Rotational atherectomy in CTO lesions: too risky? Outcome of rotational atherectomy in CTO lesions compared to non-CTO lesions.

AIMS: The aim of this study was to determine the feasibility of rotational atherectomy (RA) in chronic total occlusion (CTO) PCI and compare the success and complication rates of RA in CTO lesions versus non-occluded lesions. Data on RA in CTO are rare and it is unknown how procedural success and risk of RA in CTO lesions compare to RA in non-CTO lesions. METHODS AND RESULTS: RA was performed in 392 out of 17,919 PCI procedures (2.2% of the PCI cohort) and classified as RA CTO (n=75) and RA non-CTO (n=317). Procedural success and MACCE in both groups were assessed by two investigators. All RA procedures were analysed for dissections prior to RA, which were defined according to the NHLBI classification. Baseline characteristics were not significantly different in the two groups but, in RA CTO, lesion type was more complex (p<0.001), stented segments were longer (35.0±22.7 vs. 46.0±24.8 mm, p<0.001) and mean burr size was smaller (1.61±0.17 vs. 1.49±0.18 mm, p<0.001). Procedural success and complications were not different (RA non-CTO 96.2% and RA CTO 94.7%, RA non-CTO 2.5% and RA CTO 4.0%, respectively). RA performed in dissection planes had a 100% procedure success rate in CTO and a 92% success rate in non-CTO. CONCLUSIONS: RA in CTO is as safe and as effective as RA in non-CTO. The presence of dissections prior to RA in CTO lesions as well as in non-CTO lesions does not seem to have a negative impact on outcome.

Long-term major adverse cardiac and cerebrovascular events (MACCE) rate : Comparison of retrograde and antegrade recanalization of chronic total coronary occlusions.

BACKGROUND: The recanalization success rate of chronic total occlusion (CTO) percutaneous coronary interventions (PCI) can be increased by the retrograde approach; however, the long-term outcome of patients undergoing retrograde procedures is unknown. AIM: We aimed to evaluate the long-term major adverse cardiac and cerebrovascular event (MACCE) rate (e.g. death, myocardial infarction, coronary artery bypass surgery and stroke) in patients after retrograde versus antegrade CTO-PCI. METHODS AND RESULTS: In a prospective single center study from January 2008 to June 2012, 396 consecutive patients with CTO (≥3 months old) were enrolled. The mean age was 63.4 ± 10.3 years and 86.4% were male. The success rate of the total patient cohort was 88.6%. The retrograde PCI, only attempted after a failed antegrade intervention, was performed in 18% (n = 71) of patients. Long-term MACCE rate (mean follow up 2.3 ± 1.6 years) was significantly higher in the unsuccessful compared to the successful CTO-PCI group (23.1% versus 9.4%, p = 0.01) and this was also the case in the subgroup of antegrade CTO-PCI. In the retrograde subgroup, however, procedural success had no impact on outcome. Patients with unsuccessful retrograde CTO-PCI had a significantly better collateral connection compared to patients with an unsuccessful antegrade approach. Independent predictors for MACCE were peripheral artery disease and an ejection fraction ≤30%. CONCLUSION: The long-term MACCE rate after unsuccessful recanalization was significantly higher, which was driven by a higher MACCE rate after unsuccessful versus successful antegrade approaches. In contrast, procedural success in the retrograde group had no impact on outcome.

Impact of cardiac comorbidities on early and 1-year outcome after percutaneous mitral valve interventions: data from the German transcatheter mitral valve interventions (TRAMI) registry.

AIMS: The use of the MitraClip system has gained widespread acceptance for the treatment of patients with mitral regurgitation (MR) who are not suitable for the conventional surgery. This study sought to investigate the early and 1-year outcome after MitraClip therapy of patients with MR and cardiac comorbidities. METHODS AND RESULTS: Outcomes through 12-month follow-up of patients (n = 528) who underwent MitraClip implantation were obtained from the German transcatheter mitral valve interventions (TRAMI) registry. The majority of these patients (n = 409, 77.5 %) also suffered from coronary artery disease (CAD). Patients with a dilated cardiomyopathy (DCM, n = 65, 12.3 %) or concomitant valvular aortic disease (AV, n = 54, 10.2 %) were less frequent. Although the prevalent pathogenesis was functional MR, patients with DCM had significantly more frequent a functional MR (96.9 %) compared to patients with CAD (74.9 %) or AV (62.5 %, p < 0.001). Technical success was achieved in 97.5 % of patients. Procedural echocardiograms demonstrated in the vast majority of patients a reduction from severe MR III to mild MR I with no difference between the groups (p = 0.83). The peri-procedural complication rate was very low. At 30-day and 12-month follow-up, the majority of patients were in NYHA functional class II or lower. The rate of death, stroke, and myocardial infarction (MACCE) was comparable in the three patient groups during 12-month follow-up (DCM 26.9 %, CAD 30.3 % and AV 27.5 %, p = 0.85). CONCLUSIONS: The MitraClip implantation is feasible and safe even in high-risk patients with MR and cardiac comorbidities.

Recanalization of chronic total coronary occlusions--high success rate despite a restrictive use of the retrograde approach.

AIM: The retrograde approach in chronic total occlusion (CTO) percutaneous coronary intervention (PCI) is increasingly being used as a first-line intervention despite a higher radiation exposure, contrast volume, and a higher major adverse cardiac event (MACE) rate compared with the antegrade approach. It was aimed to evaluate the overall success rate of CTO-PCI over time when the retrograde approach was restrictively used only after a failed antegrade attempt. METHODS AND RESULTS: In a prospective single operator registry from January 2008 to December 2012 about 436 consecutive patients underwent a CTO-PCI. Mean age was 63.4 ± 10.3 years, and 86% were male. The overall success rate improved significantly over time [68% (first quartile) to 91% (fourth quartile), P < 0.001] due to a significant increase of the antegrade success rate. This could be achieved by a retrograde approach of less than 20% with no change over time. The overall in-hospital MACE rate was 0.69% with no difference between antegrade and retrograde procedures. CONCLUSIONS: A high CTO-PCI success rate of above 90% could be achieved with a restrictive use of the retrograde technique.

Beyond the early stages: insights from the ASSURE registry on bioresorbable vascular scaffolds.

AIMS: Bioresorbable vascular scaffolds (BVS) have been available on the European market since November 2011. The ASSURE registry aims to investigate the safety and efficacy of the Absorb everolimus-eluting bioresorbable vascular scaffold in a real-world setting. METHODS AND RESULTS: Patients with de novo coronary artery disease were consecutively enrolled at six German centres in this prospective registry. Outcomes were procedural success, cardiovascular death, myocardial infarction, and ischaemia-driven target lesion revascularisation (TLR). Angiographic parameters were assessed quantitatively and visual estimates of lesion dimensions were studied. One hundred and eighty-three patients were treated. In 128 (64.7%) lesions a complex ACC/AHA morphology was present. Procedural success was achieved in all patients. Acute gain was 1.54±0.51 mm, resulting in a final minimal lumen diameter (MLD), which met the baseline reference vessel diameter (RVD), although visual estimates overrated the RVD by 0.5±0.5 mm. Up to 12 months, one patient (0.5%) had died from gastrointestinal bleeding, three (1.7%) non-target vessel myocardial infarctions occurred, and five (2.8%) TLR had become necessary because of restenosis. CONCLUSIONS: One-year results suggest that bioresorbable vascular scaffolds for de novo coronary artery disease are associated with favourable clinical and functional outcomes in routine clinical practice despite a visually overestimated RVD.

Physicians' radiation exposure in the catheterization lab: does the type of procedure matter?

OBJECTIVES: This study sought to evaluate differences in radiation exposure of the operator depending on the type of catheterization lab procedure. BACKGROUND: Invasive cardiologists and angiologists are exposed to long-term, low-dose occupational radiation. Increased workload and specialization require more detailed knowledge of the extent and cause of the radiation exposure. METHODS: In this prospective single-center experience, radiation doses of 3 operators were measured by real-time dosimetry for body, neck, and hand during 284 procedures in 281 patients over a period of 14 weeks. To determine the association between the type of procedure and the doses and to draw a pairwise comparison between the procedures, 3 mixed models were used. RESULTS: The type of procedure, the patient's body mass index, and the fluoroscopy time were independently associated with the operator's radiation exposure. Per procedure, the operators were exposed to a mean effective dose (E) of 2.2 ± 5.9 µSv. Compared with coronary angiography, E was 2.3-fold higher in pelvic procedures (95% confidence interval [CI]: 1.7 to 3.0, p < 0.001), 1.7-fold higher in upper limb procedures (95% CI: 1.3 to 2.1, p < 0.001), and 1.4-fold higher in below-the-knee procedures (95% CI: 1.1 to 2.0, p = 0.023). The mean eye dose was 19.1 ± 37.6 µSv. Eye doses were significantly higher in peripheral procedures than in coronary angiography procedures. The mean hand dose was 99.6 ± 196.0 µSv. Hand doses were significantly higher in pelvic than in coronary angiography, upper limb, and below-the-knee procedures. CONCLUSIONS: Endovascular procedures for pelvic, upper limb, and below-the-knee disease are accompanied with a higher radiation exposure of the operator than with coronary procedures.

Endovascular repair of ascending aortic aneurysm by transapical approach and periscope technique.

PURPOSE: To demonstrate transapical stent-graft implantation for the treatment of an ascending aortic aneurysm simultaneously using the "periscope" technique for all supra-aortic branches. TECHNIQUE: The treatment plan is demonstrated in a 67-year-old man with prior ascending aortic replacement and known ascending aortic aneurysm who presented with acute severe chest pain. Computed tomographic angiography (CTA) revealed an 11-cm ruptured aneurysm of the ascending aorta distal to the prosthesis. Surgery was impossible due to direct contact of the aneurysm with the sternum. Conventional retrograde stent-graft implantation was infeasible because of a sharp kink of the descending thoracic aorta, so the stent-grafts were implanted via a transapical approach. To provide blood flow to the supra-aortic branches, periscope grafts oriented from the target vessels down the descending thoracic aorta were implanted in all branches before main stent-graft placement. Completion angiography and subsequent CTA documented satisfactory retrograde perfusion of the supra-aortic branches via the periscope grafts. CONCLUSION: A dual approach in terms of transapical stent-graft implantation and the periscope technique for perfusion of the supra-aortic branches may be an option for the treatment of inoperable aneurysms of the ascending aorta.

Endovascular reconstruction of the aortic bifurcation in patients with Leriche syndrome.

BACKGROUND: The Leriche syndrome with contiguous total occlusions of the infrarenal aorta and the iliac arteries is a variant of Trans-Atlantic Inter-Society Consensus (TASC) type D aortoiliac disease, for which surgery is the recommended treatment of choice. We sought to prospectively assess the feasibility and safety of an endovascular therapeutic approach. METHODS: Eleven consecutive patients with Leriche syndrome (eight men; 64 +/- 12 years) constituted the study cohort. The treatment strategy consisted of recanalization by transbrachial access of the occluded segments and subsequent transfemoral angioplasty with selective stent placement in the distal aorta and primary nitinol stent placement in the iliac arteries. RESULTS: Bilateral endovascular success was achieved in eight patients (73%), unilateral success in the other three patients. Seven patients received aortic stents; the total stented segment length in 19 iliac arteries successfully recanalized amounted to a median of 18 cm (range 12-26 cm). There was one periprocedural complication, an acute thrombotic aortoiliac occlusion managed by thrombolysis. One patient with unilateral endovascular success had to undergo femorofemoral crossover bypass grafting. At a median of 14 months, significant hemodynamic improvement was observed in successfully revascularized legs (ankle-brachial index, 0.79 +/- 0.20 vs. 0.48 +/- 0.08 at baseline; P = 0.0004); walking capacity as well as Rutherford category of peripheral arterial disease had improved in all patients. CONCLUSIONS: In this small series of patients with Leriche syndrome, the reconstruction of the totally occluded aortoiliac bifurcation by endoluminal means was shown to be feasible and safe and associated with excellent mid-term clinical outcomes.

The calcium channel blocker felodipine attenuates the positive hemodynamic effects of the beta-blocker metoprolol in severe dilated cardiomyopathy--a prospective, randomized, double-blind and placebo-controlled study with invasive hemodynamic assessment.

BACKGROUND: In addition to standard therapy with ACE-inhibitors, digitalis and diuretics, beta-adrenergic receptor blockers have become a widely accepted strategy in the treatment of chronic heart failure. The role of calcium antagonists in CHF however remains controversial. To evaluate if a combination therapy of metoprolol and felodipine might improve hemodynamic parameters, a randomized and placebo-controlled study was designed. METHODS AND RESULTS: Sixty-three patients with DCMP, LVEF 3 months in NYHA II-III on standard medication were prospectively treated with either a) a combination of metoprolol+felodipine (MF group, n=20), b) metoprolol+felodipine-placebo (MP group, n=23), or c) metoprolol-placebo+felodipine-placebo (PP group, n=20). Compared to baseline, LVEF and LVEDD significantly improved after 6 months in the MP group (LVEF: 36+/-2% vs 29+/-2%, p<0.01; LVEDD: 68+/-3 mm vs 64+/-3 mm, p<0.05), whereas in the other treatment groups only minor changes were observed. A significant benefit in hemodynamic parameters as determined by right heart catheterization was noted also only in the MP group with a marked reduction in PAP mean (17 vs 24 mmHg, p<0.01), PCWP (10 vs 15 mmHg, p<0.001) resulting in a significant increase in cardiac and stroke volume index at rest with no marked changes in the MF and PP group. CONCLUSION: beta-blocker treatment in CHF patients improves left ventricular function and additionally invasive hemodynamic measurements both at rest and during exercise. In contrast, the combined therapy with the long-acting calcium antagonist felodipine neutralizes these beneficial effects of metoprolol therapy to almost placebo level, providing evidence based on hemodynamic measurements that this combination should be avoided in patients with CHF.

The adverse cardiopulmonary phenotype of caveolin-1 deficient mice is mediated by a dysfunctional endothelium.

Recently generated caveolin-1 deficient mice (cav-1(-/-)) display several physiological alterations such as severe heart failure and lung fibrosis. The molecular mechanisms how the loss of caveolin-1 (cav-1) mediates these alterations are currently under debate. A plethora of studies support a role of cav-1 as a negative regulator of endothelial nitric oxide synthase (eNOS). Accordingly, constitutive eNOS hyperactivation was observed in cav-1(-/-). Given the hyperactivated eNOS enzyme we hypothesized that disturbed eNOS function is involved in the development of the cardiopulmonary pathologies in cav-1(-/-). The present study argues that loss of cav-1 results in enhanced eNOS activity but not in increased vascular tetrahydrobiopterin (BH(4)) levels (which acts as an essential eNOS cofactor) thereby causing a stoichiometric discordance between eNOS activity and BH(4) sufficient to cause dysfunctional eNOS signaling. The resultant oxidative stress is largely responsible for major cardiac and pulmonary defects observed in cav-1(-/-). BH(4) donation to cav-1(-/-) led to a normalized BH(4)/BH(2) ratio, to reduced oxidant stress, to substantial improvements of both systolic and diastolic heart function and to marked amelioration of the impaired lung phenotype. Notably, the antioxidant tetrahydroneopterin which is not essential for eNOS function showed no relevant effect. Taken together these novel findings indicate that dysfunctional eNOS is of central importance in the genesis of the cardiopulmonary phenotype of cav-1(-/-). Additionally, these findings are generally of paramount importance since they underline the deleterious role of an uncoupled eNOS in cardiovascular pathology and they additionally suggest BH(4) as an effective cure.

Chronic NOS inhibition prevents adverse lung remodeling and pulmonary arterial hypertension in caveolin-1 knockout mice.

Recently generated caveolin-1 deficient mice (cav-1 ko) suffer from severe lung fibrosis with marked pulmonary hypertension and arterial hypoxemia and may therefore serve as an useful animal model of this devastating human disorder. Accumulating evidence strongly supports the negative regulatory influence of caveolin-1 on endothelial nitric oxide synthase resulting in a constitutive hyperactivation of the nitric oxide (NO) pathway in cav-1 ko. We therefore hypothesized that a disturbed NO signaling is implicated in the evolution of the adverse lung phenotype of cav-1 ko. For this purpose, cav-1 ko of 2 months age were compared with knockout counterparts experiencing 2-month postnatal NO synthase inhibition by NG-nitro-l-arginine methyl ester (L-NAME) treatment. Chronic l-NAME administration prevented adverse lung remodeling in cav-1 ko. Furthermore, l-NAME donation led to a normalized oxygen saturation (91.5+/-1.8% vs. 98.5+/-2.3%, P<0.01, n=10-12), a marked decrease in right ventricular hypertrophy (LV/RV ratio: 4.0+/-0.3 vs. 2.7+/-0.3, P<0.01, n=10-12) and reductions of the elevated pulmonary artery pressure (40.2+/-3.1 mmHg vs. 26.3+/-4.6 mmHg, P<0.01, n=6). Collectively, these improvements resulted in an enhanced exercise capacity of l-NAME-treated cav-1 ko. Finally, we found evidence for enhanced oxidative stress in untreated cav-1 ko which was substantially reduced by chronic l-NAME administration to cav-1 ko. In view of these data, we speculate that a perturbation of NO signaling, together with enhanced O2(-) production originating from NO synthases, may play a pivotal role in the pathogenesis of the adverse pulmonary phenotype seen in cav-1 ko.

Caveolae and caveolin in transmembrane signaling: Implications for human disease.

The identification of various signaling molecules found within caveolae and their functional interaction with the integral membrane protein caveolin, a major structural component of caveolae, suggests that these membrane microdomains participate in transmembrane signaling. Several lines of evidence indicate that caveolin may act as a scaffolding protein by direct interaction with and modulation of the activity of multiple signaling molecules. The compartmentation of various signaling molecules in caveolae and their direct and functional interaction with caveolin provides a paradigm by which these membrane microdomains are involved in regulating signal transduction pathways. By dysregulation of these signal transduction pathways caveolins may be involved in the pathogenesis of various diseases. This review focuses on the implications as well as controversies of the contribution of caveolae and caveolins for several human diseases and the potential implications to therapeutic strategies.

Disruption of caveolin-1 leads to enhanced nitrosative stress and severe systolic and diastolic heart failure.

Although caveolin-1 is not expressed in cardiomyocytes, this protein is assumed to act as a key regulator in the development of cardiomyopathy. In view of recent discordant findings we aimed to elucidate the cardiac phenotype of independently generated caveolin-1 knockout mice (cav-1(-/-)) and to unveil causative mechanisms. Invasive hemodynamic measurements of cav-1(-/-) show a severely reduced systolic and diastolic heart function. Additionally, genetic ablation of caveolin-1 leads to a striking biventricular hypertrophy and to a sustained eNOS-hyperactivation yielding increased systemic NO levels. Furthermore, a diminished ATP content and reduced levels of cyclic AMP in hearts of knockout animals were measured. Taken together, these results indicate that genetic disruption of caveolin-1 is sufficient to induce a severe biventricular hypertrophy with signs of systolic and diastolic heart failure. Collectively, our findings suggest a causative role of a sustained nitrosative stress in the development of the pronounced cardiac impairment.

Decreased caveolin-1 in atheroma: loss of antiproliferative control of vascular smooth muscle cells in atherosclerosis.

OBJECTIVE: Proliferation of vascular smooth muscle cells (VSMC) is involved in the pathogenesis of primary atherosclerosis and restenosis after angioplasty. On the background of the antiproliferative activities of caveolin-1, the present study focused on the expression of caveolin-1 in proliferating VSMC of human atheroma. METHODS: VSMC were isolated from wild-type (Wt) and caveolin-1 knockout mice (Cav-/-). Proliferation of Wt-VSMC after supplementation of serum or Cav-/-VSMC after adenoviral overexpression of caveolin-1 was documented by either Western blot analysis of the cyclin-dependent kinase (Cdk) inhibitor p27kip1 and the proliferating cell nuclear antigen (PCNA) or BrdU incorporation. Using immunohistochemistry the proliferation of VSMC derived from atheroma of human carotid vessels as well as the expression of caveolin-1 in these cells were investigated ex vivo. RESULTS: Supplementation of serum to Wt-VSMC resulted in an augmented cell cycle entry and a concomitant decrease of caveolin-1 expression. Inversely, adenoviral overexpression of caveolin-1 in Cav-/-VSMC inhibited cellular proliferation. Corresponding to these in vitro data, the expression of caveolin-1 was significantly decreased in proliferating VSMC of human atheroma. CONCLUSION: The proliferation of VSMC in vitro and in human atheroma is associated with a decrease of caveolin-1 expression. These data suggest that the loss of antiproliferative control by caveolin-1 plays a pivotal role in VSMC proliferation in atherosclerosis.

Caveolin-1 facilitates mechanosensitive protein kinase B (Akt) signaling in vitro and in vivo.

Mechanotransduction represents an integral part of vascular homeostasis and contributes to vascular lesion formation. Previously, we demonstrated a mechanosensitive activation of phosphoinositide 3-kinase (PI3-K)/protein kinase B (Akt) resulting in p27Kip1 transcriptional downregulation and cell cycle entry of vascular smooth muscle cells (VSMC). In this study, we further elucidated the signaling from outside-in toward PI3-K/Akt in vitro and in an in vivo model of elevated tensile force. When VSMC were subjected to cyclic stretch (0.5 Hz at 125% resting length), PI3-K, Akt, and Src kinases were found activated. Disrupting caveolar structures with beta-cyclodextrin or transfection of VSMC with caveolin-1 antisense oligonucleotides (ODN) prevented PI3-K and Akt activation and cell cycle entry. Furthermore, PI3-K and Akt were resistant to activation when Src kinases were inhibited pharmacologically or by overexpression of a kinase-dead c-Src mutant. alpha(V)beta3 integrins were identified to colocalize with PI3-K/caveolin-1 complexes, and blockade of alpha(V)beta3 integrins prevented Akt activation. The central role of caveolin-1 in mechanotransduction was further examined in an in vivo model of elevated tensile force. Interposition of wild-type (WT) jugular veins into WT carotid arteries resulted in a rapid Akt activation within the veins that was almost abolished when veins of caveolin-1 knockout (KO) mice were used. Furthermore, late neointima formation within the KO veins was significantly reduced. Our study provides evidence that PI3-K/Akt is critically involved in mechanotransduction of VSMC in vitro and within the vasculature in vivo. Furthermore, caveolin-1 is essential for the integrin-mediated activation of PI3-K/Akt.

Transregulation of the alpha2-adrenergic signal transduction pathway by chronic beta-blockade: a novel mechanism for decreased platelet aggregation in patients.

Platelets play a pivotal role in the pathophysiology of acute coronary syndromes. Chronic beta-blockade has been shown to improve the long-term clinical outcome in coronary heart disease. Because platelets play a central role in thrombus formation, the aim of the present study was to investigate if chronic beta-blockade may transregulate the expression of alpha2-adrenergic receptors on human platelets and via this mechanism may modulate platelet activation. The densities of alpha2-adrenergic receptors of platelets were determined in healthy volunteers under chronic beta-blockade and as alpha2-adrenergic receptor-mediated function in catecholamine-induced platelet aggregation was determined. Chronic beta-blockade induced a time-dependent reduction of alpha2-adrenergic receptors. This reduction was accompanied by a decrease of the alpha-subunit of Gi proteins as demonstrated by Western blot analysis. This transregulation at both the receptor level and the G-protein level resulted in an almost complete loss of the alpha2-adrenergic receptor-mediated inhibition of adenylyl cyclase. The impairment of the alpha2-adrenergic receptor system correlated with a reduction of the catecholamine-induced activation and aggregation of human platelets. The functional transregulation of alpha2-adrenergic receptors by chronic beta-blockade in platelets and the consequent impairment of platelet activation may contribute to the therapeutic success of beta-blocker therapy.

Ischemic preconditioning prevents ischemia-induced beta-adrenergic receptor sequestration.

Preconditioning enables endogenous protection to repeated myocardial ischemia. However, the effect of preconditioning on beta1 adrenergic receptor (AR) signal remains controversial. We have recently developed receptor assay system using whole cells, in which overexpressed cell surface beta ARs can be readily quantitated without disrupting the cell. Using this technique, we examined the effects of chemical/metabolic ischemia on the beta1 AR sequestration and adenylyl cyclase activity. Isoproterenol treatment, but not forskolin treatment, of HEK293T cells overexpressing beta1 ARs led to a rapid decrease (within 2 hours) in the number of the cell surface receptor, which was negated in the presence of concanavalin A. Similarly, treatment of cells with potassium cyanide and 2-deoxy-D-glucose (chemical/metabolic ischemia) induced similar receptor sequestration. When isoproterenol was superimposed on chemical/metabolic ischemia, the degree of sequestration became greater. However, when cells were pre-exposed to potassium cyanide on the preceding day (chemical preconditioning), the sequestration induced by either isoproterenol or chemical/metabolic ischemia was attenuated. Adenylyl cyclase catalytic activity as assessed by stimulation with forskolin was decreased by chemical/metabolic ischemia but fully recovered after 24 hours, suggesting that chemical/metabolic ischemia treatment did not alter cell viability. Putting together, chemical/metabolic ischemia induced beta1 AR sequestration in a similar manner to isoproterenol. In addition, preconditioning prevented the beta1 AR sequestration induced by both isoproterenol and chemical/metabolic ischemia. Pre-conditioning may play a role in preserving the cell surface beta ARs by inhibiting the sequestration that is usually induced by an ischemic event or beta adrenergic stimulation.

Characterization of beta-adrenergic receptor sequestration by newly developed whole cell binding assays.

Upon agonist binding, beta-adrenergic receptors sequestrate from the cell surface plasma membrane to cytosol. In the present study, we examine the kinetics of sequestration of beta1-adrenergic receptor and beta3-adrenergic receptor subtypes by radioligand binding assays using whole cells ('whole cell binding assays'). We found that HEK293T cells, but not COS1 cells, were readily and uniformly detached from the culture dish upon exposure to ice-cold phosphate-buffered saline. Using this property of HEK293T cells, we conducted whole cell binding assays using a hydrophilic antagonist ([3H]CGP-12177) and HEK293T cells transiently overexpressing human beta1-adrenergic receptor or beta3-adrenergic receptor. The Bmax and Kd values were 5.96 +/- 0.97 pmol/mg protein and 1 +/- 0.23 nM for the beta1-adrenergic receptor, and were 1.84 +/- 0.13 pmol/mg protein and 44.7 +/- 2.5 nM for the beta3-adrenergic receptor, respectively. Isoproterenol treatment, but not 6-[3-(dimethylamino)propionyl]forskolin treatment, for 2 h resulted in a dose-dependent loss of the number of the cell surface beta1-adrenergic receptor. At 100 microM, 36.6 +/- 5.7% of the cell surface beta1-adrenergic receptor was lost. In contrast, the cell surface beta3-adrenergic receptor number remained unchanged with isoproterenol treatment. Thus, beta1-adrenergic receptor sequestrates upon agonist stimulation but the same agonist stimulation does not induce beta3-adrenergic receptor sequestration, as demonstrated by our whole cell binding assays.