San Diego-based Slacker, the online radio streaming service, is in a major expansion of its content today, as public radio broadcaster American Public Media said it launched a number of new, interactive stations on Slacker. The broadcaster--which publishes Marketplace and The Current, two popular public radio programs--said its programming will be available for free on the Slacker service. Public radio listeners are likely familiar with American Public Media via its programs Marketplace with Kai Ryssdal, Marketplace Morning Report, Marketplace Tech Report and Marketplace Money.The Current is a non-commercial, music station.