Intrinsic Cardiac Catecholamines Help Maintain Beating Activity in Neonatal Rat Cardiomyocyte Cultures

Abstract

In the present study, we identify intrinsic cardiac adrenergic (ICA) cells in the neonatal rat heart using immunofluorescent histochemical staining techniques with antibodies that specifically recognize the major enzymes in the catecholamine biosynthetic pathway. ICA cells are most concentrated near the endocardial surface of ventricular myocardium, but are also found sporadically throughout the heart. In primary cultures of neonatal rat cardiomyocytes, ICA cells are closely associated with clusters of cardiomyocytes. To investigate a potential role for intrinsically produced catecholamines, we recorded beating rates in the presence and absence of the catecholamine-depleting agent reserpine or the adrenergic receptor blockers prazosin and timolol using videomicroscopy and photodiode sensors. Our results show that beating rates slow significantly when endogenous catecholamines are depleted or when their action is blocked with either a ␤-or an ␣ 1 -adrenergic receptor antagonist. These data indicate that intrinsic cardiac catecholamines help to maintain beating rates in neonatal rat cardiomyocyte cultures via stimulation of ␣ 1 -and ␤-adrenergic receptors. This information should help to increase our understanding of the physiologic mechanisms governing cardiovascular function in neonates. The catecholamines epinephrine and norepinephrine are neurotransmitter stress hormones that influence cardiac function profoundly. We and others have shown that the heart itself produces these catecholamines in specialized cells known as ICA cells (1-3). We have also shown that these cells are transiently and progressively associated with different regions of the embryonic rat heart that are important sites for pacemaking and conduction tissue development (e.g. sinoatrial node, atrioventricular canal, bundle of His, and ventricular septum) (3). ICA cells appear to persist in the heart postnatally as they have been found in neonatal (1, 4 -6) and adult (1, 7-11) hearts. In adult hearts, ICA cells are often found clustered around sites of innervation (6, 7, 10). In the neonate, sympathetic innervation of the heart is incomplete (12), and little is known about the specific distribution of ICA cells in the heart (13-15). Further, the functional significance of these ICA cells in the neonatal (or adult) heart is unknown.The neonatal period is characterized by dramatic cardiovascular adaptation to extrauterine life. Although peripheral catecholamines are synthesized by the adrenal medulla (16 -18) and organ of Zuckerkandl (19,20) in the perinatal period, functional sympathetic innervation of the heart is not completed until the second week after birth in rats (15, 21). The neonatal rat heart, nevertheless, expresses fully functional ␣-and ␤-adrenergic receptors, allowing for chronotropic responses to either ␣ 1 -or ␤-adrenergic agonists (22-24). Once functional sympathetic innervation of the heart is achieved, ␣ 1 -agonists lose their ability to stimulate heart rate (22), which comes increasingly under ␤-adrenergic control, as seen in...

Patterned cardiomyocytes on microelectrode arrays as a functional, high information content drug screening platform

“…The neonatal rat cardiomyocyte culture was prepared using the cardiac isolation kit from Worthington[40]. All animal work was approved by the UCF IACUC and followed NIH guidelines.…”

Impaired cardiac energy metabolism in embryos lacking adrenergic stimulation

“…E10.5 and E11.5 mouse hearts were isolated under aseptic conditions and cultured in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum (Hyclone Laboratories) that had been charcoal-stripped to remove catecholamine and steroid hormones (41). The medium was additionally supplemented with penicillin G (100,000 U/l) and streptomycin (100 mg/l).…”

Autonomic cardiac innervation

“…Intrinsic cardiac adrenergic (ICA) cells may be the source of catecholamines, primarily epinephrine, in the developing rodent and human heart and contribute up to one-third of total cardiac epinephrine content 139 , 142 , 143 . The neonatal rat heart has functional α1 in addition to β adrenergic receptors, allowing broad responsiveness to epinephrine, particularly for α1-promotion of myocardial hypertrophy, with β1 adrenergic receptor control of heart rate increasing with postnatal age 139 , 144 , 145 . Although the fate of ICA cells is not certain, some may differentiate into pacemaker cells, however, a resident population is potentially the source of adrenergic support following transplantation 146 , 147 .…”