TOKYO — Mobile communication powerhouse Index Holdings will sell its 71% stake in Nikkatsu, Japan’s oldest studio, by the end of February.Index has already inked to sell 34%, worth 2.4 billion yen ($27 million), to Nippon Television Network and is negotiating to transfer the remainder to four or five unnamed companies. Index aims to cut its interest-bearing debt, while NTV, which is already engaged in pic investment and production, will gain a production subidiary. As ad revenues fall in their core broadcasting biz, Japanese TV networks see pics as a lucrative source of income. Founded in 1912, Nikkatsu is a producer, distributor and operator of six theaters. It has a studio in Tokyo. It also manages a library, including its Nikkatsu Action pics from the 1950s to 1970s and Nikkatsu Roman Porno pics from the 1970s to 1980s. It became an Index subsidary in 2005.