Activation of epithelial sodium channels by prostasin in Xenopus oocytes

Prostasin, a novel serine protease, was purified from seminar fluid, and it s cDNA sequence was determined. Expression of prostasin was detected in hum an tissues, including prostate, kidney, and lung, as well as bodily fluids, including seminal fluid and urine. However, its physiologic role in the hu man body is not known. Recently, a novel regulatory mechanism by which seri ne proteases activate epithelial sodium channel in the Xenopus oocyte was i dentified. Therefore, it was hypothesized that prostasin could activate sod ium currents, and a rat prostasin cDNA clone was isolated to investigate it s physiologic function. Rat prostasin mRNA is expressed predominantly in ki dney, and lower levels of expression were detected in prostate, lung, colon , stomach and skin. These all are epithelial tissues in which the epithelia l sodium channel (ENaC) is expressed. Coexpression of rat prostasin and rat ENaC in Xenopus oocytes increased the amiloride-sensitive sodium current b y twofold. Preincubation of oocytes that express-ed prostasin with aprotini n did not result in an increase in sodium current, compared with the contro l. The removal of aprotinin from the bath solution resulted in a twofold in crease of the current only in oocytes that expressed prostasin, which indic ates that protease activity of prostasin is required for the ENaC activatio n. Expression of rat prostasin had no effect on the potassium current when expressed with rat renal outer medulla K channel, which shows specificity o f prostasin action for ENaC. These results indicate that prostasin acts as an extracellular regulator of ENaC.