Calcium channel currents in undifferentiated human neuroblastoma (SH-SY5Y) cells: actions and possible interactions of dihydropyridines and omega-conotoxin.
Ca2+ channel currents were recorded in undifferentiated human neuroblastoma (SH-SY5Y) cells with the whole-cell patch-clamp technique, using 10 mM Ba2+ as charge carrier. Currents were only evoked by depolarizations to -30 mV or more positive (holding potential -80 mV), inactivated partially during 200 ms depolarizing steps, and were abolished by 150 microM Cd2+. Currents could be enhanced by Bay K-8644 and partially inhibited by nifedipine, suggesting that they arose in part due to activation of L-type Ca2+ channels. Currents were also inhibited by the marine snail peptide omega-conotoxin GVIA (omega-CgTx). At a concentration of 10 nM inhibition by omega-CgTx was reversible, but at higher concentrations blockade was always irreversible. Although current inhibition by nifedipine was maximal at 1 microM, supramaximal concentrations reduced the inhibitory actions of omega-CgTx in a concentration-dependent manner. Ca2+ channel currents evoked from a holding potential of -50 mV showed no inactivation during 200 ms depolarizations but declined in amplitude with successive depolarizing steps (0.2 Hz). Current amplitudes could be restored by returning the holding potential to -80 mV. Currents evoked from -50 mV were inhibited by nifedipine and omega-CgTx to a similar degree as those evoked from -80 mV. Our results indicate that undifferentiated SH-SY5Y cells possess L- and N-type Ca2+ channels which can be distinguished pharmacologically but cannot be separated by using depolarized holding potentials. Furthermore, these data suggest that nifedipine has a novel action to inhibit blockade of N-type channels by omega-CgTx.
Department of Pharmacology, Leeds University, UK.
H L
HL
Reeve
P F
PF
Vaughan
C
C
Peers
D001932:Brain Neoplasms / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D002454:Cell Differentiation; D004095:Dihydropyridines / Q000494:pharmacology*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009447:Neuroblastoma / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D010455:Peptides; D020866:omega-Conotoxin GVIA