Ambulance Firm Merger: CareLine Inc. stockholders are scheduled to meet Thursday to vote on the Santa Ana-based ambulance service company's proposed merger with Laidlaw Inc., a Canadian transportation and waste management company. A year ago, CareLine launched a search for a financial partner to help fund acquisitions of ambulance firms nationwide, according to the company's prospectus for the merger. The company had already wracked up $170 million in debt and needed fresh capital to avoid curtailing its acquisitions. Company executives first explored a merger with Laidlaw officials in October last year but didn't reach an agreement. Later, as a possible alternative source of funding, CareLine officials tried negotiating with a private investor for a $25-million sale of preferred stock, but they deemed the terms unfavorable to existing shareholders. In May, they turned to American Medical Response Inc., a Boston-based ambulance firm, but merger talks bogged down over AMR's concerns about CareLine's $2.2-million loss for the second quarter and other issues. Meanwhile, CareLine and Laidlaw executives resumed discussions and finally struck a deal in which Laidlaw would pay $180 million in common stock for CareLine. Stockholders of CareLine would receive 1.1 shares of non-voting Laidlaw stock for each CareLine share. The meeting will be held at 2 p.m. at Sutton Place Hotel, 4500 MacArthur Blvd., Newport Beach.