Developmental changes in cardiac myocyte calcium regulation.

Developmental changes in the contributions of transsarcolemmal Ca2+ influx and Ca2+ release from intracellular storage sites to myocardial contraction were evaluated in isolated ventricular myocytes from neonatal (aged 1-7 days) and adult (aged 8-10 weeks) New Zealand White rabbits. Contractions ceased in one beat when extracellular Ca2+ was decreased from 1mM to micromolar levels using a rapid perfusion technique. On reperfusion with 1 mM Ca2+, recovery of control contraction amplitude occurred after significantly fewer beats in neonatal myocytes compared with adult myocytes, and after 1 minute compared with 5 minutes of reduced Ca2+. After 15 minutes of perfusion with either 1 or 10 microM ryanodine, contraction amplitude decreased in both age groups, but the decrease was significantly greater in adults than in neonates. These experiments indicate that isolated ventricular myocytes may be used in the study of developmental changes in intracellular Ca2+ regulation. Results suggest that cardiac contraction in neonates is relatively more dependent on transsarcolemmal Ca2+ influx. Furthermore, although Ca2+ release from intracellular storage sites is present in both neonates and adults, its role in cardiac contraction is more significant in adults.