A possible role for protein kinase C in the regulatory differences between intra-abdominal and subcutaneous human...

1. The adenosine A1-receptor agonist N6-(phenylisopropyl)adenosine inhibited lipolysis in a dose-dependent manner in human adipocytes. The effect is mediated by the inhibitory guanine-nucleotide-binding protein(s) that can be phosphorylated and thereby inactivated by protein kinase C. 2. Stimulation of protein kinase C by 12-O-tetradecanoyl-phorbol-13-acetate attenuated the inhibitory effect of the adenosine agonist. 3. Omental fat cells are less sensitive to adenosine than subcutaneous cells, although the stimulatory arm of cyclase regulation appears normal. Protein kinase C activity was measured in the soluble and particulate fractions of human omental and subcutaneous adipose tissue. Omental adipose tissue had a twofold higher membrane-bound and a threefold higher soluble protein kinase C activity. 4. It is therefore possible that the differences in regulation between the two sites are caused by different C kinase activities, causing variable phosphorylation of the inhibitory guanine-nucleotide-binding protein(s).