Table I.

Potassium oxalate and potassium phosphate stimulated Ca²⁺/H⁺-antiport but not Ca²⁺-pump activity

Potassium Salt	Net Ca2+ Uptake
	Total	Pump	Antiport
	nmol/mg (-fold)
None	1.92  (1.00)	0.98  (1.00)	0.94  (1.00)
+Potassium oxalate	5.00  (2.63)	1.04  (1.06)	3.96  (4.21)
+Potassium phosphate	3.95  (2.06)	0.90  (0.92)	3.05  (3.25)

Net ATP-dependent ⁴⁵Ca²⁺ uptake at 6 min was determined with 0.1 μm Ca in the reaction mixture as described in Figure 5. Uptake was measured in the absence (Total) or presence (Pump) of 5 μm gramicidin and 0.5 μm bafilomycin. Antiport activity was determined as the difference between “total” and “pump” activity. Potassium oxalate or potassium phosphate was added to a final concentration of 10 mM. Data represent the averages of two experiments.