Background and objective The effect of anaesthesia induced by intrathecal injection of 6.3% MgS04 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 NaCI (saline, a control group), MgS04 or lidocaine.

Results In both thoracic and lumbar spinal cord segments, Ca2+ concentrations rose significantly 30min 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 108ngmg−1 protein vs. control 23ngmg−1 protein, respectively, in the thoracic segment and 222, 229 and 176ngmg−1 protein vs. control 43ngmg−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 53ngmg−1 protein vs. control 33.4 ngmg−1 protein and 26, 94 and 46ngmg−1 protein vs. 23ngmg−1 protein respectively). Only a modest rise in intracellular Mg2+ was observed after intrathecal MgS04 or lidocaine injection (27ngmg−1 protein vs. 23ngmg−1 protein). Na+ and K+ concentrations decreased 24 h after MgS04and 1h after lidocaine injection.

Conclusion Intrathecal anaesthesia by MgS04 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.