Sepsis affects cardiac expression of multidrug resistance protein 5 (MRP5, ABCC5), an ABC-type CGMP export pump.

One of the clinical characteristics associated with septic shock is heart failure. Several lines of evidence indicate that functional consequences of heart failure in septic shock are linked to the activated NO-cyclic guanosine monophosphate (NO-cGMP) pathway. We have previously shown that the high-affinity cGMP export transporter, multidrug resistance protein 5 (MRP5), is expressed in the heart, which modulates intracellular concentrations and, hence, the effects of cGMP. Thus, modified expression of cardiac MRP5 in septic shock can alter cGMP concentrations and contribute to the development of heart failure. We therefore investigated MRP5 expression in the heart using two established murine models of septic shock (intraperitoneal LPS injection and surgical implantation of a stent into the ascending colon, resulting in a multibacterial peritonitis [CASP, colon ascendens stent peritonitis] in C57BL/6N mice, respectively; n = 38). Cardiac MRP5 was assessed by quantitative polymerase chain reaction and immunofluorescence. The protein was localized in the endothelial wall, smooth muscle, and cardiac myocytes. MRP5 mRNA expression was significantly reduced compared with controls both in the LPS (31.9 +/- 16.8 x 10(-4) vs. 54.1 +/- 14.8 x 10(-4), P = 0.025) and CASP model (18.3 +/- 9.4 x 10(-4) vs. 42.8 +/- 12.1 x 10(-4), P = 0.009; MRP5/glyceraldehyde 3-phosphate dehydrogenase copy numbers, respectively). In parallel, IL-6 plasma levels were significantly increased in both models. Incubation of cultured murine cardiomyocytes (HL1) with 5 ng/mL IL-6 resulted in decreased expression of MRP5 (54% of control), as did incubation of the cells with serum from septic mice (LPS serum, 22% of control; CASP serum, 11% of control). In conclusion, cardiac expression of the cGMP export transporter MRP5 is decreased in two murine models of septic shock, most likely by a transcriptional mechanism. Reduced cGMP export as a consequence of decreased MRP5 expression can attenuate heart failure in sepsis.

Uptake of cardiovascular drugs into the human heart: expression, regulation, and function of the carnitine transporter OCTN2 (SLC22A5).

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 sodium-dependent 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 -207 of the promoter) had no influence on expression, administration of beta-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 (EC50=25, 26, and 21 micromol/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, OCTN2 can contribute to the cardiac uptake of cardiovascular drugs.

Expression, localization, and function of MRP5 (ABCC5), a transporter for cyclic nucleotides, in human placenta and cultured human trophoblasts: effects of gestational age and cellular differentiation.

The placenta functions both as site for nutrition and protection of the fetus. Transport proteins, including members of the multidrug resistance protein (MRP)/ABCC subfamily, have been recognized to contribute to the latter function. MRP5 (ABCC5) was identified as transmembrane transport protein for cyclic nucleotides, especially 3',5'-cyclic GMP (cGMP), indicating an additional role in signal transduction and a potential role in placenta development. We therefore studied expression, localization, and function of MRP5 in placenta of different gestational ages. Quantitative real-time polymerase chain reaction revealed expression of MRP5 in all 60 samples from pre-term and term placenta, with a decreasing mean expression with gestational age (MRP5/18S-ratio x 1000; < 32 weeks: 2.91 +/- 0.73, n = 15; 32 to 37 weeks: 2.10 +/- 0.87, n = 15; > 37 weeks: 0.46 +/- 0.08, n = 30; P < 0.01). Immunofluorescence microscopy with an anti-MRP5 antibody indicated localization of MRP5 preferentially in the basal membrane of syncytiotrophoblasts and in and around fetal vessels. ATP-dependent [(3)H]cGMP transport as evidence for MRP5 function could be demonstrated in isolated basal membrane vesicles. Moreover, the influence of cellular differentiation on MRP5 expression was studied in isolated trophoblasts, revealing an increase of the MRP5 expression in parallel with the hCG production (MRP5/18S-ratio x 1000 was 2.4 +/- 0.5 at day 5 of culture and 1.45 +/- 0.5 at day 0 of culture, n = 3 preparations, significant difference with P < 0.05). In conclusion, MRP5 expression depends on gestational age and varies throughout the differentiation process. In view of the important role of cGMP for cellular differentiation, MRP5 may play a role in placental development in context with a specific need for cellular cGMP export.