Two Types of High Voltage-activated Calcium Channels in SH-SY5Y Human Neuroblastoma Cells

Voltage-activated calcium channel currents were recorded from differentiated human neuroblastoma cells. SK-N-SH-SY5Y (SH-SY5Y) line, using patch-clamp techniques. Experimental solutions were designed to suppress sodium and potassium channel currents, and barium ions were used as the charge carrier. Two distinct types of calcium channel currents (N- and L-like) were identified based on their time-dependent inactivation, pharmacology and single-channel conductances. N- and L-like calcium channel currents were evoked by step depolarizing pulses to potentials more positive than -40 mV from a holding potential of -100 mV. The N-like component showed time-dependent inactivation during maintained depolarization with a time constant of tau f approximately 100 ms, whereas the L-like currents showed very slow inactivation with a time constant of tau s approximately 1,000 ms. Steady-state inactivation of currents evoked from a holding potential of -100 mV had two distinct components. One component involved the reduction of the transient current and had a half-maximal current at approximately -66 mV, whereas the other component involved the reduction of the steady-state current in the range of -35 to 0 mV with a half-maximal current at approximately -17 mV. Bay K 8644 (5 microM), had two distinct actions, one was the increase (50%) of the current associated with a depolarizing pulse to +10 mV. The second action was the increase in the peak amplitude of the tail current and the slowing of the deactivation kinetics. Omega-conotoxin at 1 microM irreversibly reduced the N-like current, sparing a component that was still sensitive to 5 microM Bay K 8644. The single-channel currents recorded with the cell-attached configuration of the patch clamp revealed two distinct conductances: a large approximately 28 pS and a small approximately 16 pS, corresponding to the L- and N-like channels, respectively. Bay K 8644 at 5 microM increased the mean open time of L-like single channel currents without changing single-channel conductance.