Forskolin and 3-isobutyl-1-methylxanthine increase basal and sodium nitroprusside-elevated cyclic GMP levels in adult guinea-pig cerebellar slices.

In this study, the interaction between 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in [3H]adenine- or [3H]-guanine-prelabelled adult guinea-pig cerebellar slices was investigated. Basal levels of [3H]cGMP were enhanced by forskolin, although no plateau was reached over the concentration range tested (0.1-100 microM). However, forskolin elicited a concentration-dependent, saturable potentiation of sodium nitroprusside (SNP)-stimulated [3H]cGMP accumulation (forskolin EC50 value of 0.98 +/- 0.23 microM; 10 microM forskolin produced a 1.8 +/- 0.3-fold potentiation of the SNP response at 2.5 min). The forskolin potentiation was observed at all concentrations of SNP tested (0.001-10 mM). Forskolin also elicited a large stimulation of [3H]-cAMP in [3H]adenine-prelabelled guinea-pig cerebellar slices; however, 1,9-dideoxyforskolin failed to elicit either a [3H]cAMP response or a potentiation of the SNP-induced [3H]cGMP response at concentrations up to 100 microM. Pretreatment with oxyhaemoglobin (50 microM) inhibited the response to SNP (1 mM) and forskolin (10 microM), as well as the response evoked by the combination of SNP and forskolin. NG-Nitro-L-arginine (100 microM) inhibited the response to forskolin alone, but did not change the response to SNP or the potentiation induced by forskolin on SNP-induced [3H]cGMP levels. The protein kinase inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7; 100 microM), staurosporine (10 microM), polymyxin B (100 microM), and Ro 31-8220 (10 microM) had no effect on the [3H]cGMP response to either SNP or the combination of SNP plus forskolin. N6,2'-Dibutyryl cAMP, at concentrations up to 10 mM, was also without effect on [3H]cGMP levels induced by SNP.(ABSTRACT TRUNCATED AT 250 WORDS)