Graham Henry Timms

Actions of arginine polyamine on voltage and ligand-activated whole cell currents recorded from cultured neurones.

1 Toxins from invertebrates have proved useful tools for investigation of the properties of ion channels. In this study we describe the actions of arginine polyamine which is believed to be a close analogue of FTX, a polyamine isolated from the American funnel web spider, Agelenopsis aperta. 2 Voltage‐activated Ca2+ currents and Ca2+‐dependent Cl− currents recorded from rat cultured dorsal root ganglion neurones were reversibly inhibited by arginine polyamine (AP; 0.001 to 100 μm). Low voltage‐activated T‐type Ca2+ currents were significantly more sensitive to AP than high voltage‐activated Ca2+ currents. The IC50 values for the actions of AP on low and high voltage‐activated Ca2+ currents were 10 nm and 3 μm respectively. AP was equally effective in inhibiting high voltage‐activated currents carried by Ba2+, Sr2+ or Ca2+. However, AP‐induced inhibition of Ca2+ currents was attenuated by increasing the extracellular Ca2+ concentration from 2 mm to 10 mm. 3 The actions of AP on a Ca2+‐independent K+ current were more complex, 1 μm AP enhanced this current but 10 μm AP had a dual action, initially enhancing but then inhibiting the K+ current. 4 γ‐Aminobutyric acid‐activated Cl− currents were also reversibly inhibited by 1 to 10 μm AP. In contrast N‐methyl‐d‐aspartate currents recorded from rat cultured cerebellar neurones were greatly enhanced by 10 μm AP. 5 We conclude that at a concentration of 10 nm, AP is a selective inhibitor of low threshold T‐type voltage‐activated Ca2+ currents. However, at higher concentrations 1–10 μm AP interacts with ion channels or other membrane constituents to produce a variety of actions on both voltage and ligand gated ion channels.

New multi-bridged cryptands: Polyazamacrocyclic schiff bases formed in a tetrapode capping reaction

Abstract Multi-bridged cryptands were formed in one step by condensation of two moles of a tetraaldehyde with four moles of a triamine. This is the first example of a tetrapode capping reaction.

Stereoselectivity in the Catalytic Hydrogenation of an Enamine. Selective Formation of Either CIS- or trans- Tertiary Amines

Abstract Conditions have been found where catalytic hydrogenation of the enamine (II) may produce either the trans-2- (3,4-dichlorophenyl) -3 -NN-dimethylaminomethylbicyclo[2,2,2]octane exclusively, or the cis-isomer with high stereoselectivity.

INHIBITORY ACTIONS OF SYNTHESISED POLYAMINE SPIDER TOXINS AND THEIR ANALOGUES ON NEURONAL VOLTAGE-ACTIVATED CALCIUM CURRENTS

Abstract The whole cell variant of the patch-clamp technique was used to investigate the actions of polyamine spider toxins and their analogues on high voltage-activated Ca 2+ currents. The actions of synthesised FTX (putative natural toxin from the American funnel web spider), sFTX-3.3, Orn-FTX-3.3 and Lys-FTX-3.3 (synthetic analogues of FTX) were studied using cultured dorsal root ganglion neurones from neonatal rats, C2D7 cells (HEK293 cells stably coexpressing recombinant human N-type voltage-activated Ca 2+ channel, α 1B-1 - α 2b δβ 1b subunits) and freshly isolated cerebellar Purkinje neurones. In dorsal root ganglion neurones, sFTX-3.3 (10 μ M) inhibited high voltage-activated Ca 2+ currents evoked by depolarisations to 0 mV from a holding potential of −90 mV. Partial overlap in Ca 2+ current sensitivity to the polyamine sFTX-3.3 and the peptide spider toxin ω -Aga IVA was observed. However, evidence also suggests sFTX-3.3 and ω -Aga IVA do not show complete pharmacological overlap and that distinct parts of the Ca 2+ current are sensitive to one of two inhibitors. The arginine group on sFTX-3.3 appears to be important for its inhibitory action on Ca 2+ currents, because analogues where this amino acid was replaced with either ornithine (Orn-FTX-3.3) or lysine (Lys-FTX-3.3) were relatively inactive at concentrations below 1 mM. Synthesised FTX (100 μ M) was inactive as an inhibitor of Ca 2+ currents recorded from dorsal root ganglion and only produced modest effects in Purkinje neurones and C2D7 cells. At a concentration of 1 mM, nonselective actions were observed that indicated that synthesised FTX and sFTX-3.3 could reversibly inhibit both N- and P-type Ca 2+ channels equally well. In conclusion, the potency of polyamines as nonselective inhibitors of Ca 2+ channels is in part determined by the presence of a terminal arginine, and this may involve an interaction between terminal guanidino groups with Ca 2+ binding sites.