Abstract-Previous studies have demonstrated a role for voltage-gated K ϩ (Kv) channel ␣ subunits of the Kv4 subfamily in the generation of rapidly inactivating/recovering cardiac transient outward K ϩ current, I to,f , channels. Biochemical studies suggest that mouse ventricular I to,f channels reflect the heteromeric assembly of Kv4.2 and Kv4.3 with the accessory subunits, KChIP2 and Kv␤1, and that Kv4.2 is the primary determinant of regional differences in (mouse ventricular) I to,f densities. Interestingly, the phenotypic consequences of manipulating I to,f expression in different mouse models are distinct. In the experiments here, the effects of the targeted deletion of Kv4. 1 Considerable progress has been made in characterizing the properties of myocardial Kv channels and in defining the roles of individual Kv channel pore-forming (␣) and accessory (␤) subunits in the generation of these channels. 1 In adult mouse ventricles, for example, multiple Kv currents are coexpressed. 2-10 All available evidence suggests that ␣ subunits of the Kv4 subfamily underlie fast inactivating and recovering cardiac transient outward, I to,f , channels. 1 Biochemical studies suggest that mouse ventricular I to,f channels reflect the heteromeric assembly of Kv4.2 and Kv4.3. 10 In large mammals, however, Kv4.2 is not expressed, and I to,f channels are thought to reflect Kv4.3 homotetramers. 11,12 Multiple splice variants of Kv4.3 have been identified, 12 although the role(s) of these variants in the generation of I to,f channels is unclear.The accessory subunit, KChIP2, 13 coimmunoprecipitates with Kv4.2 and Kv4.3 from adult mouse ventricles, 10 and it has been reported that I to,f is eliminated in ventricular myocytes isolated from mice in which the KChIP2 locus was disrupted. 14 In canine ventricles, KChIP2 message 15,16 and protein 17 expression parallel variations in I to,f densities, suggesting that KChIP2 is the primary determinant of I to,f gradients. 15,17 In rodent ventricles, however, KChIP2 is uniformly expressed, and regional differences in I to,f densities are correlated with heterogeneities in Kv4.2 expression. 10,18 Interestingly, the phenotypic consequences of manipulating I to,f expression in vivo are distinct. 4,7,14,19 Recordings from ventricular myocytes isolated from transgenic mice expressing a pore mutant of Kv4.2, Kv4.2W362F, that functions as a dominant negative (Kv4.2DN), for example, revealed that I to,f is eliminated. 4 Materials and MethodsAnimals were handled in accordance with the NIH Guide for the Care and Use of Laboratory Animals; all protocols were approved by the Washington University Animal Studies Committee. The generation of the Kv4.2 Ϫ/Ϫ mice and the methods/protocols used in the present study are detailed in the online data supplement available at http://circres.ahajournals.org. Results Targeted Disruption of the KCND2 (Kv4.2) LocusIn the targeting construct used to generate Kv4.2 Ϫ/Ϫ mice ( Figure 1A), described in the expanded Materials and Methods section in the online data supp...

The aim of this study was to investigate the dose-dependent effect of pretreatment with the selective sodium-hydrogen exchange NHE-subtype 1 inhibitor cariporide on myocardial infarct mass in a rabbit model of coronary ligation and reperfusion. Furthermore, in a second part of the study, we tested the effect of cariporide in the rabbits when given prior to reperfusion. Rabbits (n=49) were randomized in 7 groups: saline vehicle, cariporide: 0.01, 0.03, 0.1 and 0.3 mg/kg, and subjected to a 30 min occlusion of a branch of the left coronary artery followed by 2 h reperfusion. Cariporide was given as a bolus intravenously 10 min before occlusion or 5 min before reperfusion. After reperfusion, myocardial infarct mass was determined by triphenyl tetrazolium chloride staining and expressed as a percent of area at risk. Cariporide given intravenously 10 min before occlusion in doses of 0.01, 0.03, 0.1, 0.3 mg/kg, led to a dose-dependent reduction in infarct mass from 58+/-6% in controls to 48+/-4% (-17%, NS), 36+/-5% (-38%, p<0.05), 26+/-6% (-55%, p<0.05), 11+/-4% (-81%, p<0.05) respectively, whereas area at risk did not differ in between the groups. The effect of the lowest dose of 0.01 mg/kg did not reach significance. Plasma levels at different doses of cariporide were correlated to the respective infarct mass. After coronary occlusion left ventricular end-diastolic pressure (LVEDP) significantly increased throughout occlusion and reperfusion. Cariporide in the doses of 0.3, 0.1 and 0.03 mg/kg normalized LVEDP when measured after 2 h reperfusion. In controls hemodynamic parameters such as mean arterial blood pressure (MAP), heart rate (HR), left ventricular pressure (LVP) and LV dP/dt(max) were not significantly changed by ischemia/reperfusion with the exception of MAP, LVP and LV dP/dt(max) which were significantly decreased after 120 min reperfusion. Cariporide at doses of 0.1, 0.03 and 0.01 mg/kg did not significantly influence these parameters, whereas the highest dose of 0.3 mg/kg prevented the decrease of MAP and LVP. Cariporide (0.3 mg/kg i.v.) administered 5 min before reperfusion significantly reduced infarct mass by 31%. Under these conditions the increase of LVEDP after coronary occlusion was not influenced by cariporide. As in the pretreatment experiments, the decrease of MAP and LVP was prevented when measured 2 h after reperfusion. The results show that pretreatment with the NHE-subtype 1 inhibitor cariporide is cardioprotective by reducing infarct mass in rabbits in a dose-dependent manner. While the cardioprotective effect of pretreatment could be demonstrated over a broad range of doses, the efficacy of the compound when given only on reperfusion was significant but more limited.