Background-Adenylyl cyclases (ACs) are a family of effector molecules for G-protein-coupled receptors. The 2 ACs most abundantly expressed in cardiac myocytes are types 5 (AC5) and 6 (AC6), which have 65% amino acid homology. It has been speculated that coexpression of 2 AC types in cardiac myocytes represents redundancy, but the specific role of AC6 in cardiac physiology and its differences from AC5 remain to be defined. Methods and Results-We generated transgenic mice with targeted deletion of AC6. Deletion of AC6 was associated with reduced left ventricular contractile function (Pϭ0.026) and relaxation (Pϭ0.041). The absence of AC6 was associated with a 48% decay in ␤-adrenergic receptor-stimulated cAMP production in cardiac myocytes (Pϭ0.003) and reduced protein kinase A activity (Pϭ0.015). In addition, phospholamban phosphorylation was reduced (Pϭ0.015), sarcoplasmic reticulum Ca 2ϩ -ATPase activity was impaired (PϽ0.0001), and cardiac myocytes showed marked abnormalities in calcium transient formation (Pϭ0.001). Conclusions-The

Activation of the glucagon-like peptide (GLP)-1 receptor (GLP-1R) and inhibition of dipeptidyl peptidase-4 (DPP-4) are new antidiabetic strategies. The GLP-1R and DPP-4 are also expressed in the renal proximal tubular brush border, where they may regulate Na ϩ reabsorption. Exendin-4 (EX4) is a naturally occurring antidiabetic polypeptide (from the saliva of the lizard Heloderma suspectum) and GLP-1R agonist; however, part of its nonglucoregulatory effects are through GLP-1R-independent mechanisms. DPP-4 cleaves and inactivates GLP-1; thus the natriuretic effect of DPP-4 inhibition may be mediated by the GLP-1R. We report that parenteral application of EX4 in wild-type mice induced a diuresis and natriuresis associated with increases in glomerular filtration rate, fractional urinary fluid and Na ϩ excretion, and renal membrane expression of the Na ϩ /H ϩ exchanger NHE3 phosphorylated at S552 and S605, established consensus sites for cAMP-dependent PKA. These effects were absent in mice lacking the GLP-1R and independent of adenylyl cyclase 6. In comparison, parenteral application of the DPP-4 inhibitor alogliptin reduced plasma DPP-4 activity by 95% and induced a diuresis and natriuresis independent of the presence of the GLP-1R or changes in phosphorylated NHE3. The inhibitory effect on renal fluid and Na ϩ reabsorption of EX4, but not alogliptin, was preserved in diabetic db/db mice and associated with a modest reduction in blood pressure. These results reveal mechanistic differences in how EX4 vs. DPP-4 inhibition induces diuresis and natriuresis under normal states, with preservation of GLP-1R-mediated, but not DPP-4 inhibitor-dependent, natriuretic mechanisms in a mouse model of obese type 2 diabetes.glucagon-like peptide-1; dipeptidyl peptidase-4; NHE3; cAMP; proximal tubule GLUCAGON-LIKE PEPTIDE -1 (GLP-1), an incretin hormone secreted from enteroendocrine L cells in the intestine, stimulates glucose-dependent insulin release and may promote preservation of beta-cell function in patients with type 2 diabetes (9, 10). As a consequence, GLP-1 has been a principal focus of clinical and basic diabetes research in recent years. After secretion, active GLP-1 is rapidly cleaved by the widely expressed enzyme dipeptidyl peptidase-4 (DPP-4, CD26), such that the half-life of bioactive GLP-1 is Ͻ3 min. Therefore, therapeutic manipulation of the GLP-1 system includes strategies that inhibit the degradation of GLP-1 by DPP-4 (i.e., DPP-4 inhibitors) or degradation-resistant GLP-1 receptor (GLP-1R) agonists with a longer half-life, such as exendin-4 (EX4) or liraglutide.In addition to its metabolic effects, GLP-1 affects kidney function. Analysis of GLP-1R expression in rats (6), pigs, and humans (34) localized the GLP-1R to the brush border microvilli of proximal tubules. Intravenous infusion of GLP-1 increased glomerular filtration rate (GFR), inhibited proximal tubular reabsorption, and increased urine flow and Na ϩ excretion in rats (6, 30). In healthy subjects, infusion of GLP-1 evoked a dose-dependent increase in...

Background-We tested the hypothesis that intracoronary delivery of an adenovirus encoding adenylyl cyclase type VI (Ad.AC VI ) would be associated with increased left ventricular (LV) function in pigs with congestive heart failure. Methods and Results-Pigs (52Ϯ6 kg; nϭ16) underwent placement of pacemakers, LV pressure transducers, and left atrial and aortic catheters. Physiological and echocardiographic studies were obtained from conscious animals 13 days later, and pacing was initiated (220 bpm). Seven days later, measures of LV function were reduced, documenting severe LV dysfunction and dilation. Pigs then received intracoronary Ad.AC VI (1.4ϫ10 12 vp; nϭ7) or saline (PBS; nϭ9) (randomized, blinded), with concomitant infusion of nitroprusside (50 g/min, 6.4 minutes) to increase gene transfer. Pacing was continued for 14 days, and final studies were obtained. The a priori key end point was change in LV dP/dt during isoproterenol infusion (pre-Ad.AC VI value minus value after 21 days of pacing). Pigs receiving Ad.AC VI showed a smaller decrease in both LV ϩdP/dt (Pϭ0.0014) and LV ϪdP/dt (Pϭ0.0008). Serial echocardiography showed that Ad.AC VI treatment was associated with increased LV function and reduced LV dilation and that end-systolic wall stress was reduced. AC-stimulated cAMP production was increased 1.7-fold in LV samples from Ad.AC VI -treated pigs (Pϭ0.006), and B-type natriuretic peptide was reduced (0.035). Gene transfer was confirmed by polymerase chain reaction. Conclusions-AC