EVIDENCE FOR PRESENCE OF CA2+ CHANNEL-GATED CA2+ STORES IN NEONATAL HUMAN ATRIAL MYOCYTES

The characteristics of Ca2+ signaling in fura 2-loaded whole cell-clamped myocytes obtained from samples of human atrial appendages of 3-day to 4-yr-old patients were examined. In isolated myocytes, activation of Ca2+ current (I-Ca) (2.47 +/- 0.23 pA/pF) at 0 mV elicited sizable intracellular Ca2+ (Ca-i) transients (240 +/- 45 nM), which were caused by the release of Ca2+ from intracellular stores as they were suppressed in the presence of ryanodine or caffeine. The voltage dependence of both Ca-i transients and I-Ca were similar and bell shaped. The rate of release of Ca2+, normalized for the maximal Ca2+ release, increased with age, indicating increased efficiency of Ca2+ signaling in more mature myocytes. The results suggest that I-Ca-gated release of Ca2+ from the sarcoplasmic reticulum is the primary mechanism regulating the signaling of contraction in early postnatal as well as older human atrial myocytes.