Table 5.

Percentage decreases in the rates of XB detachment and recruitment in WT and KO preparations following incubation with OM at different levels of activator [Ca²⁺].

pCa	WT		KO
	krel (% decrease)	kdf (% decrease)	krel (% decrease)	kdf (% decrease)
6.2	66.5±3.8	55.7±3.5	63.2±3.0	40.2±4.5*
6.1	57.9±2.4	30.2±5.7	76.4±3.0*	30.1±3.0
6.0	50.8±1.6	26.3±4.8	61.7±2.7*	27.3±2.7
5.9	41.8±2.3	18.6±3.3	60.9±1.9*	24.3±3.7

k_rel: rate of XB detachment; k_df: rate of XB recruitment. Values are expressed as mean ± S.E.M. Paired t-tests were used to compare the data between pre- and post-OM treatment groups. 12–16 preparations were analyzed from 5 hearts and 13–18 preparations were analyzed from 7 hearts for WT and KO groups, respectively with multiple preparations from each heart. The decrease in k_rel was less pronounced as the level of activator [Ca²⁺] increased in the WT group but such a trend was absent in the KO group. The slowing in k_df was progressively decreased as the level of activator [Ca²⁺] increased in both the WT and KO groups. Furthermore, the % decreases in k_rel in the KO group were more pronounced than WT at pCa’s 6.1, 6.0, and 5.9. The % decreases in k_df in the WT group were significantly higher than KO at pCa 6.2. Correlation analysis showed a strong positive correlation between pCa vs. % decreases in k_rel and k_df in the WT group (correlation coefficient values of 0.99 and 0.93, respectively). In the KO group, there was a strong positive correlation between pCa vs. % decreases for k_df (correlation coefficient value of 0.94), and a moderate positive correlation for pCa vs. % decreases in k_rel in the KO group (correlation coefficient value of 0.38). This is due to the fact that the % decreases in k_rel in the KO group are less sensitive to increases in submaximal [Ca²⁺]. Independent t-tests were used to test the differences between WT and KO groups at each pCa.

^*Significantly different from the corresponding WT group; P < 0.05.