The presence and regulation of a hormone-sensitive cyclic GMP-inhibited cyclic nucleotide phosphodiesterase (cGI PDE) in rat brown adipose cells was investigated. cDNA clones for two cGI PDE isoforms, cGIP1 and cGIP2, have been isolated. Using a rat cGIP1 (RcGIP1) cDNA probe, RcGIP1 mRNA (∼5.3 kb) was detected in Northern blots of both brown and white adipose RNA. cGI PDE was detected in both microsomal and plasma membrane fractions of brown and white adipose cells by Western blotting using anti-RcGIP1 peptide antibody. When cells were incubated with insulin before membrane preparation, cGI PDE activity in the microsomal fraction was increased by 2- to 2.5-fold within 10 min. Isoproterenol also stimulated the activity of cGI PDE in the microsomal fraction by 1.5-fold. In cells incubated with both insulin and isoproterenol, microsomal cGI PDE activity was similar to that in microsomal fractions isolated from cells incubated with insulin alone. These results suggest that the hormonal regulation of cGI PDE, presumably a cGIP1 isoform, in rat brown adipose cells is similar to that in white adipose cells.
