Expression of cannabinoid receptor 1 (CB1) (a) and cannabinoid receptor 2 (CB2) (b) receptor protein in synovial tissue of patients with osteoarthritis (OA) (lanes 2 to 5) or rheumatoid arthritis (RA) (lanes 6 to 8) detected by Western blotting and quantified by densitometry. CHO-K1 cells recombinantly expressing either CB1 or CB2 receptor were used as a positive control (lane 1). Receptor expression was calculated as a percentage of expression of the internal control, β-actin. Data are presented as mean ± standard error of the mean of the expression of CB1 and CB2 protein in four OA and four RA patients, assessed in three separate experiments. Expression of CB1 (c) and CB2 (d) receptor RNA in fibroblast-like synovial cells derived from tissue of patients with OA or RA detected by 'touchdown' polymerase chain reaction. A human neuroblastoma cell line (SH-SY5Y) endogenously expressing CB1 cannabinoid receptor and CHO-K1 cells recombinantly expressing CB2 receptor were used as positive controls, respectively. bp, base pairs.