Adrenergic Stimulation Regulates Na+/Ca2+Exchanger Expression in Rat Cardiac Myocytes

Increased susceptibility to ventricular arrhythmias is associated with changes in Ca2+ regulatory proteins in paraplegic rats

“…The authors demonstrated that the increased Na/Ca exchanger expression was mediated via cAMP-dependent increases in the transcription initiation rate. The increased abundance of the Na/Ca exchanger may be secondary to increases in intracellular Ca 2ϩ and not the direct action of ␤-adrenergic receptor stimulation, because the increased abundance occurred with increased intracellular Ca 2ϩ (12). The authors also demonstrated a functional significance for the adrenergic receptor-mediated increase in the Na/Ca exchanger.…”

“…Previous reports have documented that adrenergic receptor stimulation enhances the expression of the Na/Ca exchanger in vivo and in vitro (12,13). For example, Na/Ca exchanger message and protein abundance were increased in the presence of the ␤-adrenergic receptor agonist isoproterenol (12).…”

“…Furthermore, adrenergic receptor activation alters the expression of genes that encode cardiac Ca 2ϩ regulatory proteins (13,29). The ability of cardiac myocytes to maintain cytosolic Ca 2ϩ concentration within a tightly controlled range is crucial for cardiac electrical stability (12). Thus individuals with paraplegia may have alterations in the regulation of multiple ionic mechanisms including Ca 2ϩ homeostasis that lead to an increased susceptibility to ventricular arrhythmias.…”

Acute actions of testosterone on contractile function of isolated rat ventricular myocytes

“…Four 60-day-old male Sprague -Dawley rats were housed individually, fed and watered ad libitum and maintained on a 12-h light/dark cycle at 238C. Single ventricular myocytes were isolated enzymatically as described previously (11). Briefly, hearts were rapidly removed and perfused (at 378C) with Krebs -Henseleit bicarbonate (KHB) buffer containing 118 mM NaCl, 4.7 mM KCl, 1.25 mM CaCl 2 , 1.2 mM MgSO 4 , 1.2 mM KH 2 PO 4 , 25 mM NaHCO 3 , 10 mM Hepes and 11.1 glucose.…”

“…Mechanical properties of ventricular myocytes isolated from four 60-day-old male rats were assessed using a SoftEdge video-based edge-detection system (IonOptix Corporation, Milton, MA, USA) (11). In brief, cells were placed in a Warner chamber mounted on the stage of an inverted microscope (Olympus, IX-70) and superfused (approximately 1 ml/min at 378C) with a buffer containing 131 mM NaCl, 4 mM KCl, 1 mM CaCl 2 , 1 mM MgCl 2 , 10 mM glucose and 10 mM Hepes (pH 7.4).…”