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Abstract
Changes in the resting potential (Vrest) and in the underlying ionic conductances were measured by the patch-clamp technique in SH-SY5Y human neuroblastoma cells exposed to substrate-bound or soluble Laminin (bLN: sLN), as compared to integrin-independent substrates (polylysine (PL); bovine serum albumin (BSA)). While PL and BSA were ineffective, both forms of LN caused an early (5-15 min) activation of a peculiar type of Inwardly Rectifying K− current (I,ir) characterised by a voltage-dependent inactivation in the range of membrane potentials around —50/0 mV. Iir was blocked by Cs+ ions and by the antiarrhythmic drug E-4031, a specific inhibitor of the HERG-codified channels. In cells adherent to bLN, I,ir potentiation (85%) persisted for 90-120 min and was accompanied by a similar, but transient, increase in the leakage conductance (Gl). Successively, the persistence of a high Iir conductance and the decrease of Gl progressively bring Vrest from –12 to -30 mV in about 120 min. On the other hand, in cells adherent to PL, exposure to sLN produced a similar but not persistent activation of Iir, without any increase in Gl: this caused a rapid, transient hyperpolarisation of Vrest The effects of bLN and sLN were mimicked by antibodies raised against the integrin β1 subunit, suggesting a specific integrin-mediated mechanism. In fact, when bound to the culture dishes, these antibodies simultaneously activated the Iir and Gl, whereas in soluble form they only activated Iir. Cells adherent to bLN emitted neurites, a process impaired by the block of Iir by E-4031 and Cs+. On the whole data suggest that the integrin-mediated activation of Iir plays a crucial role in the commitment to neuritogenesis of neuroblastoma cells, independently on the effects of this activation on Vrest.