ABSTRACT
Hypertension is associated with abnormal neurohumoral activation. We tested the hypothesis that beta-adrenergic hyperresponsiveness in the sinoatrial node (SAN) of the spontaneously hypertensive rat occurs at the level of the L-type calcium current because of altered cyclic nucleotide-dependent signaling. Furthermore, we hypothesized that NO, a modulator of cGMP and cAMP, would normalize the beta-adrenergic phenotype in the hypertensive rat. Chronotropic responsiveness to norepinephrine (NE), together with production of cAMP and cGMP, was assessed in isolated atrial preparations from age-matched hypertensive and normotensive rats. Right atrial/SAN pacemaking tissue was injected with adenovirus encoding enhanced green fluorescent protein (control vector) or neuronal NO synthase (nNOS). In addition, L-type calcium current was measured in cells isolated from the SAN of transfected animals. Basal levels of cGMP were lower in hypertensive rat atria. These atria were hyperresponsive to NE at all of the concentrations tested, with elevated production of cAMP. This was accompanied by increased basal and norepinephrine-stimulated L-type calcium current. Using enhanced green fluorescent protein, we observed transgene expression within both tissue sections and isolated pacemaking cells. Adenoviral nNOS increased right atrial nNOS protein expression and cGMP content. NE-stimulated cAMP concentration and L-type calcium current were also attenuated by adenoviral nNOS, along with the chronotropic responsiveness to NE in hypertensive rat atria. Decreased calcium current after cardiac nNOS gene transfer contributes to the normalization of beta-adrenergic hyperresponsiveness in the SAN from hypertensive rats by modulating cyclic nucleotide signaling.
Subject(s)
Calcium Channels, L-Type/metabolism , Gene Transfer Techniques , Heart Rate , Hypertension/physiopathology , Nitric Oxide Synthase Type I/genetics , Receptors, Adrenergic, beta/metabolism , Sinoatrial Node/physiopathology , Adrenergic alpha-Agonists/pharmacology , Animals , Calcium Channels, L-Type/drug effects , Cyclic AMP/biosynthesis , Cyclic GMP/biosynthesis , Heart Atria , Heart Rate/drug effects , Hypertension/genetics , Male , Myocardium/metabolism , Nitric Oxide Synthase Type I/metabolism , Norepinephrine/pharmacology , Nucleotides, Cyclic/metabolism , Phenotype , Rats , Rats, Inbred SHR , Rats, Inbred WKY , Signal Transduction , Sinoatrial Node/metabolismABSTRACT
[reaction: see text] Cyclic tetrapeptides are an intriguing class of natural products. To synthesize highly strained cyclic tetrapeptides we developed a macrocyclization strategy that involves the inclusion of 2-hydroxy-6-nitrobenzyl (HnB) group at the N-terminus and in the "middle" of the sequence. The N-terminal auxiliary performs a ring closure/ring contraction role, and the backbone auxiliary promotes cis amide bonds to facilitate the otherwise difficult ring contraction. Following this route, the all-L cyclic tetrapeptide cyclo-[Tyr-Arg-Phe-Ala] was successfully prepared.
