Abstract␤ 1 -and ␤ 2 -adrenoceptors in heart muscle cells mediate the catecholamine-induced increase in the force and frequency of cardiac contraction. Recently, in addition, we demonstrated the functional expression of ␤ 3 -adrenoceptors in the human heart. Their stimulation, in marked contrast with that of ␤ 1 -and ␤ 2 -adrenoceptors, induces a decrease in contractility through presently unknown mechanisms. In the present study, we examined the role of a nitric oxide (NO) synthase pathway in mediating the ␤ 3 -adrenoceptor effect on the contractility of human endomyocardial biopsies. The negative inotropic effects of a ␤ 3 -adrenoceptor agonist, BRL 37344, and also of norepinephrine in the presence of ␣ -and

Administration of CHIKV immunoglobulins may constitute a safe and efficacious prevention strategy and treatment for individuals exposed to CHIKV who are at risk of severe infection, such as neonates born to viremic mothers and adults with underlying conditions. These results provide a proof-of-concept for purifying human immunoglobulins from plasma samples from patients in the convalescent phase of an emerging infectious disease for which neither prevention nor treatment is available.

This study was conducted to evaluate whether treatment of normal and diabetic rat hearts with rosiglitazone, a high-affinity ligand of the peroxisome proliferator-activated receptor-␥ (PPAR-␥) used for the treatment of type 2 diabetes, improves postischemic functional recovery. The effects of acute rosiglitazone administration were investigated using working hearts isolated from normal rat or rats diabetic for 4 weeks after streptozotocin (STZ) injection. Hearts were subjected to 30 min of normothermic, zero-flow ischemia followed by 30-min reperfusion. Rosiglitazone (1 mol/l) administered before ischemia had no effect on cardiac function during baseline perfusion, but it significantly improved aortic flow during reperfusion in both normal and diabetic hearts. In a chronic protocol in which rosiglitazone was given by daily gavage (10 mol/kg body wt) immediately after STZ injection, rosiglitazone also prevented postischemic injury and significantly improved functional recovery. Using Western immunoblotting, it was demonstrated that the acute cardioprotective effect of rosiglitazone is associated with an inhibition of Jun NH 2 -terminal kinase phosphorylation in both normal and diabetic rat hearts. Furthermore, rosiglitazone also inhibited activating protein-1 DNAbinding activity. These data, demonstrating that rosiglitazone limits postischemic injury in isolated hearts, suggest an important function for PPAR-␥ in the heart. Diabetes

Our group recently cloned the electrogenic Na+-[Formula: see text]cotransporter (NBC) from salamander kidney and later from mammalian kidney. Here we report cloning an NBC isoform (hhNBC) from a human heart cDNA library. hhNBC is identical to human renal NBC (hkNBC), except for the amino terminus, where the first 85 amino acids in hhNBC replace the first 41 amino acids of hkNBC. About 50% of the amino acid residues in this unique amino terminus are charged, compared with ∼22% for the corresponding 41 residues in hkNBC. Northern blot analysis, with the use of the unique 5′ fragment of hhNBC as a probe, shows strong expression in pancreas and expression in heart and brain, although at much lower levels. In Xenopus oocytes expressing hhNBC, adding 1.5% CO2/10 mM[Formula: see text] hyperpolarizes the membrane and causes a rapid fall in intracellular pH (pHi), followed by a pHi recovery. Subsequent removal of Na+ causes a depolarization and a reduced rate of pHi recovery. Removal of Cl− from the bath does not affect the pHi recovery. The stilbene derivative DIDS (200 μM) greatly reduces the hyperpolarization caused by adding CO2/[Formula: see text]. In oocytes expressing hkNBC, the effects of adding CO2/[Formula: see text]and then removing Na+ were similar to those observed in oocytes expressing hhNBC. We conclude that hhNBC is an electrogenic Na+-[Formula: see text]cotransporter and that hkNBC is also electrogenic.

Our data provide evidence that inhibition of hhNBC, whose role in cardiac pathologies could be amplified by overexpression, represents a novel therapeutic approach for ischemic heart disease.

Endothelin (ET) has been shown to be elevated under conditions of cardiac pathology and to produce diverse cardiac effects, including coronary constriction and a positive inotropic influence. We characterized the concentration- and time-dependent effects of the most potent of the ET isoforms, ET-1 (0.4, 2, and 4 nmol/L), on myocardial contractility and coronary resistance and assessed its effects on the ischemic and reperfused heart. Because ET-1 has been shown to activate the Na(+)-H+ exchanger in cardiac myocytes, we determined the contribution of the antiport by examining the effects of ET-1 in the presence of the Na(+)-H+ exchange inhibitor methylisobutyl amiloride (MIA). At all three concentrations, ET-1 produced an initial positive inotropic effect that was reversed with continued perfusion, the degree of the reversal being dependent on ET-1 concentration. With 0.4 nmol/L, contractility returned to pre-ET-1 values, whereas after 75 minutes of perfusion with 4 nmol/L ET-1, contractility was depressed by 75%. At all concentrations, ET-1 produced a coronary-constricting effect, whereas an elevation in resting tension was observed only with 4 nmol/L ET-1. MIA significantly prevented the positive inotropic effect of ET-1 but had no effect on loss in function or elevation in resting tension produced by 4 nmol/L ET-1. Furthermore, MIA partially, but not significantly, attenuated the constricting effects of all ET-1 concentrations. In the ischemic heart, 0.4 nmol/L ET-1 appeared to delay the loss in contractility produced by cessation of flow, although the effect was not significant. Higher concentrations of ET-1 were without effect on ischemia-induced contractile depression, although their presence produced a marked elevation in resting tension during ischemia that was attenuated by MIA. Recovery in contractility was reduced by all concentrations of ET-1, although the effects of the lowest concentration were associated primarily with defective relaxation. The depressant effects of ET-1 either in normal or ischemic/reperfused hearts were irreversible. The inhibitory effects of ET-1 on contractile recovery were associated with diminished tissue glycogen and elevated lactate levels. High-energy phosphates after reperfusion were depressed in hearts treated with 4 nmol/L ET-1. The attenuation in contractile recovery and alterations in metabolite content were prevented by MIA. These results provide evidence that ET-1 produces complex effects on heart function that are likely mediated via different mechanisms and demonstrate its ability to aggravate ischemic and reperfusion injury through a mechanism possibly involving Na(+)-H+ exchange activation.

The comparison of data from diabetic rat hearts with reduced activity of the Na+/H+ exchange process v normal hearts with pharmacological block of the exchanger provide support for a critical role of the Na+/H+ exchanger in the initial stage of reperfusion.

1 This study aimed to determine the role of the vascular endothelium on recovery of contractile function following global low-flow ischaemia of guinea-pig isolated working hearts and the effects of adenosine analogues on this recovery. 2 Guinea-pig isolated spontaneously beating or paced working hearts were set up and coronary flow (CF), aortic output (AO) (as an index of cardiac function), heart rate (HR), left ventricular pressure (LVP) and dP/dt max recorded. The endothelium was either intact or removed by a blast of oxygen. 3 In spontaneously beating hearts, low-flow ischaemia for 30 min reduced CF and cardiac contractility (LVP, dP/dt max) but not AO. On reperfusion, CF, LVP and dP/dt max recovered, while AO fell precipitously followed by a gradual recovery, indicative of myocardial stunning. The effects of ischaemia did not differ between endothelium-intact and -denuded hearts, indicating no role of the endothelium in the changes observed. 4 The adenosine analogues, N6-cyclopentyladenosine (CPA, A1 selective), 5'-N-ethylcarboxamidoadenosine (NECA, two-fold A2 selective over A1) and 2-p-((carboxyethyl)-phenethylamino)-5'carboxamidoadenosine (CGS21680, A2A selective) were infused (3 x 10-7 M) from 10 min into the 30-min low-flow ischaemia of denuded hearts and during reperfusion. 5 CGS21680 increased CF and improved the postischaemic functional recovery, as measured by the AO. NECA and CPA were not cardioprotective. The A2A selective antagonist, ZM241385, attenuated the coronary vasodilatation by CGS21680 and abolished the improved recovery of AO on reperfusion. 6 Reperfusion of paced working hearts caused a dramatic fall in AO which failed to recover. Infusion of CGS21680 from 15 min into the ischaemic period produced vasodilatation but failed to restore AO, presumably because the ischaemic damage was irreversible. 7 Thus, the endothelium plays no role in myocardial dysfunction following low-flow global ischaemia and reperfusion of guinea-pig working hearts. The A2A adenosine receptor-selective agonist but not the non-selective A2 receptor agonist, NECA, attenuated ischaemia- and reperfusion-induced stunning. This was attributed to increased CF and was independent of the endothelium.