Soluble or bound laminin elicit in human neuroblastoma cells short- or long-term potentiation of a K+ inwardly rectifying current: Relevance to neuritogenesis

Changes in the resting potential (V-REST) 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. I-IR 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 (G(L)). Successively, the persistence of a high I-IR conductance and the decrease of G(L) progressively bring V-REST from -12 to similar 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 I-IR, without any increase in G(L): this caused a rapid, transient hyperpolarisation of V-REST. The effects of bLN and sLN were mimicked by antibodies raised against the integrin beta(1) subunit, suggesting a specific integrin-mediated mechanism. In fact, when bound to the culture dishes, these antibodies simultaneously activated the I-IR and G(L), whereas in soluble form they only activated I-IR. Cells adherent to bLN emitted neurites, a process impaired by the block of I-IR by E-4031 and Cs+. On the whole data suggest that the integrin-mediated activation of I-IR plays a crucial role in the commitment to neuritogenesis of neuroblastoma cells, independently on the effects of this activation On V-REST.