THE STRETCH-ACTIVATED ION-CHANNEL BLOCKER GADOLINIUM ALSO BLOCKS L-TYPE CALCIUM CHANNELS IN ISOLATED VENTRICULAR MYOCYTES OF THE GUINEA-PIG

We show that gadolinium (Gd3(+)) is a potent calcium channel blocker i n guinea-pig isolated ventricular myocytes. A dose-dependent inhibitio n of I-CaL. was found with an EC(50) of 1.4 mu M and a complete inhibi tion at 10 mu M Gd3(+). When compared with Cd2+, it appeared that the blockade of I-CaL. is a complex phenomenon probably involving more tha n one sitphenomenon probably involving more than one site of interacti on (a Hill coefficient of 1.6 was found for Gd3+ vs. 1.0 for Cd2+). It is concluded that Gd3+ ions completely block I-CaL. at concentrations used to block stretch-activated channels (SAC), rendering its use as a specific SAC inhibitor problematic.