Some effects of lead at mammalian neuromuscular junction

Abstract

The effect of lead on transmitter release was investigated in a rat phrenic nerve-hemidiaphragm preparation using conventional microelectrode techniques. Lead reduced the number of quanta released by a nerve stimulus (m) in a dose-dependent fashion. As extracellular Ca2+ concentration ([Ca2+](o)) was varied in the absence of lead, a linear relationship between ln(m) and ln([Ca2+](o)) was obtained. Lead shifted the relationship between ln(m) and ln([Ca2+](o)) to the right without altering the slope. This suggested lead competed with Ca2+, which was confirmed by using a modified Lineweaver-Burk plot. Lead inhibits Ca2+ entry into frog sympathetic preganglionic nerve terminals, and a similar me..