Rationale: Cardioprotective pathways may involve a mitochondrial ATP-sensitive potassium (mitoK ATP ) channel but its composition is not fully understood. Objective: We hypothesized that the mitoK ATP channel contains a sulfonylurea receptor (SUR)2 regulatory subunit and aimed to identify the molecular structure. Methods and Results: Western blot analysis in cardiac mitochondria detected a 55-kDa mitochondrial SUR2 (mitoSUR2) short form, 2 additional short forms (28 and 68 kDa), and a 130-kDa long form. RACE (Rapid Amplification of cDNA Ends) identified a 1.5-Kb transcript, which was generated by a nonconventional intraexonic splicing ( Key Words: K ATP channel Ⅲ SUR2 Ⅲ ischemia Ⅲ intraexonic splicing Ⅲ mitochondria A lternative splicing generates multiple mRNAs from a single gene, which are subsequently translated into diverse proteins with different structures and functions. 1 Up to 60% of mammalian genes are alternatively spliced. 2 Eukaryotic ion channel genes are known to have multiple splice variants. The ATP-sensitive potassium (K ATP ) channels are ubiquitously distributed in many tissue types. Sarcolemmal K ATP (sarcK ATP ) channels consist of a potassium inward-rectifier pore-forming subunit (Kir6.0) and a sulfonylurea receptor (SUR) regulatory subunit. 3 Various isoforms and splice variants for the SUR genes have been reported. 4,5 The cardiac muscle splice variant (SUR2A) differs from the vascular smooth muscle splice variant (SUR2B) in the alternative use of the SUR2 C-terminal exon. 6,7 Subtypes of splice variants for SUR2A or SUR2B that lack exon 14 or exon 17 exist in mice 7,8 and humans. 9 Moreover, sarcolemmal SUR short variants are found in heart 10 and pancreatic ␤ cells. 11,12 The copresence of multiple splice variants increases the functional diversity and genetic complexity of K ATP channels.In addition to a sarcolemmal location, 13 the K ATP channel is present in the inner membrane of mitochondria (mitoK ATP ). 14 Both forms of channels are involved in cardioprotective pathways, 15 but earlier pharmacological evidence suggests that the mitoK ATP channel is more critical in conferring protection. 16,17 However, the molecular composition of the mitoK ATP channel is uncertain, hampering present efforts in elucidating its role in preconditioning signaling. 18 Putative mitoK ATP channel subunits in the sizes of 55 and 63

The cardiac sarcolemmal ATP-sensitive potassium channel (K ATP ) consists of a Kir6.2 pore and a SUR2 regulatory subunit, which is an ATP-binding cassette (ABC) transporter. K ATP channels have been proposed to play protective roles during ischemic preconditioning. A SUR2 mutant mouse was previously generated by disrupting the first nucleotide-binding domain (NBD1), where a glibenclamide action site was located. In the mutant ventricular myocytes, a non-conventional glibenclamide-insensitive (10 μM), ATP-sensitive current (I KATPn ) was detected in 33% of singlechannel recordings with an average amplitude of 12.3±5.4 pA per patch, an IC 50 to ATP inhibition at 10 μM, and a mean burst duration at 20.6±1.8 ms. Newly designed SUR2-isoform or variantspecific antibodies identified novel SUR2 short forms in the sizes of 28 and 68 kDa in addition to a 150-kDa long form in the sarcolemmal membrane of wild-type (WT) heart. We hypothesized that channels constituted by these short forms that lack NBD1, confer I KATPn . The absence of the long form in the mutant corresponded to loss of the conventional glibenclamide-sensitive K ATP currents (I KATP ) in isolated cardiomyocytes and vascular smooth muscle cells but the SUR2 short forms remained intact. Nested exonic RT-PCR in the mutant indicated that the short forms lacked NBD1 but contained NBD2. The SUR2 short forms co-immunoprecipitated with Kir6.1 or Kir6.2 suggesting that the short forms may function as hemi-transporters reported in other eukaryotic ABC transporter subgroups. Our results indicate that different K ATP compositions may co-exist in cardiac sarcolemmal membrane.

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There is a gap in knowledge how maternal exposure to environmental tobacco smoke (ETS) is associated with offspring congenital heart defects (CHDs). In this case–control study, we collected data on 749 fetuses with CHDs and 880 fetuses without any congenital anomalies to examine the association of maternal ETS with fetal CHDs and the potentially moderating effect by maternal hazardous and noxious substances (HNS), periconceptional folate intake and paternal smoking. Maternal exposure to ETS in first trimester was associated with increased risk of CHDs in a dose–response gradient, with the AORs (95% CI) were1.38 (1.00–1.92), 1.60 (1.07–2.41), and 4.94 (2.43–10.05) for ETS < 1 h/day, 1–2 h/day, and ≥ 2 h/day, respectively. With the doubly unexposed group as reference categories, AORs for maternal ETS exposure ≥ 2 h/day in the absence of folate intake, in the presence of HNS exposure or paternal smoking, were 7.21, 11.43, and 8.83, respectively. Significant additive interaction between ETS exposure and maternal folate intake on CHDs was detected. Maternal ETS exposure during first trimester may increase the risk of offspring CHDs in a dose–response shape, and such effect may be modified by maternal folate intake or other potential factors.