MODULATORS OF THE ADENYLATE-CYCLASE SYSTEM CAN ALTER ELECTROPHYSIOLOGICAL TASTE RESPONSES IN GERBIL

The adenylate cyclase system has been implicated in taste transduction . The purpose of this study was to determine whether application of mo dulators of the adenylate cyclase system to the tongue alter taste res ponses. Integrated chorda tympani (CT) recordings were made in gerbils to bitter, sweet, salty, sour, and glutamate tastants before and afte r a 4-min application of four types of modulators of the adenylate cyc lase system. The four types of modulators tested were: a) NaF, a compo und that promotes dissociation of GTP binding protein; b) forskolin, a powerful stimulant of adenylate cyclase; c) 8-bromoadenosine 3':5'-cy clic monophosphate sodium salt (8BrcAMP) and N-6,2'-O-dibutyryladenosi ne 3':5'-cyclic monophosphate sodium salt (DBcAMP), two membrane perme able forms of cAMP; and d) 1-(5-isoquinolinylsulfonyl)-2-methylpiperaz ine dihydrochloride (H-7) and N-(2-[methylamino]ethyl)-5-isoquinolines ulfonamide dihydrochloride) (H-8), which are protein kinase inhibitors . The taste compounds tested were: NaCl (30 mM), monosodium glutamate- MSG (50 mM), sucrose (30 mM), HCl (5 mM and 10 mM), KCl (300 mM), quin ine HCl (30 mM), MgCl2 (30 mM), erythromycin (0.7 mM and 1 mM), HCl (5 mM and 10 mM), and urea (2 M). The main findings were as follows. NaF (20 mM) significantly inhibited responses to bitter compounds up to 3 5% and enhanced the response to sucrose by 30%. NaCl (20 mM), used as a control for NaF, inhibited most responses up to 78% with no enhancem ent of sucrose as seen with NaF. 8BrcAMP (1.16 mM) reduced the respons es to bitter-tasting quinine HCl, MgCl2, and erythromycin but not to u rea. It also blocked the responses to KCl and HCl which have bitter co mponents. There was a slight enhancement of the sucrose response. It h ad no significant effect on NaCl or MSG. A similar trend was found for 5 mM DBcAMP. H-7 (300 mu M) slightly altered responses to several sti muli. These data indicate that modulation of the adenylate cyclase sys tem can affect the amplitude of neural responses of some bitter and sw eet taste responses.