The inducible alkaline phosphatase of rat heart. Some properties of the enzyme and factors influencing its activity

Subcutaneous injection of isoprenaline into rats produces a rapid rise in alkaline phosphatase activity which is largely confined to the right atrium of the heart. The phosphatase activity of extracts of atrial tissue from treated animals is on average four times that of controls. The rise in activity is largely suppressed by previously treating the animals with cycloheximide or actinomycin D. Comparison of the properties of the alkaline phosphatase in extracts of atria from isoprenaline-treated rats with control preparations shows the stimulated enzyme activity to be similar to that present in the resting state. In a number of respects, including substrate specificity, response to activators and inhibitors, rate of loss of activity on heating and electrophoretic mobility of the native and modified enzyme, the atrial phosphatase resembles alkaline phosphatases from other mammalian non-intestinal and non-placental tissues. These results suggest that the effect of isoprenaline is to increase the rate of synthesis of atrial alkaline phosphatase, and the ability of the tissues of the right atrium to respond in this way may be related to the rich sympathetic innervation of this part of the heart.