The effects of nickel on contraction and membrane current in isolated rat myocytes.

Depolarization of isolated myocytes for several seconds produces a maintained, tonic component of tension. We have found that this is abolished by 5 mM-Ni2+. Furthermore if Ni2+ is applied after the tonic contraction has developed then its relaxation is prevented. These results are consistent with the hypothesis that Ni2+ inhibits Na+-Ca2+ exchange. Finally, also consistent with an inhibition of Na+-Ca2+ exchange, Ni2+ abolishes the transient inward current while having no effect on the underlying change of [Ca2+]i.