Contribution of caveolin protein abundance to augmented nitric oxide signaling in conscious dogs with pacing-induced heart failure

Myocardial NO signaling appears elevated in heart failure (HF). Whether this results from increased NO production, induction of the high-output NO synthase (NOS)2 isoform, or changes in NOS regulatory pathways (such as caveolae) remains controversial. We tested the hypothesis that increased abundance of caveolin-3 and/or sarcolemmal caveolae contribute to increased NO signaling in pacing-induced HF. Abundance of caveolin-3 (0.59+/-0.08 versus 0.29+/-0.08 arbitrary units, P=0.01) but not caveolin-1 was increased in HF compared with control conditions, assessed by Western blot, Additionally, transmission electron microscopy revealed increased caveolae (2.7+/-0.4 versus 1.3+/-0.3 per micrometer myocyte membrane, P<0.005). The association between caveolin-3 and NOS3 at the sarcolemma and T tubules was unchanged in HF compared with control myocytes. The impact of NOS inhibition with L-N-G-methylarginine hydrochloride (L-NMMA) on beta-adrenergic inotropy was assessed in conscious dogs before and after Hf. In control dogs, dobutamine (5 mu g . kg(-1) . min(-1)) increased +dP/dt by 36+/-7%, and this was augmented to 66+/-24% by 20 mg/kg L-NMMA (P=0.04 versus without L-NMMA, n=8) but not affected by 10 mg/kg L-NMMA (34+/-10%, P=NS; n=8). In I-IF, dobutamine +SdP/ldt response was depressed (P<0.001 versus control), and increased concentrations were required to match control inotropic responses (10 to 15 mu g . kg(-1) . min(-1), 48+/-7%). L-NMMA enhanced +dP/dt responses similarly at 10 mg/kg (61+/-17%, P=0.02; n=4) and 20 mg/kg (54+/-7%, P=0.04; n=7). Caveolin-3 abundance positively correlated with L-NMMA augmentation of dobutamine inotropic responses in HF (r=0.9, P=0.03; n=4). Thus, in canine pacing-induced HF, expression of caveolin-3 and of sarcolemmal caveolae is increased, This increase is associated with augmented agonist-stimulated NO signaling, likely via a compartmentation effect.