Table 1.

Calibration of the ATP measurements

Solution	Osmolality mosmol (kg H2O)−1	Counts per pmol ATP (s−1)
Cl−1	260	568
	200	586
	170	693
	155	708
	140	724
SO42−	260	958
	140	1265

Calibration was performed as shown in Fig. 2B in solutions with osmolalities indicated in the second column. These calibration factors were used to calculate Q_ATP from the photon counts recorded during experiments as illustrated in Fig. 4.