Nuclear calcium oscillation in cultured neonatal rat myocytes

AIM: To determine whether nuclear Ca²⁺ is independently regulated from the cytosolic Ca²⁺ and nuclear Ca²⁺ oscillation induced by many modulating factors in cultured rat neonatal myocytes and its mechanism. METHODS: Rat neonatal cardiac myocytes were cultured, and fluo-4/AM was loaded as calcium probe. The changes of cytosolic and nuclear Ca²⁺ were observed by confocal laser microscopy. RESULTS: Calcium fluorescent intensity oscillated slightly in myocardiocytes and the average intensity was much higher in the nucleus than that in the cytosole. Ca²⁺ oscillation in nucleus and cytosole induced by norepinephrine, isoproperenol, ATP were completely blocked by Ca²⁺-ATPase antagonist thapsigargin (10^-6 mol/L),L-type Ca²⁺ channel blocker verapermil (500 μmol/L) and KCl (20 mmol/L). Ca²⁺-ATPase antagonist thapsigargin completely blocked the propagation of Ca²⁺ waves and simutaneouly induced a temporary Ca²⁺ increase followed by a magnificient drop and loss of response to norepinephrine. CONCLUSIONS: The results suggested that generation and maintenance of calcium oscillation both in cytosole and nucleus depended on extracellular Ca²⁺ influx, membrane potential, Ca²⁺ release and uptake of cytosolic and nuclear calcium stores. The difference between cytosolic calcium and nuclear calcium indicated that calcium regulating system relatively independent of cytosole may exist in nucleus.