Résumé
Using the whole-cell configuration of the patch-clamp technique, we studied the incomplete recovery of the high voltage-activated calcium current (ICa,L) from a complete blockade by 10 microM gadolinium. The study was performed on isolated guinea-pig ventricular myocytes. ICa,L recovery depended on the duration of application of Gd3+: for a mean application time of 1.63 +/- 0.45 min, a recovery to 67 +/- 22% of the initial current amplitude (n = 12 cells) was observed; when the application lasted 5.1 +/- 1.2 min ICa,L recovered to 27 +/- 13% (n = 14 cells). The partial recovery of ICa,L was accompanied by a slowing of the inactivation phase of the current. IF, during the incomplete recovery, cells were exposed to a solution containing 330 microM of an orthophosphate salt, such as NaH2PO4 or KH2PO4, the current amplitude increased to 80 +/- 13% of the initial current (n = 10 cells) in a reversible manner. However, the slowing of the inactivation phase was maintained. Our results show that the partial recovery of ICa,L from blockade by gadolinium is due to an interaction of the blocker with an extracellular part of the channel, possibly one involved in voltage-dependent inactivation.