Gadolinium inhibits Na+-Ca2+ exchanger current in guinea-pig isolated ventricular myocytes

The trivalent cation, gadolinium (Gd3+) is commonly used to inhibit stretch -activated channels. In this report, we show that Gd3+ also inhibits ionic current (I-NaCa), carried by the Na+-Ca2+ exchanger protein. Under selectiv e recording conditions, Gd3+; inhibited both outward and inward I-NaCa from guinea-pig isolated ventricular myocytes in a dose-dependent manner, with half-maximal inhibition concentrations (IC50) of 30.0 +/- 4.0 mu M at + 60 mV (Hill-coefficient, h = 1.04 +/- 0.13) and 20.0 +/- 2.7 mu M at -100 mV ( h=1.13+/-0.16), respectively (P>0.05, n=5-9). Thus, inhibition was not volt age-dependent. The time from Gd3+ application to steady-state effect was sl ow compared to the divalent blocker Ni2+. The slow time course appeared to reflect gradual Gd3+ accumulation at its binding site on the exchanger, rat her than a use-dependent blocking mechanism. This study indicates that for experiments in which Gd3+ is used, its inhibitory effect on I-NaCa Should b e taken into account.