CHARACTERIZATION OF A VOLTAGE-DEPENDENT L-TYPE CALCIUM-CHANNEL FROM RABBIT AND TURTLE BRAIN

The binding of [H-3]nitrendipine to membrane preparation from turtle a nd rabbit brain was studied. A single population of [H-3]nitrendipine binding sites was detected in both species. [H-3]nitrendipine bound wi th high affinity to brain membrane from both rabbit and turtle, reveal ing a significant population of binding sites (K-D values of 0.55 +/- 0.05 nM and 0.56 +/- 0.04 nM and B-max values of 122 +/- 11 and 275 +/ - 18 fmol/mg of protein, respectively). Displacement studies showed a similar order of potency of various unlabeled ligands against [H-3]nit rendipine both in rabbit or in turtle: nitrendipine > nifedipine great er than or equal to nicardipine much greater than verapamil > diltiaze m. Our results show that a two fold increment of [3H]nitrendipine bind ing sites exists in the turtle brain respect to the rabbit.