Abstract
Signaling via endothelial nitric oxide synthase (NOS3) limits the heart's response to β-adrenergic (β-AR) stimulation, which may be protective against arrhythmias. However, mechanistic data are limited. Therefore, we performed simultaneous measurements of action potential (AP, using patch clamp), Ca2+ transients (fluo 4), and myocyte shortening (edge detection). L-type Ca2+ current (ICa) was directly measured by the whole cell ruptured patchclamp technique. Myocytes were isolated from wild-type (WT) and NOS3 knockout (NOS3-/-) mice. NOS3-/- myocytes exhibited a larger incidence of β-AR (isoproterenol, 1 μM)-induced early afterdepolarizations (EADs) and spontaneous activity (defined as aftercontractions). We also examined ICa, a major trigger for EADs. NOS3-/- myocytes had a significantly larger β-AR-stimulated increase in ICa compared with WT myocytes. In addition, NOS3 -/- myocytes had a larger response to β-AR stimulation compared with WT myocytes in Ca2+ transient amplitude, shortening amplitude, and AP duration (APD). We observed similar effects with specific NOS3 inhibition [L-N5-(1-iminoethyl)-ornithine (L-NIO), 10 μM] in WT myocytes as with NOS3 knockout. Specifically, L-NIO further increased isoproterenol- stimulated EADs and aftercontractions. L-NIO also further increased the isoproterenol-stimulated ICa, Ca2+ transient amplitude, shortening amplitude, and APD (all P < 0.05 vs isoproterenol alone). L-NIO had no effect in NOS3-/- myocytes. These results indicate that NOS3 signaling inhibits the β-AR response by reducing ICa and protects against arrhythmias. This mechanism may play an important role in heart failure, where arrhythmias are increased and NOS3 expression is decreased.
Original language | English (US) |
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Pages (from-to) | H1473-H1480 |
Journal | American Journal of Physiology - Heart and Circulatory Physiology |
Volume | 294 |
Issue number | 3 |
DOIs | |
State | Published - Mar 2008 |
Externally published | Yes |
Keywords
- Action potential
- Cardiac myocytes
- Early afterdepolarizations
- Endothelial nitric oxide synthase
ASJC Scopus subject areas
- Physiology
- Cardiology and Cardiovascular Medicine
- Physiology (medical)