Effect of type-selective inhibitors on cyclic nucleotide phosphodiesteraseactivity and insulin secretion in the clonal insulin secreting cell Line BRIN-BD11

1 The cyclic nucleotide phosphodiesterases (PDEs) present in an insulin sec reting cell line, BRIN-BD11, were characterized using calcium/calmodulin, I GF-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 hydrolysi s in pellet compared with supernatant fractions. 3 The PDE1/PDE5 inhibitor zaprinast inhibited both cyclic AMP and cyclic GM P PDE activity in both pellet and supernatant fractions of cell homogenates by a maximum of around 25% (IC50 1-5 mu M), while rolipram (PDE4 selective ) inhibited only cyclic AMP hydrolysis. 4 The PDE3-selective inhibitors Org 9935 (0.02-10 mu M) and siguazodan (0.1 -10 mu M) inhibited cyclic AMP PDE activity in the: pellet but not the supe rnatant fractions of cell homogenates, with a maximum inhibition of about 3 0%. IGF-1 (2-7.5 ng ml(-1)) potently augmented this PDE activity. 5 RT-PCR using specific primers for PDE3B, but nor for PDE3A, amplified, Fr om BRIN-BD11 cell total RNA, a 351 base pair product that was >97% homologo us with rat adipose tissue PDE3B. 6 IBMX, Org 9935, siguazodan and rolipram (1-50 mu M), but not zaprinast, e ach 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 w ith an important role for PDE3B in regulating the pool of cyclic AMP releva nt to the modulation of glucose-induced insulin secretion.