Phenylephrine acts via IP3-dependent intracellular NO release to stimulate L-type Ca2+ current in cat atrial myocytes

• Published in: The Journal of physiology 2005-08, Vol.567 (1), p.143-157
• Main Authors: Wang, Y. G., Dedkova, E. N., Ji, X., Blatter, L. A., Lipsius, S. L.
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Agonists - pharmacology; Animals; Calcium - metabolism; Calcium Channels - metabolism; Calcium Channels, L-Type - physiology; Calmodulin - metabolism; Cats; Cell Physiology; Female; Heart Atria - cytology; Inositol 1,4,5-Trisphosphate Receptors; Male; Microscopy, Electron; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - physiology; Myocytes, Cardiac - ultrastructure; Nitric Oxide - metabolism; Nitric Oxide Synthase - metabolism; Nitric Oxide Synthase Type III; Phenylephrine - pharmacology; Receptors, Cytoplasmic and Nuclear - metabolism; Sarcolemma - metabolism; Sarcolemma - ultrastructure; Signal Transduction - drug effects; Signal Transduction - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2005.090035

This study determined the effects of α 1 -adrenergic receptor (α 1 -AR) stimulation by phenylephrine (PE) on L-type Ca 2+ current ( I Ca,L ) in cat atrial myocytes. PE (10 μ m ) reversibly increased I Ca,L (51.3%; n = 40) and shifted peak I Ca,L activation voltage by −10 mV. PE-induced stimulation of I Ca,L was blocked by each of 1 μ m prazocin, 10 μ m l -NIO, 10 μ m W-7, 10 μ m ODQ, 2 μ m H-89 or 10 μ m LY294002, and was unaffected by 10 μ m chelerythrine or incubating cells in pertussis toxin (PTX). PE-induced stimulation of I Ca,L also was inhibited by each of 10 μ m ryanodine or 5 μ m thapsigargin, by blocking IP 3 receptors with 2 μ m 2-APB or 10 μ m xestospongin C or by intracellular dialysis of heparin. In field-stimulated cells, PE increased intracellular NO (NO i ) production. PE-induced NO i release was inhibited by each of 1 μ m prazocin, 10 μ m l -NIO, 10 μ m W-7, 10 μ m LY294002, 2 μ m H-89, 10 μ m ryanodine, 5 μ m thapsigargin, 2 μ m 2-APB or 10 μ m xestospongin C, and unchanged by PTX. PE (10 μ m ) increased phosphorylation of Akt, which was inhibited by LY294002. Confocal microscopy showed that PE stimulated NO i release from subsarcolemmal sites and this was prevented by 2 m m methyl-β-cyclodextrin, an agent that disrupts caveolae formation. PE also increased local, subsarcolemmal SR Ca 2+ release via IP 3 -dependent signalling. Electron micrographs of atrial myocytes show peripheral SR cisternae in close proximity to clusters of caveolae. We conclude that in cat atrial myocytes PE acts via α 1 -ARs coupled to PTX-insensitive G-protein to release NO i , which in turn stimulates I Ca,L . PE-induced NO i release requires stimulation of both PI-3K/Akt and IP 3 -dependent Ca 2+ signalling. NO stimulates I Ca,L via cGMP-mediated cAMP-dependent PKA signalling. IP 3 -dependent Ca 2+ signalling may enhance local SR Ca 2+ release required to activate Ca 2+ -dependent eNOS/NO i production from subsarcolemmal caveolae sites.