ABSTRACT: Phosphodiesterase type 4 (PDE4) inhibitors prevent hydrolysis of cyclic adenosine monophosphate and increase protein kinase A (PKA)-mediated phosphorylation. PDE4 inhibitors also regulate responses to ethanol and GABAergic drugs. We investigated mechanisms by which the PDE4 inhibitor, apremilast, regulates acute effects of ethanol and GABAergic drugs in male and female mice. Apremilast prolonged the sedative-hypnotic effects of gaboxadol, zolpidem, and propofol but did not alter etomidate effects, and unexpectedly shortened the sedative-hypnotic effects of diazepam. Apremilast prolonged rotarod ataxia induced by zolpidem, propofol, and loreclezole, shortened recovery from diazepam, but had no effect on ataxia induced by gaboxadol or etomidate. The PKA inhibitor H-89 blocked apremilast's ability to prolong the sedative-hypnotic effects of ethanol, gaboxadol, and propofol and to prolong ethanol- and propofol-induced ataxia. H-89 also blocked apremilast's ability to shorten the sedative-hypnotic and ataxic effects of diazepam. The β1-specific antagonist, salicylidene salicylhydrazide (SCS), produced faster recovery from ethanol- and diazepam-induced ataxia, but did not alter propofol- or etomidate-induced ataxia. SCS shortened the sedative-hypnotic effects of ethanol and diazepam but not of propofol. In Xenopus oocytes, a phosphomimetic (aspartate) mutation at the PKA phosphorylation site in β1 subunits decreased the maximal GABA current in receptors containing α1 or α3, but not α2 subunits. In contrast, phosphomimetic mutations at PKA sites in β3 subunits increased the maximal GABA current in receptors containing α1 or α2, but not α3 subunits. The GABA potency and allosteric modulation by ethanol, propofol, etomidate, zolpidem, flunitrazepam, or diazepam were not altered by these mutations. We propose a model whereby apremilast increases PKA-mediated phosphorylation of β1-and β3-containing GABAA receptors and selectively alters acute tolerance to ethanol and GABAergic drugs.
