A new approach to study the relationship between calcium waves and diastolic [Ca2+](i) in heart muscle cells

In the present study, changes in calcium waves with alternation of diastolic [Ca2+](i) were investigated in a single common rat neonatal cultured heart muscle cell without changes in extracellular conditions. Heart muscle cells were loaded with fluo-3 by the ''whole cell clamp'' technique. Rapid changes in diastolic [Ca2+](i) by variations in the membrane potential clarified the influences on calcium waves. When the membrane potential was held at 0 mV, inter wave basal [Ca2+](i) were maintained at a high level. The membrane-holding potential was then momentarily altered to -80 mV and the basal [Ca2+](i) registered a lower level within 1 sec. During these events, spontaneous calcium waves were analyzed by confocal laser scanning microscopy (X-t scanning mode). The frequency and velocity of calcium waves at 0 mV significantly increased compared with those at -80 mV. Moreover, these changes were more pronounced with increasing extracellular [Ca2+]. These results suggest that diastolic [Ca2+](i) directly influences calcium waves.