Cell culture modifies Ca2+ signaling during excitation–contraction coupling in neonate cardiac myocytes

In heart, the excitation–contraction coupling (ECC) mechanism changes during development. Primary cell culture has been used to study Ca2+ signaling in newborn (NB) rat heart. In this work, the effects of cell culture on the action potential (AP) and ECC Ca2+ signaling during development were investigated. Specifically, AP, Ca2+ currents (ICa), and ryanodine receptor (RyR) properties (i.e. density, distribution, and contribution to Ca2+ transients and Ca2+ sparks) were defined in cultured myocytes (CM) from 0-day-old NB rat at different times in culture (1–4 days). Compared with acutely dissociated myocytes (ADM) from NB of equivalent ages (1–4 days), CM showed lower RyR density (50% at 1 day, 25% at 4 days), but larger RyR contribution to the Ca2+ transient (25% at 1 day, 57% at 4 days). Additionally, Ca2+ sparks were larger, longer, wider, and more frequent in CM than in ADM. RyR cellular distribution also showed different arrangement. While in CM, RyRs were located peripherally, in ADM of equivalent ages a sarcomeric arrangement was predominant. Finally, CM showed a two-fold increase in sarcolemmal Ca2+ entry during the AP. These results indicated that primary culture is a feasible model to study Ca2+ signaling in heart; however, it does not precisely reproduce what occurs in ECC during development.