Regulation of nitric oxide synthesis by beta‐adrenergic receptors in the nuclear envelope

Abstract

Both β‐adrenergic receptors (β‐ARs) and endothelin receptors (ETRs) have been shown to be present on nuclear membranes in adult cardiac ventricular myocytes. These nuclear‐localized receptors are functional with respect to ligand binding and effector activation. Furthermore, isoproterenol (ISO) increases transcription initiation in isolated nuclei whereas endothelin‐1 (ET‐1) has the opposite effect. Here we investigate whether ISO and ET‐1 regulate nitric oxide (NO) production in nuclear membranes. Isolated nuclei were incubated with a fluorescent NO indicator, 4,5‐diaminofluorescein (DAF‐2), followed by either ET‐1 or ISO treatment. In both cases, an increase in DAF‐2 fluorescence was observed: this increase was inhibited by the NO synthase inhibitor, L‐NAME. Pertussis toxin treatment also increased DAF‐2 fluorescence. The PKB inhibitor triciribine, which converts ISO from an activator of transcription to an inverse agonist, potentiated ISO‐mediated DAF‐2 fluorescence without affecting ET‐1 signalling. These experiments were repeated in intact myocytes using caged analogues of ISO and ET‐1, and in combination with 4,5‐diaminofluorescein diacetate (DAF‐2 DA), a cell‐permeant form of DAF‐2. Our results suggest the nuclear β‐ARs and ETRs regulate NO synthesis.