Neuroregulation of Calcium Channel Function in Human Fetal Cardiac Myocyte Clusters

Abstract 114 Poster Session II, Sunday, 5/2 (poster 256)

Studies indicate that neuroregulation is important in the modulation of calcium channel function in the heart ( Legssyer et al., 1997 JMCC). We have previously shown that 1^st and 2^nd trimester human fetal hearts are dependent on calcium influx through the L-type calcium channels for contractions. However, we have not studied the regulatory role of neurohumoral agents on immature hearts. We studied the effect of isoproterenol, bethanechol, and nifedipine on contractions, in cardiac myocyte clusters from 1^st trimester human fetal hearts. Studies were performed under the guidelines of an approved institutional protocol (ETSU IRB#97-076e). Myocardium from 7-9 weeks gestation human fetal hearts were minced, digested and incubated in enriched culture medium at 37°. Spontaneously contracting myocardial clusters were selected for study. Studies were performed with the myocyte clusters bathed in normal Tyrode's solution, and paced at 0.25 Hz with platinum pacing electrodes. Contractions were measured using a video-edge detector. Contractions did not change from baseline after we perfused the myocyte clusters with 5, 10, 20 and 40 mM isoproterenol (7 clusters from 6 hearts), or bethanechol (n=5 clusters from 4 hearts). Contractions did not change after perfusing the myocyte clusters with 1 and 5 µM nifedipine, but decreased to 65% and 45% of baseline after perfusion with 10 and 20 µM nifedipine, respectively. Contractions after 10 or 20 µM nifedipine did not increase following subsequent administration of 20 or 40 mM isoproterenol. In summary, cardiac ventricular myocyte clusters from 1^st trimester human fetal hearts do not show a functional response to isoproterenol or bethanechol at concentrations up to 40 mM. Adrenergic modulation of calcium channel function is also not apparent.