Pharmacologic inhibition of twin-pulse facilitation of release of transmitter quanta at the mouse neuromuscular junction.
1. The frequency (F,s-1) of miniature endplate potentials and the quantal content (m) of endplate potentials were simultaneously measured intracellularly at mouse diaphragm endplates in a bath solution that contained 0.6 mM Ca2+ ions and 5 mM Mg2+ ions. 2. Twin pulses at 4-ms intervals gave the quantal contents of the first (m1) and second (m2) responses. The ratio of m2/m1 was taken as an indicator of the temporal facilitation of the release of transmitter. 3. Lead ions (Pb2+; 10 microM), bis (o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; loaded for 60 min at 200 microM), and chlortetracycline (CTC; loaded for 30 min at 80 microM) reduced the values of F and m2/m1. Pb2+ ions and CTC reduced the value of m, whereas BAPTA did not.omega-Agatoxin (omega AGT; 10 ng/ml) reduced the value of m without affecting F or m2/m1. 4. These results suggest that synaptic facilitation is modifiable by agents that can affect systems which buffer intracellular levels of Ca2+ ions.
Nishimura
M
M
Department of Pharmacology, University of Obihiro School of Veterinary Medicine, Japan.
Taquahashi
Y
Y
Ishii
K
K
Satoh
E
E
Shimizu
Y
Y
Saitoh
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002751:Chlortetracycline / Q000494:pharmacology; D003864:Depression, Chemical; D003964:Diaphragm / Q000294:innervation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D007854:Lead / Q000494:pharmacology; D008297:Male; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects* / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010791:Phrenic Nerve / Q000502:physiology
D018377:Neurotransmitter Agents; D007854:Lead; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D002751:Chlortetracycline