Gamma-dendrotoxin blocks large conductance Ca2+-activated K+ channels in neuroblastoma cells.
In N1E 115 neuroblastoma cells, gamma-dendrotoxin (DTX, 200 nM) blocked the outward K(+) current by 31.1 +/- 3.5% (n = 4) with approximately 500 nM Ca(2+) in the pipet solution, but had no effect on the outward K(+) current when internal Ca(2+) was reduced. Using a ramp protocol, iberiotoxin (IbTX, 100 nM) inhibited a component of the whole cell current, but in the presence of 200 nM gamma-DTX, no further inhibition by IbTX was observed. Two types of single channels were seen using outside-out patches when the pipette free Ca(2+) concentration was approximately 500 nM; a 63 pS and a 187 pS channel. The 63 pS channel was TEA-, IbTX- and gamma-DTX-insensitive, while the 187 pS channel was blocked by 1 mM TEA, 100 nM IbTX or 200 nM gamma-DTX. Both channels were activated by external application of ionomycin, when the pipet calcium concentration was reduced. gamma-DTX (200 nM) reduced the probability of openings of the 187 pS channel, with an IC(50) of 8.5 nM. In GH(3) cells gamma-DTX (200 nM) also blocked an IbTX-sensitive component of whole-cell K(+) currents. These results suggest that gamma-DTX blocks a large conductance Ca(2+) activated K(+) current in N1E 115 cells. This is the first indication that any of the dendrotoxins, which have classically been known to block voltage-gated (Kv) channels, can also block Ca(2+) activated K(+) channels.
Inglis
V
V
Department of Physiology, University of Alberta, Faculty of Medicine, Edmonton, Alberta, Canada T6G 2H7.
Karpinski
E
E
Benishin
C
C
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D014407:Tumor Cells, Cultured
D004338:Drug Combinations; D009498:Neurotoxins; D010455:Peptides; D024681:Potassium Channels, Calcium-Activated; C081639:dendrotoxin, gamma; C064719:iberiotoxin