Table 1.

Parameters for the two-exponential fit to the data for cardiac muscle

Incubation	Chase	N	P1	T1 (s)	P2	T2 (s)
mantATP	ATP	64	0.66 ± 0.01	14 ± 1	0.27 ± 0.01	144 ± 10
ATP	mantATP	9	0.63 ± 0.03	12 ± 1	0.29 ± 0.02	138 ± 21
mantADP	ADP	15	0.83 ± 0.01	10 ± 1	0.09 ± 0.01	261 ± 49
ADP∗	mantATP	17	0.92 ± 0.02	9 ± 1	0.04 ± 0.02	75 ± 16
mantATP +ATP†	ATP	8	0.51 ± 0.06	17 ± 4	0.08 ± 0.01	123 ± 12
mantATP	ADP	17	0.74 ± 0.02	12 ± 1	0.19 ± 0.02	76 ± 10
mantATP	ATP/Ca	22	0.64 ± 0.04	26 ± 2	0.26 ± 0.02	228 ± 22

First two columns give the nucleotides in the initial incubation and the chase solutions. The third column gives number of experiments averaged. P₁ and P₂ are the magnitudes and T₁ and T₂ are the time constants for the first and second phases of the two-exponential function that was fit to the data (see Materials and Methods). Errors are standard errors of the mean.

^∗Similar results were obtained in ADP or in rigor (in the absence of nucleotides), or when the nucleotide in the chase was 250 μM mantADP, and these results are included in this analysis.

^†The data were normalized to the cell fluorescence in the absence of competition with ATP.