Argiopine blocks glutamate-activated single-channel currents on crayfish muscle by two mechanisms.
1. The effect of the spider venom argiopine on L-glutamate-activated membrane channels of crayfish muscle was investigated using the patch-clamp technique. 2. When 10(-2) M-glutamate and 10(-9) M-argiopine were contained in the pipette solution of a cell-attached patch, bursts of openings of excitatory channels appeared after formation of the patch. These bursts ceased abruptly after variable periods of time in the range of 5 min. Higher concentrations of argiopine (up to 10(-6) M) blocked more rapidly, approximately in proportion to concentration. 3. The block of excitatory channels could be partially or completely reversed by hyperpolarizing the membrane by up to -190 mV from the resting potential. The time constant of the recovery of channel opening decreased with increasing hyperpolarization and was 2 ms with -160 mV hyperpolarization. Switching back from the hyperpolarized level to the resting potential, the time constant for the resulting block was about 3 s (10(-7) M-argiopine). Potential-dependent block by argiopine with similar characteristics was also observed in outside-out patches. 4. Up to argiopine concentrations of 10(-7) M the kinetics of channel openings and of bursts measured in pre-block periods or during reversal of the block by hyperpolarization were indistinguishable from controls. 5. When the potential-dependent block observed in the presence of 10(-6) M-argiopine and 10(-2) M-glutamate was reversed by hyperpolarization, additional short closings occurred during bursts. This 'flickering block' did not change burst length appreciably, but an additional open time component (tau = 0.1 ms) appeared and the average open time per burst was reduced. 6. At least two reaction steps seem necessary to model the behaviour of the potential-dependent block. The flickering block may be described as intermittent blocking of the channel which does not interfere with the reactions between glutamate and the channel.
Antonov
S M
SM
Physiologisches Institut der Technischen Universität München, FRG.
Dudel
J
J
Franke
C
C
Hatt
H
H
D000818:Animals; D001180:Arthropod Venoms / Q000494:pharmacology*; D003400:Astacoidea / Q000502:physiology*; D004594:Electrophysiology; D005971:Glutamates / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology*; D011073:Polyamines / Q000494:pharmacology*; D013111:Spider Venoms / Q000494:pharmacology*
D001180:Arthropod Venoms; D005971:Glutamates; D007473:Ion Channels; D009842:Oligopeptides; D011073:Polyamines; D013111:Spider Venoms; C050570:argiopine