, natural myogenic cell fusion, or Sendai virus. The redistribution of Ca(2+)-ATPase molecules between chick and mouse endoplasmic reticulum/sarcoplasmic reticulum was followed by immunofluorescence microscopy in which species-specific monoclonal antibodies to chick and mouse Ca(2+)-ATPases were used. Redistribution was time- and temperature-dependent but independent of protein synthesis as well as the method of cell fusion. Intermixing occurred on a time scale of tens of minutes at 37 degrees C. These results verify the dynamic nature of the sarcoplasmic reticulum and illustrate an aspect of the special relationship between endoplasmic reticulum and sarcoplasmic reticulum.

Can we expect vasodilator therapy to prolong life in patients with congestive heart failure?

Recent evidence from the Veterans Administration Vasodilator Heart Failure Trial supports the prophylactic use of a combination of hydralazine and isosorbide dinitrate to prolong life in patients with congestive heart failure. The clinical utility of such a combination vasodilator regimen may be limited, however, by its high frequency of adverse reactions, the lack of evidence that such a regimen enhances exercise tolerance, the inconvenience of taking a large number of tablets daily for a prophylactic indication, and the dearth of clinical experience combining hydralazine-nitrate with agents that may be clinically indicated to produce long-term symptomatic benefits (i.e., converting-enzyme inhibitors). Controlled evidence in animals and uncontrolled evidence in humans suggest that converting-enzyme inhibitors may also favorably modify prognosis, perhaps by antagonizing the deleterious actions of endogenous neurohormonal systems. Trials (presently in progress) are designed to evaluate the hypothesis that converting-enzyme inhibitors exert beneficial effects on the survival of patients with congestive heart failure comparable to those reported with hydralazine and isosorbide dinitrate.