Involvement of calcium in rhythmic activity induced by disinhibition in cultured spinal cord networks.
Disinhibition of rat spinal networks induces a spontaneous rhythmic bursting activity. The major mechanisms involved in the generation of such a bursting are intrinsic neuronal firing of a subpopulation of interneurons, recruitment of the network by recurrent excitation, and autoregulation of neuronal excitability. We have combined whole cell recording with calcium imaging and flash photolysis of caged-calcium to investigate the contribution of [Ca(2+)](i) to rhythmogenesis. We found that calcium mainly enters the neurons through voltage-activated calcium channels and N-methyl-D-aspartate (NMDA) channels as a consequence of the depolarization during the bursts. However, [Ca(2+)](i) could neither predict the start nor the termination of bursts and is therefore not critically involved in rhythmogenesis. Also calcium-induced calcium release is not involved as a primary mechanism in bursting activity. From these findings, we conclude that in the rhythmic activity induced by disinhibition of spinal cord networks, the loading of the cells with calcium is a consequence of bursting and does not functionally contribute to rhythm generation.
Darbon
Pascal
P
Departement of Physiology, University of Bern, CH-3012 Bern, Switzerland.
Pignier
Christophe
C
Niggli
Ernst
E
Streit
Jürg
J
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D007425:Intracellular Membranes / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D016202:N-Methylaspartate / Q000378:metabolism; D009415:Nerve Net / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010507:Periodicity; D051381:Rats; D013116:Spinal Cord / Q000502:physiology*
D015220:Calcium Channels; D007473:Ion Channels; D016202:N-Methylaspartate; D002118:Calcium