OATP2B1 is a high-affinity uptake transporter for atorvastatin and is expressed in the vascular endothelium of the human heart, suggesting its involvement in cardiac uptake of atorvastatin.

The present study based on auricular samples suggests that genetic factors play a rather limited role in modulating P-gp expression in human heart. Therefore, the substantial interindividual variability in cardiac P-gp expression is likely related to environmental or disease related factors.

S U M M A R Y Efforts to improve severely impaired myocardial function include transplantation of autologous hematopoietic side population (SP) stem cells. The transmembrane ABCtype (ATP binding cassette) half-transporter ABCG2 (BCRP) serves as a marker protein for SP cell selection. We have recently shown that other ABC transport proteins such as ABCB1 and ABCC5 are differentially expressed in normal and diseased human heart. Here we investigated localization and individual ABCG2 expression in 15 ventricular (including 10 cardiomyopathic) and 51 auricular heart tissue samples using immunohistochemistry, confocal laser scanning fluorescence microscopy, and real-time RT-PCR. Individual genotypes were assigned using PCR-restriction fragment length polymorphism (RFLP) analysis and subsequently correlated to ABCG2 mRNA levels. ABCG2 was localized in endothelial cells of capillaries and arterioles of all samples. Ventricular samples from cardiomyopathic hearts exhibited significantly increased levels of ABCG2 mRNA (ABCG2/18S rRNA: 1.08 6 0.30 3 10 27

The multidrug resistance protein 5 (MRP5/ABCC5) has been recently identified as cellular export pump for cyclic nucleotides with 3',5'-cyclic GMP (cGMP) as a high-affinity substrate. In view of the important role of cGMP for cardiovascular function, expression of this transport protein in human heart is of relevance. We analyzed the expression and localization of MRP5 in human heart [21 auricular (AS) and 15 left ventricular samples (LV) including 5 samples of dilated and ischemic cardiomyopathy]. Quantitative real-time polymerase chain reaction normalized to beta-actin revealed expression of the MRP5 gene in all samples (LV, 38.5 +/- 12.9; AS, 12.7 +/- 5.6; P < 0.001). An MRP5-specific polyclonal antibody detected a glycoprotein of approximately 190 kd in crude cell membrane fractions from these samples. Immunohistochemistry with the affinity-purified antibody revealed localization of MRP5 in cardiomyocytes as well as in cardiovascular endothelial and smooth muscle cells. Furthermore, we could detect MRP5 and ATP-dependent transport of [(3)H]cGMP in sarcolemma vesicles of human heart. Quantitative analysis of the immunoblots indicated an interindividual variability with a higher expression of MRP5 in the ischemic (104 +/- 38% of recombinant MRP5 standard) compared to normal ventricular samples (53 +/- 36%, P < 0.05). In addition, we screened genomic DNA from our samples for 20 single-nucleotide polymorphisms in the MRP5 gene. These results indicate that MRP5 is localized in cardiac and cardiovascular myocytes as well as endothelial cells with increased expression in ischemic cardiomyopathy. Therefore, MRP5-mediated cellular export may represent a novel, disease-dependent pathway for cGMP removal from cardiac cells.

SUMMARY1. The effects of histamine were investigated on mechanical and electrophysiological parameters in isolated electrically driven human ventricular papillary muscles. The effects of cimetidine and propranolol on histamine responses were also investigated.2. The effects ofhistamine were compared with those ofnoradrenaline, isoprenaline, dimaprit, a selective H2-receptor agonist, and a cyclic AMP derivative, 8-(4-chlorphenylthio) cyclic AMP.3. The effects of histamine and dimaprit and the effects of cimetidine on histamine responses were also investigated in guinea-pig right ventricular papillary muscles in order to allow a comparison with human papillary muscles.4. In human papillary muscles, histamine caused concentration-dependent increases in the force of contraction and reductions in both time-to-peak tension and time-to-half-maximal relaxation. Histamine simultaneously caused distinct changes in the action potential configuration with increases in the height and duration of the plateau phase and an increase in the over-all action potential duration.5. Noradrenaline and isoprenaline produced similar responses to histamine, as did 8-(4-chlorphenylthio) cyclic AMP, consistent with the view that the effects of histamine as well as the fi-adrenoceptor agonists on human ventricle, were associated with cyclic AMP mediated increases in calcium-dependent slow inward current.

Observations among Karlsburg patients in 2006 revealed that the majority of very low platelet levels inducing postoperative heparin-induced-thrombocytopenia (HIT)-diagnostics with at the end negative results appeared related to aortic valve replacement (AVR) with stentless bioprostheses. We compared the postoperative courses of platelet counts in patients having had AVR with stentless prostheses (Sorin Biomedica Freedom Solo [SOLO]) or stented prostheses (Carpentier Edwards Perimount [PM]). Between February 2005 and April 2007, 209 patients received AVR with SOLO, in 137 patients a PM-prosthesis was implanted. The mean platelet levels were compared from the first up to the fifth postoperative day. A higher occurrence of platelet levels below 100 Gpt/l between the second and the fifth postoperative day was found in the SOLO-group (71.9%) compared with the other biological substitute PM (36.6%). Differences in platelet counts between SOLO- and PM-subgroups were measured for day 2 (P=0.03), day 3 (P=0.0004) day 4 (P=0.0007), day 5 (P=0.0002) and at discharge (P<0.0001). Following intervention with conventional biological AVR, differences in the postoperative recovery of platelet counts can be detected, depending on the prosthesis used. The causes for and the clinical implications of this phenomenon are not yet assessed.

Background-To date, the uptake of drugs into the human heart by transport proteins is poorly understood. A candidate protein is the organic cation transporter novel type 2 (OCTN2) (SLC22A5), physiologically acting as a sodiumdependent transport protein for carnitine. We investigated expression and localization of OCTN2 in the human heart, uptake of drugs by OCTN2, and functional coupling of OCTN2 with the eliminating ATP-binding cassette (ABC) transporter ABCB1 (P-glycoprotein). Methods and Results-Messenger RNA levels of OCTN2 and ABCB1 were analyzed in heart samples by quantitative polymerase chain reaction. OCTN2 was expressed in all auricular samples that showed a pronounced interindividual variability (35 to 1352 copies per 20 ng of RNA). Although a single-nucleotide polymorphism in OCTN2 (G/C at position Ϫ207 of the promoter) had no influence on expression, administration of ␤-blockers resulted in significantly increased expression. Localization of OCTN2 by in situ hybridization, laser microdissection, and immunofluorescence microscopy revealed expression of OCTN2 mainly in endothelial cells. For functional studies, OCTN2 was expressed in Madin-Darby canine kidney (MDCKII) cells. Using this system, verapamil, spironolactone, and mildronate were characterized both as inhibitors (EC 50 ϭ25, 26, and 21 mol/L, respectively) and as substrates. Like OCTN2, ABCB1 was expressed preferentially in endothelial cells. A significant correlation of OCTN2 and ABCB1 expression in the human heart was observed, which suggests functional coupling. Therefore, the interaction of OCTN2 with ABCB1 was tested with double transfectants. This approach resulted in a significantly higher transcellular transport of verapamil, a substrate for both OCTN2 and ABCB1. Conclusions-OCTN2 is expressed in the human heart and can be modulated by drug administration. Moreover, OCTN2can contribute to the cardiac uptake of cardiovascular drugs.

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