Bradykinin-evoked non-specific cationic current in neuroblastoma-glioma hybrid (NG108-15) cells and its down-regulation through differentiation

Effects of bradykinin (BK) on the membrane conductance and level of cytoplasmic free Ca²⁺ in undifferentiated and differentiated neuroblastoma-glioma hybrid (NG108-15) cells were studied using the nystatin-perforated patch-clamp technique and fura-2 fluorometry. Under voltage clamp at -20 mV, undifferentiated cells responded to BK at > 10^-9 M, producing a biphasic current composed of an apamin-sensitive Ca²⁺ -activated K⁺ outward current and non-specific cationic inward current. Both current components corresponding to a biphasic elevation of [Ca²⁺]_i were completely prevented by an intracellular perfusion with EGTA (1 mM) under conventional whole cell recording condition. Undifferentiated cells revealed almost no voltage sensitive Ca²⁺ current. In NG108-15 cells differentiated with 8-Br-cyclic AMP (1 mM) or rolipram (1 mM), an inhibitor of type IV phosphodiesterase, BK concentration required for the non-specific cationic current with amplitude of > 100 pA was much greater than that of undifferentiated cells. This suggests that the differentiated cells decreased BK-sensitivity in induction of the non-specific cationic current. The non-specific cationic channel is suggested to play roles as a source of Ca²⁺ entry in undifferentiated NG108-15 cells.