[A voltage-clamp study on voltage-gated calcium channels translated in Xenopus oocytes by rat brain mRNA]

Voltage-gated calcium channels, expressed in Xenopus oocytes after injection of rat brain mRNA, were studied by using voltage-clamp technique. The properties of the calcium channels were characterized by barium current (IBa) passed through the channels. All oocytes used in this study were taken from five identified donors. Endogenous voltage--activated barium current measured in most oocytes from these donors were not detectable, or smaller than 15 nA, mRNA was extracted from the whole brains of 10 day postnatal rats and microinjected into the oocytes. IBa increased gradually during five days after mRNA injection. The maximum amplitude of the expressed voltage-activated barium current was usually larger than one hundred of nA on the third day after mRNA injection. In comparison, the expression of voltage-activated barium current was hardly detectable in oocytes injected by mRNA extracted from brains of embryonic rats. The voltage-dependence of activation and inactivation pharmacology of IBa were studied. It was found that IBa was inhibited potently by lanthanide cations (La+3,Nd+3,Sm+3,Eu+3,Gd+3,Dy+3,Er+3) at mumol/L concentration level. L-type calcium channel ligands, nifedipine and Bay K 8644 inhibited IBa at 100 mumol/L, while another dihydropyridine ligand (+/-) nimodipine enhanced IBa at the same concentration.