Intrathecal anaesthesia alters intracellular Ca2+/Mg2+ homeostasis in the spinal cord neurones of experimental rats.

Background and Objective: The effect of anaesthesia induced by intrathecal injection of 6.3% MgSO4 or 4% lidocaine on intracellular electrolyte homeostasis in spinal cord neurones of a rat model was investigated.
Methods: Intracellular Ca2+, Mg2+, Na+ and K+ concentrations were determined at different times after intrathecal administration of NaCl (saline, a control group), MgSO4 or lidocaine.
Results: In both thoracic and lumbar spinal cord segments, Ca2+ concentrations rose significantly 30 min and 2 h after 6.3% MgSO4 injection, and after 24 h were still significantly increased compared with the values obtained from the control group which were subjected to sham 'anaesthesia' by saline injection (172, 121 and 108 ng mg-1 protein vs. control 23 ng mg-1 protein, respectively, in the thoracic segment and 222, 229 and 176 ng mg-1 protein vs. control 43 ng mg-1 protein, respectively, in the lumbar segment). Lidocaine injection also produced a significant increase in intracellular Ca2+ in the thoracic and lumbar spinal cord segments (69, 64 and 53 ng mg-1 protein vs. control 33.4 ng mg-1 protein and 26, 94 and 46 ng mg-1 protein vs. 23 ng mg-1 protein respectively). Only a modest rise in intracellular Mg2+ was observed after intrathecal MgSO4 or lidocaine injection (27 ng mg-1 protein vs. 23 ng mg-1 protein). Na+ and K+ concentrations decreased 24 h after MgSO4 and 1 h after lidocaine injection.
Conclusion: Intrathecal anaesthesia by MgSO4 or lidocaine alters intracellular electrolyte homeostasis in spinal cord neurones of experimental rats. A possible common mechanism of action via Ca2+ ion channels is discussed.