Abstract
The relation between spontaneous contraction, Ca 2+ oscillations, and sarcoplasmic reticulum (SR) function was studied in cultured neonatal rat cardiac myocytes. Spontaneous contraction and Ca 2+ oscillations were irregular at day 2 of culture but became regular at day 6 of culture in neonatal rat cardiac myocytes. The rate of spontaneous contraction and the frequency of Ca 2+ oscillations were decreased by verapamil and were abolished in the absence of extracellular Ca 2+ at both day 2 and day 6 of culture. Ryanodine and thapsigargin increased the rate of contraction and the frequency of Ca 2+ oscillations at day 2 of culture but did not affect contractions and Ca 2+ oscillations at day 6 of culture. Ultrastructural observation showed that the structure of SR developed less at day 6 of culture. The present results suggest that spontaneous contraction and Ca 2+ oscillations are due mainly to extracellular Ca 2+ influx but not to Ca 2+ release from SR in neonatal rat cardiac myocytes.
Published Version
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