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 i njection of 6.3% MgSO4 or 4% lidocaine on intracellular electrolyte homeost asis 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 con trol group), MgSO4 or lidocaine. Results In both thoracic and lumbar spinal cord segments, Ca2+ concentratio ns 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 f rom 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) prot ein, respectively, in the thoracic segment and 222, 229 and 176 ng mg(-1) p rotein vs, control 43 ng mg(-1) protein, respectively, in the lumbar segmen t). Lidocaine injection also produced a significant increase in intracellul ar Ca2+ in the thoracic and lumbar spinal cord segments (69, 64 and 53 ng m g(-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 int racellular 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 intracellul ar electrolyte homeostasis in spinal cord neurones of experimental rats. A possible common mechanism of action via Ca2+ ion channels is discussed.