Elevation in presynaptic Ca2+ level accompanying initial nerve-muscle contact in tissue culture.
Nerve-muscle cocultures were used to study the relationship between neuronal Ca2+ level and the earliest nerve-muscle interaction. Xenopus spinal cord neurons were loaded with Ca2+ indicators and monitored by digital video microscopy as a myoball was manipulated into contact with it. Transmitter release was measured from the myoball by whole-cell recording. We observed a 1.5- to 6-fold increase in Ca2+ level in the neurite upon contact with a myoball. Fifty percent of the pairs showing Ca2+ elevation were also positive for neurotransmission. This Ca2+ rise was suppressed by lifting away the myoball, by Ca(2+)-free solution, or by suramin, a polyanionic compound that interferes with cell surface receptors. This suppression was accompanied by a reduction in transmitter release. The specificity of the nerve-muscle contact-induced Ca2+ rise was shown by its absence upon neuron-neuron contact. Naturally formed nerve-muscle contacts also showed an elevation in presynaptic Ca2+ level. Thus, this elevation appears to be a physiological step in the early stage of synaptogenesis and is likely mediated by muscle-derived molecules.
Dai
Z
Z
Department of Cell Biology and Anatomy and Curriculum in Neurobiology, University of North Carolina, Chapel Hill 27599.
Peng
H B
HB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D005456:Fluorescent Dyes; D016257:Fura-2; D008856:Microscopy, Fluorescence; D009132:Muscles / Q000196:embryology / Q000502:physiology; D016501:Neurites / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology; D013569:Synapses / Q000502:physiology*; D014981:Xenopus / Q000196:embryology
D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents; D013498:Suramin; D002118:Calcium; D016257:Fura-2