Dibenzo[1,2,5]thiadiazepines are non-competitive GABAA receptor antagonists.

A new process for obtaining dibenzo[c,f][1,2,5]thiadiazepines (DBTDs) and their effects on GABA(A) receptors of guinea pig myenteric neurons are described. Synthesis of DBTD derivatives began with two commercial aromatic compounds. An azide group was obtained after two sequential reactions, and the central ring was closed via a nitrene to obtain the tricyclic sulfonamides (DBTDs). Whole-cell recordings showed that DBTDs application did not affect the holding current but inhibited the currents induced by GABA (I(GABA)), which are mediated by GABA(A) receptors. These DBTDs effects reached their maximum 3 min after application and were: (i) reversible, (ii) concentration-dependent (with a rank order of potency of 2c = 2d > 2b), (iii) mediated by a non-competitive antagonism, and (iv) only observed when applied extracellularly. Picrotoxin (which binds in the channel mouth) and DBTDs effects were not modified when both substances were simultaneous applied. Our results indicate that DBTD acted on the extracellular domain of GABA(A) channels but independent of the picrotoxin, benzodiazepine, and GABA binding sites. DBTDs used here could be the initial model for synthesizing new GABA(A) receptor inhibitors with a potential to be used as antidotes for positive modulators of these receptors or to induce experimental epilepsy.

Modulation of the voltage-gated potassium channel Kv2.1 by the anti-tumor alkylphospholipid perifosine.

BACKGROUND: The aim of the present study was to assess the effects of perifosine-a third generation alkylphospholipid analog with anti-tumor properties-on the activity of Kv2.1 channels. METHODS: The whole-cell patch clamp technique was applied to follow the modulatory effect of perifosine on Kv2.1 channels expressed in HEK293 cells. RESULTS: Obtained data provide evidence that perifosine application decreases the whole cell Kv2.1 currents in a concentration-independent manner. Perifosine induces a hyperpolarizing shift in the voltage dependence of Kv2.1 channels inactivation without altering the voltage dependence of channels activation. The kinetics of Kv2.1 closed-state inactivation was accelerated by perifosine, with no significant effects on the recovery rate from inactivation. CONCLUSIONS: Taken together, these results show that perifosine modified the Kv2.1 inactivation gating resulting in a decrease of the current amplitude. These data will help to elucidate the mechanism of action of this promising anti-cancer drug on ion channels and their possible implications.

Two suramin binding sites are present in guinea pig but only one in murine native P2X myenteric receptors.

Whole-cell patch clamp recordings were used to characterise the physiological and pharmacological properties of P2X receptors of mouse and guinea pig myenteric neurons from the small intestine. ATP application induced a rapid inward current in 95% of recorded neurons of both species when were voltage clamped at -60 mV. Concentration-response curves for ATP (1-3000 microM) yielded EC(50) values of 114 and 115 microM for mouse and guinea pig myenteric neurons, respectively, with a Hill coefficient value of 1.02 and 0.79, respectively, which were not significantly different of unity. alpha,beta-methylene ATP (100 microM) was virtually inactive in both species. Pyridoxalphophate-6-azophenyl-2',4'-disulphonic acid (0.01-30 microM) inhibited the ATP-induced currents (I(ATP)) with a different potency; being the IC(50) 0.6 and 1.8 microM in mouse and guinea pig, respectively. In mouse myenteric neurons, I(ATP) were inhibited by suramin whereas in guinea pig neurons we observed two effects, potentiation and inhibition of these currents. On guinea pig, both effects of suramin had different recovering kinetics and concentration dependency, indicating that they are mediated by at least two different binding sites. Our observations indicate that myenteric P2X receptors in these two species have different pharmacological properties.