Luzindole, a melatonin receptor antagonist, inhibits the transient outward K+ current in rat cerebellar granule cells.

The inhibitory effect of the melatonin receptor antagonist luzindole on voltage-activated transient outward K(+) current (I(K(A))) was investigated in cultured rat cerebellar granule cells using the whole cell voltage-clamp technique. At the concentration of 1 microM to 1 mM, luzindole reversibly inhibited I(K(A)) in a concentration-dependent manner. In addition to reducing the current amplitude of I(K(A)),luzindole accelerated the fast inactivation of I(K(A)) channels and shifted the curves of voltage-dependent steady-state activation and inactivation of I(K(A)) by +6.6 mV and -7.0 mV, respectively. The inhibitory effect of luzindole was neither use-dependent nor voltage-dependent, suggesting that the binding affinity of luzindole to I(K(A)) channels is state-dependent. Including luzindole in the pipette solution, or extracellular application of 4 P-PDOT, an antagonist of melatonin receptors, did not change the luzindole-induced inhibitory effect on the I(K(A)) current, indicating that luzindole exerts its channel blocking inhibitory action at the extracellular mouth of the channel, and that the effect is not due to action of the melatonin receptors. Our data are the first demonstration that luzindole is able to block transient outward K(+) channels in rat cerebellar granule cells in a state-dependent manner, likely associated with extracellular interaction of the drug with the I(K(A)) inactivation gate.

Photodynamic effects of 5-aminolevulinic acid and its hexylester on several cell lines.

5-aminolevulinic acid (ALA) and its hexyl-ester (He-ALA) has shown promising results in photodynamic detection and therapy of tumors. In this work, the photodynamic effects of ALA and He-ALA on neuroblastoma cells, hepatoma cells and fibroblast cells were comparatively studied. With the detection of fluorescence emission spectra, protoporphyrin IX (PpIX) induced by ALA or He-ALA was observed in these three cell lines. Confocal laser scanning microscope showed the diffuse PpIX fluorescence in cytoplasm of neuroblastoma cells. The kinetics of PpIX accumulation were different in these three kinds of cells. The PpIX content in hepatoma cells and fibroblast cells continuously increased with the incubation time of drugs until 12 h, while in neuroblastoma cells the PpIX content saturated around 8 h after incubation with ALA or He-ALA. In addition, the PpIX concentration in neuroblastoma cells was obviously higher than that in hepatoma cells and fibroblast cells, indicating that the PpIX production is cell line dependent. When incubated with ALA and irradiated with light, near 90% neuroblastoma cells were destroyed, while for hepatoma cells and fibroblast cells the death rate was around 50%. The results demonstrate that neuroblastoma cells are more sensitive to ALA-PDT and the neuro-tumor cells may be well suited for the treatment of ALA mediated photosensitization. Comparing to ALA, He-ALA can reach the similar results concerned PpIX production and PDT damaging in all three kinds of cells but with 10 times lower incubation concentration, demonstrating that He-ALA has higher efficiency than ALA on inactivation of cancer cells in vitro.