Non-competitive antagonism of calcium by magnesium ions at the K(+)-depolarised mouse neuromuscular junction.
The effect of raising the external Ca2+ concentration on miniature end-plate potential (m.e.p.p.) frequency was measured in the K(+)-depolarised mouse phrenic nerve/hemidiaphragm preparation in the presence of a range of Mg2+ concentrations. With increasing external Mg2+, a plot of external Ca2+ concentration vs. m.e.p.p. frequency was shifted to the right and the maximum frequency attained was reduced. A Schild plot of the data gave a slope factor close to two. These data suggest a non-competitive antagonism of Ca2+ by Mg2+ under these conditions.
Pearson
H A
HA
Department of Pharmacology, Royal Free Hospital School of Medicine, London, UK.
Wray
D
D
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D008274:Magnesium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*
D008274:Magnesium; D011188:Potassium; D002118:Calcium