The significance of inhibitor-resistant alkaline phosphatase in the cytochemical demonstration of transport adenosine triphosphatase.

The hydrolysis of disodium p-nitrophenyl phosphate at pH 9.0 by slices of formaldehydee-fixed rat renal cortex was investigated by colorimetric estimation of the nitrophenol liberated. It was found that three types of activity could be identified on the basis of their responses to inhibitors and cations: (a) alkaline phosphatase sensitive to inhibition by L-tetramisole; (b) potassium-dependent phosphatase, probably identifiable with the phosphatase component of sodium-potassium-dependent transport adenosine triphosphatase (?Na-K-ATPase); and (c) alkaline phosphatase insensitive to L-tetramisole. It was found that in the presence of strontium ions, as used in Na-K-ATPase cytochemistry, the activities of the second and third types of enzyme were approximately equal. The implications of these findings for the cytochemical demonstration of Na-K-ATPase are discussed.