Rodent β-cell lines endogenously express GHR, JAK2, and IGF-IR and are responsive to GH and IGF-I. A, Comparison of expression levels of GHR, JAK2, and IGF-IR among MIN6, BTC6, and INS-1 cells by immunoblotting with anti-GHR, anti-JAK2, and anti-IGF-IR antibodies, respectively. WB, Western blot. B and C, Serum-starved cells were stimulated with vehicle (−), bGH (500 ng/ml), or IGF-I (20 ng/ml) for 15 min. Cell extracts were analyzed by immunoblotting with anti-pSTAT5, anti-pAkt, or anti-β-actin (loading), as indicated.