Chronotropic responsiveness of developing sinoatrial and ventricular rat myocytes to autonomic agonists following adrenergic and cholinergic innervation in vitro.

Abstract

The chronotropic responses of isolated sinoatrial node and ventricular muscle cells to neurotransmitters were compared in vitro with and without selective adrenergic and cholinergic innervation. Explants of either thoracolumbar sympathetic ganglion or sacrococcygeal spinal cord were added to cultures of newborn rat sinus node regions or ventricular apexes harvested before the onset of autonomic innervation in vivo. Catecholamine synthesis was detected by glyoxylic acid histofluorescence. Acetylchoiine synthesis was indicated by monoclonal antibody labeling of choline acetyltransferase. After electrical or pharmacological stimulation of neurons, the chronotropic response of individual myocardial cells confirmed the presence of neuroeffector transmission; the nature of the myocyte response identified the stimulated neuron as either adrenergic or cholinergic. Chronotropic responses of all myocardial cells to norepinephrine or acetylchoiine were transcribed on a recorder coupled to a video photoconductive cell monitor. Isolated sinoatrial node cells were supersensitive to norepinephrine and acetylchoiine; thresholds were 3xlO' 16 M and 6xlO~1 5 M, respectively. These sinoatrial node cells remained sensitive to both norepinephrine and acetylchoiine after the development of innervation in vitro. Ventricular cells also were sensitive with thresholds of 3x10"" M and 6xlO" 14 M to norepinephrine and acetylchoiine, respectively. However, following in vitro innervation, ventricular cells were significantly less sensitive to norepinephrine and acetylchoiine (thresholds 3xlO~ M and 6 x 1 0 " M). These data are the first to demonstrate that neurotrophic modulation is not homogeneous throughout the myocardium and that it may be dependent on the specific myocardial cell innervated. (Circulation Research 1989;64:1051-1062

Direct contact between sympathetic neurons and rat cardiac myocytes in vitro increases expression of functional calcium channels.

“…The model system for the in vitro innervation experiments deserves comment (2,7,16). Ventricular myocytes were cultured from l-d postnatal rat hearts.…”

“…In the intact ventricle, myocytes comprise a numerical minority ofcells, so that ligand binding studies or physiologic studies reflect the responses of neural, vascular, and connective tissue elements as well as ventricular myocytes. In vitro sympathetic innervation models have been reported by several laboratories (7,16,19). A particular advantage of our approach using relatively large ganglia rather than finely minced neural tissue in culture is that it permits the examination of denervation in vitro by allowing removal or degradation of virtually all neural tissue (2).…”

“…Cultures were prepared by a modification ofthe method ofAtkins and Marvin (7) and by a modification ofthe method of Barnett and Galper (2). After sacrifice of l-d-old neonatal rats, supracervical sympathetic ganglia were removed aseptically and placed in culture dishes that contained Hanks' salt solution.…”

A soluble neuronal factor alters contractile function of ventricular myocytes without effect on troponin T isoform expression

“…Since the onset of Sympathetic innervation in vitro has been shown to sympathetic neurotransmission is an early postnatal event, affect neonatal cardiac myocyte growth [1,2], chronotropic understanding the response of the heart to sympathetic response [3] and contractility [4]. These developmental innervation is important to understanding normal developresponses can be demonstrated in a myocyte neuron coment and in understanding the response of the neonatal culture system in which the myocytes are functionally myocardium to adrenergic agonists if required to maintain innervated.…”

“…These effects of PC12 conditioned medium and innervation were not suppressed by adrenergic or muscarinic antagonists nor reproduced by neuropeptide Y or somatostatin. Neuronal PC12 conditioned medium but not chromaffin PC12 conditioned medium, increased metabolic activity of the myocytes as detected by 3 [ H]-2-deoxyglucose, indicating that the effect was specific to the neuronal PC12 cells. The in vitro switch of troponin T isoform expression was not altered by exposure to PC12 conditioned medium.…”