Luminent Mortgage Capital ( LUM) plunged for the second time in a week after the struggling lender got notices of default from two lenders. The San Francisco-based mortgage company said in a statement that it "is continuing to vigorously explore all of its alternatives with respect to its sudden liquidity issues resulting from the unanticipated and extraordinary disruptions in the secondary mortgage and national real estate markets." Luminent has been hard hit by margin calls from lenders requesting additional collateral. The company's shares dropped 31 cents to 77 cents Wednesday, two days after they dropped three-quarters of their value in a single day. That plunge came after the company suspended its dividend. Luminent had said just a week earlier that its quarterly dividend payment of 32 cents a share was "secure" and "will not be canceled." The default comes just days after the collapse of another lender, American Home Mortgage ( AHM) of Melville, N.Y., which filed for Chapter 11 bankruptcy protection after being hit by the collapse of the market for mortgage securities.