Table 2.

COX enzymes in healthy human skeletal muscle in relation to exercise and COX-inhibiting drugs

Isoform	Variant(s)	Comments
COX-1	Variant 1 (−1v1)	Relatively abundant at the transcript and protein level at rest and after acute and chronic exercise. The protein product commonly believed to interact with nonspecific COX-inhibiting drugs. Acute exercise increases transcript levels; chronic exercise training increases transcript and protein levels.
COX-1	Variant 2 (−1v2)	A truncated transcript of COX-1v1 (missing 111 bases from exon 9) that may not generate a functional protein product. Most abundant COX transcript but specific role in skeletal muscle unknown. Acute exercise and chronic exercise training increase transcript levels.
COX-1	Variant b (−1b)	Also known as COX-3. An intron-1-retaining version of COX-1 with 3 splice variants: −1b1, −1b2, −1b3. Apparently sensitive to common COX-inhibiting drugs in other tissues. Nondetectable or very low transcript levels at rest and nonresponsive to acute and chronic exercise. Unlikely involved in exercise adaptations or related COX-inhibitor effects.
COX-2		Very low or nondetectable transcript and enzymatically active protein levels at rest and after acute and chronic exercise. Although low, transcript levels increase with ingestion or infusion of COX-2-specific or nonspecific COX inhibitors after acute exercise, as well as with chronic exercise training.

See text and related studies (18, 69, 105, 116, 125, 138) for further discussion of skeletal muscle COX.