Subcellular localization of nitric oxide (NO) synthases with effector molecules is an important regulatory mechanism for NO signalling. In the heart, NO inhibits L-type Ca2+ channels but stimulates sarcoplasmic reticulum (SR) Ca2+ release, leading to variable effects on myocardial contractility. Here we show that spatial confinement of specific NO synthase isoforms regulates this process. Endothelial NO synthase (NOS3) localizes to caveolae, where compartmentalization with beta-adrenergic receptors and L-type Ca2+ channels allows NO to inhibit beta-adrenergic-induced inotropy. Neuronal NO synthase (NOS1), however, is targeted to cardiac SR. NO stimulation of SR Ca2+ release via the ryanodine receptor (RyR) in vitro, suggests that NOS1 has an opposite, facilitative effect on contractility. We demonstrate that NOS1-deficient mice have suppressed inotropic response, whereas NOS3-deficient mice have enhanced contractility, owing to corresponding changes in SR Ca2+ release. Both NOS1-/- and NOS3-/- mice develop age-related hypertrophy, although only NOS3-/- mice are hypertensive. NOS1/3-/- double knockout mice have suppressed beta-adrenergic responses and an additive phenotype of marked ventricular remodelling. Thus, NOS1 and NOS3 mediate independent, and in some cases opposite, effects on cardiac structure and function.

Syndromic Hirschsprung disease has been associated with mutations in ZFHX1B, a Smad-interacting transcriptional repressor protein. Tissue in situ hybridization has demonstrated strong expression of ZFHX1B in the developing eye, suggesting that some mutations in this gene may cause visual loss. However, none of the reported mutations have been associated with an ocular phenotype. We describe a patient with Down syndrome and Hirschsprung disease with high myopia and ocular coloboma affecting the iris and retina. In addition to trisomy 21, a novel, de novo heterozygous A to G transition in exon 8 of the ZFHX1B gene was identified, which results in a R953G amino acid substitution. This abnormality was not seen in a screen of 200 chromosomes from ethnically matched, normal controls. The arginine residue at position 953 is an extremely conserved amino acid throughout evolution. This is the first report associating Hirschsprung disease and severe eye defects with a specific genetic mutation and is the first report of a mutation in ZFHX1B causing a developmental ocular anomaly.

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U s i n g a ' b u g t e n t ' ( b e l ow ) , b i r d -w a t c h e r s h o p e t o f i n d t a s t y t r e a t s t o e n t i c e t h e i v o r y -b i l l e d w o o d p e c k e r i n t o t h e o p e n i n t h e B i g W o o d s i n A r k a n s a s ( a b o v e ) .