Quantal stores of excitatory transmitter in nerve-muscle synapses of crayfish evaluated from high-frequency asynchronous quantal release induced by veratridine or high concentrations of potassium.
At single voltage-clamped opener muscle fibres of crayfish claw, 10-100 mumol/l veratridine increased within a few seconds the rate of asynchronous quantal release, ñ, of excitatory transmitter from ñ less than 1 quantum/s to ñ congruent to 10,000 quanta/s. Thereafter ñ declined exponentially either with a single, tau(2) congruent to 50 s, or with two time constants tau(1) congruent to 19 s, tau(2) congruent to 50 s. In total (t----infinity), about 0.3 million quanta were released by veratridine in a single short fibre of about 1 mm length. These values were estimated by means of the noise analysis technique and they agreed with equivalent parameters of release when 100 mmol/l K+ were used as release stimulus. Strong quantal release could be elicited only once in a single muscle by veratridine. Furthermore, the effect of veratridine on quantal release could be completely prevented by pretreatment with tetrodotoxin. In another nerve-muscle preparation of crayfish, the abdominal superficial extensor muscle, up to 3 million excitatory quanta could be released by veratridine in a single fibre. In the latter muscle veratridine-induced asynchronous quantal release was strongly dependent on the extracellular concentration of Ca2+ whereas in the claw opener dependence of quantal release on extracellular Ca2+ was negligible.
Finger
W
W
Physiologisches Institut, Technischen Universität München, Federal Republic of Germany.
Martin
C
C
D000818:Animals; D003400:Astacoidea / Q000502:physiology*; D004553:Electric Conductivity; D004558:Electric Stimulation; D009119:Muscle Contraction; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology*; D014702:Veratrine / Q000031:analogs & derivatives*
D015222:Sodium Channels; D013779:Tetrodotoxin; D014701:Veratridine; D014702:Veratrine; D011188:Potassium