title: Dendrotoxin: a selective blocker of a non-inactivating potassium current in guinea-pig dorsal root ganglion neurones.
abstract: The voltage clamp technique was used to study the effects of dendrotoxin (DTX) on outward potassium currents in internally perfused dorsal root ganglion neurones of guinea-pig. Sodium currents were eliminated by tetrodotoxin (TTX, 2 mumol/l), calcium currents and calcium-activated potassium conductances were abolished by intracellular perfusion of cells with KF. Depolarizing voltage shifts from a holding potential of -90 mV yielded a fast transient outward current (IfK) and a delayed non-inactivating outward current (IsK). These currents could be separated by shifting the membrane potential to -50 mV, where IfK was almost completely inactivated. DTX, at concentrations of 0.14-1.4 nmol/l selectively reduced a portion of the non-inactivating potassium current, leaving the transient outward current unaffected. Once manifested, the action of DTX could not be reversed by washing. The I-V characteristic of the current blocked by DTX is almost linear and quite different from the one of the 'DTX-resistant' portion of IsK, which shows a non-linear I-V curve. Tetraethylammonium (TEA, 30 mmol/l) strongly reduced IfK and IsK. However, subsequent application of DTX was still able to further reduce IsK. 3,4-diaminopyridine (3,4-DAP, 500 mumol/l) unselectively reduced IfK and a portion of IsK. The remainder of the latter could not further be reduced by DTX, suggesting a similar action of the two blockers on non-inactivating potassium currents. From the results presented, it is suggested that dendrotoxin selectively blocks a non-inactivating subtype of potassium channel.
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives*; D000077770:Amifampridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D004546:Elapid Venoms / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000187:drug effects*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D004546:Elapid Venoms; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D019789:Tetraethylammonium; C020273:dendrotoxin; D015761:4-Aminopyridine; D000077770:Amifampridine; D011188:Potassium