Table 2.

Differential effect of insulin and glucose on activities of adenosine-metabolizing enzymes in cultured rat cardiac fibroblasts

	5 mm glucose, 10 nm insulin	5 mm glucose, no insulin	25 mm glucose, 10 nm insulin	25 mm glucose, no insulin
SAH hydrolase
Cytoplasm	0.061 ± 0.017	0.076 ± 0.021	0.068 ± 0.017	0.084 ± 0.025
Membranes	ND	ND	ND	ND
5′-Nucleotidase
Cytoplasm	3.18 ± 0.42	3.16 ± 0.38	3.11 ± 0.41	3.07 ± 0.49
Membranes	39.87 ± 4.12	37.38 ± 3.66	40.13 ± 4.84	33.91 ± 3.32
AMP deaminase
Cytoplasm	1.65 ± 0.28	1.74 ± 0.32	2.81 ± 0.43*§	2.98 ± 0.51*§
Membranes	ND	ND	ND	ND
Adenosine deaminase
Cytoplasm	9.31 ± 1.25	8.21 ± 1.31	3.32 ± 0.61*§	2.94 ± 0.53*§
Membranes	0.20 ± 0.03	0.60 ± 0.09*	0.18 ± 0.03§	0.58 ± 0.07*†
Adenosine kinase
Cytoplasm	0.57 ± 0.16	0.63 ± 0.14	0.49 ± 0.17	0.53 ± 0.15
Membranes	ND	ND	ND	ND

The data show enzyme activity (nmol min⁻¹ mg⁻¹). At ∼70% confluence, the culture medium was changed to Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, glucose and insulin at concentrations as indicated. No insulin refers to a concentration of 10⁻¹¹m. On the third day of culture, cells (1.5 × 10⁷) were harvested and enzymes activities in cytosolic and membrane fraction were determined. The data represent the mean ± s.d. from four independent experiments.

^*P < 0.05 versus 5 mm glucose, 10 nm insulin

^§P < 0.05 versus 5 mm glucose, no insulin

^†P < 0.05 versus 25 mm glucose, 10 nm insulin. ND, not determined.