The Sensex at the Bombay Stock Exchange opened with a good gain of 187 points, or 1.1 percent, at 17,246, on Friday morning. But later the Sensex gave up all its initial gains, and stood 220 points, or 1.3 percent in negative territory, to slip below the 17,000 level, at 16,840 on profit-booking by investors, in afternoon deals, a short while ago.Other Asian markets in Hong Kong, China, Singapore, South Korea, Japan and Taiwan were trading mixed, today. But Wall Street's Dow Jones Industrial Average had surged 3.9 percent, overnight, after data showed a drop in weekly jobless claims in the world's biggest economy.