tokens: It decreased by 16 + / - 3 % by lowering [ Na ] o to 78 mM ( LNa ) , 23 + / - 2 % by lowering simultaneously [ Na ] o to 78 mM and [ Ca ] o to 0 . 675 mM ( LNa + LCa ) and 31 + / - 5 % by lowering [ Na ] o to 78 mM plus increasing [ Ca ] o to 3 . 6 mM ( LNa + HCa ) .