Ionizing radiation induces migration of glioblastoma cells by activating BK K(+) channels.

BACKGROUND AND PURPOSE: Glioblastoma cells express high levels of Ca(2+)-activated BK K(+) channels which have been proposed to be indispensable for glioblastoma proliferation and migration. Since migration of glioblastoma cells is reportedly stimulated by ionizing radiation (IR), we tested for an IR-induced increase in BK channel activity and its effect on cell migration. MATERIALS AND METHODS: T98G and U87MG cells were X-ray-irradiated with 0-2 Gy, BK channel activity was assessed by patch-clamp recording, migration by trans-well migration assay, and activation of the Ca(2+)/calmodulin-dependent kinase II (CaMKII) by immunoblotting. RESULTS: IR dose-dependently stimulated migration of glioblastoma cells which was sensitive to the BK channel inhibitor paxilline. Ca(2+)-permeabilization of T98G cells activated up to 350 BK channels per cells. Importantly, IR stimulated an increase in BK channel open probability but did not modify the total number of channels. Moreover, IR activated CaMKII in a paxilline-sensitive manner. Finally, inhibition of CaMKII by KN-93 abolished the IR-stimulated migration. CONCLUSIONS: We conclude that IR stimulates BK channel activity which results in activation of CaMKII leading to enhanced glioblastoma cell migration.

Photogeneration of membrane potential hyperpolarization and depolarization in non-excitable cells.

We monitored femtosecond laser induced membrane potential changes in non-excitable cells using patchclamp analysis. Membrane potential hyperpolarization of HeLa cells was evoked by 780 nm, 80 fs laser pulses focused in the cellular cytoplasm at average powers of 30-60 mW. Simultaneous detection of intracellular Ca2+ concentration and membrane potential revealed coincident photogeneration of Ca2+ waves and membrane potential hyperpolarization. By using non-excitable cells, the cell dynamics are slow enough that we can calculate the membrane potential using the steady-state approximation for ion gradients and permeabilities, as formulated in the GHK equations. The calculations predict hyperpolarization that matches the experimental measurements and indicates that the cellular response to laser irradiation is biological, and occurs via laser triggered Ca2+ which acts on Ca2+ activated K+ channels, causing hyperpolarization. Furthermore, by irradiating the cellular plasma membrane, we observed membrane potential depolarization in combination with a drop in membrane resistance that was consistent with a transient laser-induced membrane perforation. These results entail the first quantitative analysis of location-dependent laser-induced membrane potential modification and will help to clarify cellular biological responses under exposure to high intensity ultrashort laser pulses.