Selective inhibition of the slow K+ current at motor nerve ending by plasma from a myasthenia gravis patient.
The effect of plasma from a myasthenia gravis (MG) patient, containing anti-presynaptic membrane receptor (PsmR) antibody on the membrane currents of motor nerve ending was investigated in mouse intercostal nerve triangularis sterni preparations by perineurial recording. After inhibition of both the fast K+ current and Ca(2+)-dependent K+ current by 30 mM Tetraethyl-ammonium (TEA) unmasked the voltage dependent fast Ca2+ current and the "Ca plateau", which was contributed by the voltage-dependent slow Ca2+ current and slow K+ current. Application of the MG plasma caused further prolongation and increase of the Ca plateau, due to blockage of the slow K+ current. This effect was observed immediately after the application and could be partially reversed by washing, whereas no change was found by addition of the plasma from healthy persons. When K+ current was completely blocked by 30 mM TEA and 300 microM 3,4-diaminopyridine (3,4-DAP), the fast Ca2+ current and the slow Ca2+ current were revealed. Neither the fast nor the slow Ca2+ current could be affected by the MG plasma; It was also shown that the MG plasma was devoid of noticeable effect on the voltage dependent Na+ current, fast K+ current as well as the Ca(2+)-dependent K+ current. So the effect of the MG plasma with antibody to PsmR was concluded to inhibit the slow K+ current selectively. As we knew, the beta-bungarotoxin binding protein was a kind of K+ channel, these results further confirmed that the beta-bungarotoxin binding protein should be the target of the antibody to PsmR found in the plasma of some patients suffering from MG.
Shi
Y
Y
Shanghai Institute of Physiology, Chinese Academy of Sciences.
Xu
Y
Y
Xu
K
K
D000328:Adult; D000818:Animals; D004594:Electrophysiology; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism*; D009157:Myasthenia Gravis / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
D015221:Potassium Channels; D017661:Receptors, Presynaptic; D015222:Sodium Channels