Shares of healthcare-related companies sank after Amazon.com , Berkshire Hathaway and JPMorgan said they plan to form a venture aimed at lowering healthcare costs for their U.S. employees. Health insurer UnitedHealth’s 3.2 percent drop was the most on the Dow, while Express Scripts’ 6.2 percent decline weighed the most on the Nasdaq and S&P. “Investors are getting a bit worried about inflation which has led some people to believe that the Fed might be more aggressive when it comes to raising rates,” said Robert Pavlik, chief investment strategist at SlateStone Wealth.