Mikolas, 25, was acquired by Pittsburgh from San Diego on November 25 with OF Jeff Decker in exchange for 1B Alex Dickerson. He had been designated for assignment by the Padres on November 20.
The right-hander spent most of 2013 at Triple-A Tucson, going 4-2 with a 3.25 ERA in 54 games and ranking third in the Pacific Coast League with 26 saves. Mikolas had four brief stints with San Diego (June 23-24; July 9-12; July 21-22; July 30-31) and pitched 1.2 scoreless innings in two total appearances, July 11 vs. San Francisco (1.0 IP) and July 31 vs. Cincinnati (0.2 IP).
Mikolas made his major league debut with the Padres in 2012 with a 2-1 record and 3.62 ERA (13 ER/32.1 IP) in 25 games. He appeared in his first major league game on May 5 and had three overall stints with San Diego, spending the final two months of the season with the club.
Selected by San Diego in the seventh round of the 2009 First Year Player Draft, Mikolas has pitched exclusively in relief in his last four pro seasons and has 64 minor league saves.
McGuiness was designated for assignment on December 27 when outfielder Shin-Soo Choo was added to the major league roster. He saw his first major league action with Texas last season, batting .176 (6-34) with one double and one RBI in 10 games. He spent the rest of the year with Triple-A Round Rock, batting .246 with 11 home runs, and 63 RBI in 104 games with the Express.
Ortega was received on a waiver claim from Colorado on November 27. He batted .228 with one homer, 10 RBI, and 9 stolen bases in 42 games for Double-A Tulsa of the Texas League in 2013. The left-handed batter was the Drillers leadoff hitter and centerfielder before sustaining a hairline fracture of his shin on June 20 and missing the remainder of the season. The Rangers have 10 days to trade, release, or outright Ortega to the minor leagues.
With today's transactions, the Rangers still have a full 40-man roster.