G‐protein coupled activation of potassium channels by endogenous neuropeptides in snail neurons

Abstract

Members of the mytilus inhibitory peptide (MIP) family play an important role in the modulation of many physiological processes in molluscs. The signal transduction pathways affected by the MIP effect have not, however, been elucidated. Application of guanosine 5'-[gamma-thio]triphosphate tetralithium salt (GTPgammaS), guanosine 5'-[beta-thio]diphosphate trilithium salt (GDPbetaS), the G-protein inhibitor suramin and pertussis toxin (PTX) demonstrated the involvement of the PTX-insensitive G-protein in the signal transduction pathway mediating MIP effects. Both G-protein alpha(i) and betagamma subunits were identified in D-neurons of Helix pomatia by immunoblotting. Their role in signal transduction was shown in electrophysiological experiments, which supported the notion that, in addition to the Galpha subunit, the betagamma dimer also participates in the neuropeptide-induced activation of K-channels in snail neurons. Finally, neuropeptide-activated responses were inhibited by the activation of adenylyl cyclase and by blockers of the phospholipase pathway. We suggest that bifurcation of the signal transduction takes place at the level of G-protein subunits. The alpha subunit may have a direct effect on adenylyl cyclase, while the betagamma subunit may have a direct effect on phospholipase enzymes.

Cannabinoid receptor agonists potentiate action potential‐independent release of GABA in the dentate gyrus through a CB1 receptor‐independent mechanism

“…1996; Freissmuth et al . 1996; Chung & Kermode, 2005; Kiss, 2005; Wang & Hatton, 2007). Our results indicated that the percentage of runs in which WIN55,212‐2 increased mIPSC frequency by ≥1Hz dropped from 41% (7 of 17) in control conditions to 0% (0 of 10) in slices treated with suramin.…”

“…If the novel effect of cannabinoid agonists described here is not mediated by CB1 receptors, CB2 receptors, or TRPV1 receptors, does not require non-specific effects on cell membranes, and is not likely to be produced by a specific interaction with a non-GPCR target, then we must consider the possibility that it could require specific activation of an as yet unidentified GPCR. As a first step towards evaluating that hypothesis, we examined the effect of bath applied WIN55,212-2 (5 μM) on mIPSCs (ruthenium red absent) in slices that had been preincubated for 20 min in 20 μM suramin, a compound that has previously been shown to effectively uncouple G-proteins from their effectors Freissmuth et al 1996;Chung & Kermode, 2005;Kiss, 2005;Wang & Hatton, 2007). Our results indicated that the percentage of runs in which WIN55,212-2 increased mIPSC frequency by ≥1Hz dropped from 41% (7 of 17) in control conditions to 0% (0 of 10) in slices treated with suramin.…”

FMRFamide regulates oscillatory activity of the olfactory center in the slug

“…1B). Previously, the 100 μ m concentration of mBPB was reported to be suitable in studies of the CNS of two other molluscs, Aplysia and Helix (Volterra & Siegelbaum, 1988; Kiss, 2005). It should be noted that, if a high concentration (e.g.…”