Statistics.
Statistical analysis was performed with SPSS 20.0 computer software (SPSS Inc., Chicago, IL, USA). To compare the quantitative variables, the Student’s t-test was used. Cytosolic Ca 2+ was analyzed using a one-way analysis of variance followed by multiple Tukey-Kramer comparisons. Data are expressed as the mean and the standard deviation. A p level lower than 0.05 was used to indicate a significant difference.