Inhibition of adenosine triphosphatase (ATPase) by silver nitrate (AgNO3) in vitro was studied in microsomal fractions or tissue homogenates of canine brain and kidney and human kidney. In microsomal fractions, AgNO3 was an indiscriminate inhibitor of ouabain-sensitive (Na+ + K+ ATPase) and ouabain-insensitive (Mg2+ ATPase) activities, with 50% inhibition obtaining at concentrations on the order of 10–7 to 10–6 M. Changing the concentrations of Na+, K+, H+, Mg2+, and ATP did not alter the fractional inhibition of Na+ + K+ ATPase by a constant concentration of AgNO3. An aqueous suspension of silver sulfadiazine had an inhibitory potency similar to AgNO3. It was concluded that silver gives a different pattern of Na+ + K+ ATPase inhibition than other metallic inhibitors of the enzyme so far examined.
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