Reversible Dihydropyridine Isothiocyanate Binding to Brain Calcium Channels

Voltage-dependent calcium channels from ileal smooth muscle can be affinity-labeled with a [3H]dihydropyridine isothiocyanate radioligand. We examined the binding of this agent to brain membranes, to compare the properties of calcium channel drug binding sites in brain with those previously described in ileum. In brain, the [3H]dihydropyridine isothiocyanate labels sites that correspond in number and pharmacologic characteristics to binding sites for the classic calcium entry blocker, [3H]nitrendipine. However, in contrast to the covalent nature of dihydropyridine isothiocyanate binding in ileum, brain calcium channels are labeled reversibly. This difference in binding properties may reflect structural variations in voltage-dependent calcium channels in different tissues.