title: Magnesium sulfate suppresses L-type calcium currents on the basilar artery smooth muscle cells in rabbits.
abstract: OBJECTIVE
  Although magnesium is a well-known treatment for vasospasm following subarachnoid hemorrhage, its mechanism of action for cerebral vascular relaxation is not clear. In addition, it is known that L-type calcium (Ca(2+)) channels play a pivotal  role in smooth muscle contraction. To investigate the role of L-type Ca(2+) channels in the magnesium-induced relaxation of basilar smooth muscle cells, we examined the effect of magnesium sulfate on L-type Ca(2+) currents using freshly isolated smooth muscle cells from rabbit  basilar arteries.
  
  
  METHODS
  Rabbits were anesthetized with ketamine (50 mg/kg) with xylazine (25 mg/kg) and exsanguinated. Smooth muscle cells were isolated from rabbit basilar arteries by enzyme treatment. Cells were stored at 4°C before use. Whole-cell patch clamp technique was  used to identify L-type Ca(2+) currents, using the potassium channel blocker, cesium chloride, and nimodipine and Bay K8644 as a blocker and activator of L-type Ca(2+) channels, respectively.
  
  
  RESULTS
  Inward currents induced by step pulses were significantly reduced  by nimodipine (n = 5, P<0·05) and increased by Bay K8644 (n = 5, P<0·05). The L-type Ca(2+) currents (122±14·0 pA, n = 12) were significantly reduced by the application of 5 mM magnesium  sulfate (28±4 pA, n = 12, P<0·05). The inward currents enhanced by Bay K8644 were further suppressed by the application of magnesium sulfate.
  
  
  CONCLUSIONS
  These results demonstrate that L-type Ca(2+) channels are functionally expressed  in rabbit basilar smooth muscle cells and suggest that L-type Ca(2+) channels may play a pivotal role for magnesium-induced relaxation.
authors.affiliation: Department of Pediatrics and Research Institute of Clinical Medicine, Chonbuk National University Hospital and School of Medicine, Jeonju, Korea.
authors.forename: Naveen
authors.initials: N
authors.lastname: Sharma
authors.forename: Dong Hyu
authors.initials: DH
authors.lastname: Cho
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Janardhan Prasad
authors.initials: JP
authors.lastname: Bhattarai
authors.forename: Pyoung Han
authors.initials: PH
authors.lastname: Hwang
authors.forename: Seong Kyu
authors.initials: SK
authors.lastname: Han
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D001488:Basilar Artery / Q000187:drug effects*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D008278:Magnesium Sulfate / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D000927:Anticonvulsants; D020746:Calcium Channels, L-Type; D008278:Magnesium Sulfate