Influence of muscle cells on the development of calcium currents in Xenopus spinal neurons.
The influence of muscle cells on the development of voltage-dependent Ca2+ currents was investigated in Xenopus spinal neurons grown in neuron muscle co-cultures or in muscle-free cultures. Whole-cell currents were separated into low- and high-voltage-activated currents. Developmental changes were assessed by comparing the results obtained at two different periods after plating: 5-10 h (young neurons) and 20-30 h (mature neurons). Our results show a drop in the incidence of low-voltage-activated Ca2+ current with time in both environments: the fraction of young versus mature neurons expressing this current was 67% and 36% in neuron-muscle co-cultures, and 69% and 23% in muscle-free cultures. In both neuron muscle and muscle-free cultures, the density of low-voltage-activated Ca2+ current (when expressed) did not change during the development. In contrast, the density of high-voltage-activated Ca2+ currents increased more than two-fold during the first 30 h in neuron muscle co-cultures, but remained unchanged in muscle-free cultures. This difference was not related to neuronal growth since the increase in neuronal membrane capacitance with time was similar in the two environments. In addition, direct cell-cell interaction through the establishment of functional neuron-muscle synaptic contacts did not further modify the overall expression of high-voltage-activated Ca2+ currents. In conclusion, these results suggest the presence of diffusible factors in neuron muscle co-cultures which up-regulate the expression of high-voltage-activated Ca2+ currents during neuronal development, but do not have any effect on low-voltage-activated Ca2+ currents.
Lhuillier
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Laboratoire de Physiologie Générale, Faculté des Sciences, Université Paris XII-Val de Marne, Créteil, France.
Tabti
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D000818:Animals; D015220:Calcium Channels / Q000096:biosynthesis* / Q000502:physiology; D002478:Cells, Cultured; D018920:Coculture Techniques; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D008564:Membrane Potentials; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology*; D014982:Xenopus laevis
D015220:Calcium Channels