Effect of type-selective inhibitors on cyclic nucleotide phosphodiesterase activity and insulin secretion in the clonal insulin secreting cell line BRIN-BD11.

1. The cyclic nucleotide phosphodiesterases (PDEs) present in an insulin secreting cell line, BRIN - BD11, were characterized using calcium/calmodulin, IGF-1, isoenzyme-selective PDE inhibitors and RT - PCR. 2. Calmodulin activated cyclic AMP or cyclic GMP PDE activity in pellet and was 3 fold (P=0.002) more potent in activating cyclic nucleotide hydrolysis in pellet compared with supernatant fractions. 3. The PDE1/PDE5 inhibitor zaprinast inhibited both cyclic AMP and cyclic GMP PDE activity in both pellet and supernatant fractions of cell homogenates by a maximum of around 25% (IC(50) 1 - 5 microM), while rolipram (PDE4 selective) inhibited only cyclic AMP hydrolysis. 4. The PDE3-selective inhibitors Org 9935 (0.02 - 10 microM) and siguazodan (0.1 - 10 microM) inhibited cyclic AMP PDE activity in the pellet but not the supernatant fractions of cell homogenates, with a maximum inhibition of about 30%. IGF-1 (2 - 7.5 ng ml(-1)) potently augmented this PDE activity. 5. RT - PCR using specific primers for PDE3B, but not for PDE3A, amplified, from BRIN - BD11 cell total RNA, a 351 base pair product that was >97% homologous with rat adipose tissue PDE3B. 6. IBMX, Org 9935, siguazodan and rolipram (1 - 50 microM), but not zaprinast, each augmented glucose-induced insulin secretion in the presence of 16.7 mM but not 1 mM glucose. 7. These findings, in a clonal insulin secreting cell line, are consistent with an important role for PDE3B in regulating the pool of cyclic AMP relevant to the modulation of glucose-induced insulin secretion.