A study of properties of batrachotoxin modified sodium channels.
A further analysis of the effects of the steroidal alkaloid batrachotoxin (BTX) on sodium channels in frog node of Ranvier has been carried out under voltage-clamp conditions. The main properties of modified channels as compared with those of normal ones are as follows: The rate of channel closing is drastically decreased, whereas that of opening is changed slightly if at all; The steady-state voltage dependence of channel activation is shifted towards more negative potentials by 60-70 mV; Currents through modified channels do not show a decay during maintained depolarization as it is typical for normal channels. However modified channels retain the ability to partial inactivation as shown by experiments with depolarizing prepulses; Sodium against potassium selectivity beyond--20 mV suggesting either nonhomogeneity of the modified channels as for their kinetic and selectivity properties or potential-dependence of ionic selectivity for each channel; The selectivity sequence determined from peak current reversal potential measurements is as follows: H: Na :NH4:K = 528:1:0.47: :0.19; The effective pK value of proton block is decreased by about 0.4; 7) The sensitivity of the channels to tetrodotoxin (TTX) block is practically unchanged.
D000818:Animals; D001496:Batrachotoxins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004558:Electric Stimulation; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D009413:Nerve Fibers, Myelinated / Q000378:metabolism / Q000502:physiology; D009498:Neurotoxins / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D011898:Ranidae; D011901:Ranvier's Nodes / Q000187:drug effects
D001496:Batrachotoxins; D007473:Ion Channels; D009498:Neurotoxins; D011343:Procaine; D011188:Potassium; D002118:Calcium