The clinical impact of dynamic intraventricular obstruction during dobutamine stress echocardiography.

We selected 73 consecutive patients without myocardial-infarction, hypertrophic cardiomyopathy or hypertension complaining of effort chest discomfort/dyspnoea, and/or reporting exercise ischaemic ECG changes, and submitted them to simultaneous dobutamine stress echocardiography (DSE) and 99mTc tetrofosmin SPECT (T SPECT) and to coronary angiography to evaluate the clinical impact of intraventricular obstruction (IVO) during dobutamine infusion. Sixteen patients (22%, 7 males, mean age+/-SD 63+/-8 years, group 1) developed IVO (mean CW Doppler velocity+/-SD: 3.8+/-1.0 m/s) and 57 (41 males, mean age+/-SD 63+/-10 years, group 2) did not. The two groups had similar incidence of angina and ischaemic ECG changes at exercise tolerance test. DSE did not demonstrate wall motion abnormalities in any group 1 patient while T SPECT showed a perfusion defect in the only one with coronary artery disease (CAD). DSE reproduced symptoms in a higher percentage of patients with than without IVO, while there was no statistical difference in the reproduction of ischaemic ECG changes, despite CAD prevalence was much lower in group 1. Group 1 patients remained asymptomatic on beta-blockers at 12-month follow-up. Dobutamine-induced IVO, by reproducing symptoms, suggests that IVO plays a role in the clinical setting in patients without CAD complaining of unexplained reduced effort tolerance who should undergo DSE.

Echocardiographic diagnosis of coronary sinus type atrial septal defect. A case report.

BACKGROUND: Coronary sinus type atrial defect is the result of an incomplete formation of the atriovenous fold. This is a rare anomaly that in a very few cases took advantage of echocardiographic diagnosis before surgery. We report on a case of coronary sinus type atrial septal defect diagnosed by means of transthoracic and transesophageal echocardiography. PATIENT: A 65 year old woman who was admitted to hospital for evaluation of dyspnea and pre-syncope. A diagnosis of secundum type atrial septal defect had been achieved few months before. METHOD DESCRIPTION: Color Doppler transthoracic echocardiography demonstrated evidence of left-to-right shunt through the coronary sinus-left atrium common wall, while transesophageal echocardiography showed a defect in the coronary sinus roof in its terminal portion, proximal to the atrial septum. At that level the shunt flow was demonstrated by the presence of a negative contrast after contrast injection. Both transthoracic and transesophageal contrast echocardiographies demonstrated the persistence of a left superior vena cava draining into the enlarged coronary sinus: the existence of a right-to-left shunt at the coronary sinus level suggested by transthoracic echocardiographic examination was not confirmed by transesophageal echocardiography. CONCLUSIONS: This is one of the few reported cases of coronary sinus type atrial defect diagnosed noninvasively and the diagnostic usefulness of both transthoracic and transesophageal echocardiographic approaches is stressed.

Left-ventricular diastolic dysfunction during pneumonectomy--a transesophageal echocardiographic study.

Left-ventricular dysfunction, with acute increase in capillary pulmonary pressure, can unexpectedly develop in patients submitted to pneumonectomy. In order to study the morphofunctional modifications induced by pneumonectomy on the left cardiac chambers, we performed intraoperative transesophageal echocardiography (TEE) in 8 patients (7 males, mean age 66 years) undergoing pneumonectomy for lung cancer. No patient had any cardiac involvement before surgery. The opening of the pericardium was associated with a slight paradoxical movement of the basal interventricular septum. After ligature of the pulmonary artery, the interventricular septum changed its geometry, losing the normal curvature and becoming rectilinear. These changes were related to an increase in right-ventricular (RV) dimensions. In all patients the pulmonary vein flow-profile (pulsed Doppler) showed an increased turbulence, associated with a reduced amplitude (5 patients) or an inversion (3 patients) of the second systolic component and with the development of mild mitral regurgitation (color Doppler). These changes disappeared at the end of intervention, before chest closure. No alteration in left-ventricular systolic function was found. These results suggest that the altered geometry of the interventricular septum, mainly due to acute RV overload, induces a transient left-ventricular diastolic dysfunction, associated with mild mitral regurgitation.

Integrin-mediated neurite outgrowth in neuroblastoma cells depends on the activation of potassium channels.

Electrical signals elicited by integrin interaction with ECM components and their role in neurite outgrowth were studied in two clones (N1 and N7) isolated from 41A3 murine neuroblastoma cell line. Although the two clones similarly adhered to fibronectin (FN) and vitronectin (VN), this adhesion induced neurite outgrowth in N1 but not in N7 cells. Patch clamp recordings in whole cell configuration showed that, upon adhesion to FN or VN but not to platelet factor 4 (PF4), N1 cells undergo a marked (approximately equal to 20 mV) hyperpolarization of the resting potential (Vrest) that occurred within the first 20 min after cell contact with ECM, and persisted for approximately 1 h before reverting to the time zero values. This hyperpolarization was totally absent in N7 cells. A detailed analysis of the molecular mechanisms involved in N1 and N7 cell adhesion to ECM substrata was performed by using antibodies raised against the FN receptor and synthetic peptides variously competing with the FN or VN binding to integrin receptor (GRGDSP and GRGESP). Antibodies, as well as GRGDSP, abolished adhesion of N1 and N7 clones to FN and VN, revealing a similar implication of integrins in the adhesion of these clones to the ECM proteins. However, these anti-adhesive treatments, while ineffective on Vrest of N7 cells, abolished in N1 cells the FN- or VN-induced hyperpolarization and neurite outgrowth, that appeared therefore strictly associated and integrin-mediated phenomena. The nature of this association was deepened through a comparative analysis of the integrin profiles and the ion channels of N1 and N7 cells. The integrin immunoprecipitation profile resulted very similarly in the two clones, with only minor differences concerning the alpha V containing complexes. Both clones possessed Ca2+ and K+ delayed rectifier (KDR) channels, while only N1 cells were endowed with inward rectifier K+ (KIR) channels. The latter governed the Vrest, and, unlike KDR channels, were blocked by Ba2+ and Cs+. By moving patched cells in contact with FN-coated beads, it was shown that KIR channel activation was responsible for the FN-mediated hyperpolarization of Vrest. Treatment with Pertuxis toxin (PTX) abolished this hyperpolarization and neurite outgrowth, indicating that a G protein is interposed between integrins and KIR channels and that the activation of these channels is required for neuritogenesis. In fact, the block of KIR channels by Cs+ abolished both hyperpolarization and neurite outgrowth, provided that the cation was supplied during the first two hours after N1 cell contact with FN.(ABSTRACT TRUNCATED AT 400 WORDS)

Polar/apolar compounds induce leukemia cell differentiation by modulating cell-surface potential.

The mechanism of action of polar/apolar inducers of cell differentiation, such as dimethyl sulfoxide and hexamethylene-bisacetamide, is still obscure. In this paper evidence is provided that their effects on murine erythroleukemia cells are modulated by various extracellular cations as a precise function of the cation effects on membrane surface potential. The interfacial effects of the inducers were directly measured on the charged electrode, showing that both dimethyl sulfoxide and hexamethylene-bisacetamide, at the effective concentrations for cell differentiation and within the physiological range of charge density, adsorb at the charged surface and produce a potential shift. A linear correlation was found between this shift and the inducer effects on cell differentiation. Besides offering a different interpretation of the mechanism of action of the inducers, these findings indicate that surface potential has a signaling function. They may also be relevant to cancer treatments based on tumor-cell commitment to terminal differentiation.

Intra and extracellular surface charges near Ca2+ channels in neurons and neuroblastoma cells.

The properties of low (LVA) and high (HVA) voltage-activated calcium currents were investigated in rat sensory neurons and a murine neuroblastoma cell line exposed to various concentrations of intra- or extracellular monovalent ([c+]i/o) and trivalent ([c3+]i/o) cations. In neurons, when [c+]i was changed from 150 to 20 mM, positive shifts of 18-28 mV were observed in activation curves of both LVA and HVA currents, as well as in LVA inactivation curves. Extracellularly, in divalent-free solutions, [c+]o of 20-50 mM produced medium (12-22 mV) negative shifts of the LVA channel properties. These data were used to estimate, by a "screening" model, a negative surface charge density around neuron's calcium channels of 1/1,000 and 1/1,325 eA-2 at the outside or inside face, respectively. In the presence of physiological concentrations of divalent cations, [c+]o of 20-60 mM caused smaller (4-11 mV) negative shifts of the activation and inactivation curves, which can be explained by assuming a partial neutralization of negative charges by divalent cations. By applying the above procedure to LVA channels of neuroblastoma cells, the ratio of extra- to intracellular surface charge density turned out to be more than tenfold higher than in neurons. Effects produced by [c3+]i/o were not in agreement with expectations based on screening or binding models.

Response to fibronectin-integrin interaction in leukaemia cells: delayed enhancing of a K+ current.

In murine erythroleukaemia cells, the response of ion channels was followed before and after contact with fibronectin-coated latex microspheres. Patch-clamp experiments in 'whole-cell' and in 'cell-attached' configurations showed that cell adhesion to fibronectin promoted plasma membrane hyperpolarization mediated by activation of potassium channels that were indistinguishable from calcium-dependent potassium channels K(Ca) in these cells. K+ current increase began in 5-6 min and was completed about 10 min after the first contact. The timecourse of this process recorded from 'whole-cell' was very similar to that followed in intact cells by observing the increase of single channel currents. The open probability of single channels in the patch increased after contact, revealing that this activation is propagated at distance from the adhesion site. The slow onset of the effect suggests the presence of a complex regulatory pathway between fibronectin-integrin binding and activation of potassium channels. Decreasing cytoplasmic free Ca2+ concentration to pCa 9 diminished, but did not inhibit, the response. The current induced by fibronectin was not blocked by apamin, alpha-charybdotoxin or glibenclamide, but was abolished by high concentrations of tetraethylammonium (TEA). These data suggest for the first time the existence of a specific regulative connection between integrin receptors and ionic channels.

Effects of inhibitors of ion-motive ATPases on the plasma membrane potential of murine erythroleukemia cells.

The membrane electric effects of N,N'-dicyclohexyl-carbodiimide (DCCD) and vanadate were studied in murine erythroleukemia cells (MELC), comparing the patch-clamp technique and the accumulation ratio (ARexp) of [3H]-tetraphenylphosphonium (TPP+). Electrophysiological measurements showed that both these inhibitors produce, at micromolar concentrations, a 20-30 mV hyperpolarization of resting potential (delta psi p) of MELC, which is abolished when the electrochemical equilibrium potential of K+ (EK) is brought close to zero. DCCD and vanadate turned out to have distinct targets on the plasma membrane of MELC (an H+ pump and the Na+,K(+)-ATPase, respectively). Measurements of ARexp showed that: (i) patch-clamp measurements of delta psi p were equivalent to those based on ARexp of antimycin-pretreated cells (ARANT); (ii) DCCD produced a strong increase in ARANT, that was antagonized by carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (FCCP) and diethylstilbestrol (DES); (iii) vanadate determined a marked increase in ARANT that was insensitive to FCCP, but antagonized by ouabain; (iv) incubation in high K+ medium (HK) brought ARANT to 1.0 in the controls, but did not lower this ratio below 3.0 in the presence of DCCD or vanadate; (v) the total amount of TPP+ taken up by the cells was in any case water extractable by a freezing and thawing procedure. On the whole, our data indicate that DCCD and vanadate hyperpolarize the MELC by increasing the K+ conductance and, at the same time, enhance the TPP+ binding, probably by changing the electrostatic potential profile of the plasma membrane. These effects seem to involve functional modifications of the target pumps, apparently related to the ion-occluding state of these enzymes.

Fibronectin-integrin binding promotes hyperpolarization of murine erythroleukemia cells.

The resting electrical potential (delta psi p) of murine erythroleukemia cells (MELC) was measured by the patch-clamp technique at different times after seeding onto culture surfaces enriched with bovine serum albumin (BSA) or Fibronectin (FN). While BSA did not produce significant changes of potential and cell shape, FN promoted a 15-20 mV hyperpolarization that preceded a marked cell spreading. This hyperpolarization was abolished by either treating cells with anti FN-receptor antibodies, or adding the RGDS tetrapeptide, suggesting that electric signals are elicited by the specific interaction of the FN cell binding domain with integrin receptors.