In vivo quantification of myocardial dihydropyridine binding sites: a PET study in dogs

Abnormalities in myocardial L-type Ca(2+) channel abundance and function have been described in cardiac hypertrophy and failure. In vivo quantification of the density of these channels using PET and an adequate ligand would provide new insights into cardiac disease.

The dihydropyridine L-type Ca(2+) channel antagonist S12968 (3-ethyl 5-methyl (-)-2-[(2-(2-aminoethoxy)ethoxy)methyl]-4-(2,3-dichlorophenyl)-6-methyl-1,4-dihydropyridine-3,5-dicarboxylate) was labeled with (11)C and injected in various amounts (5-23 nmol), 20 or 30 min apart, into dogs. This protocol allowed a separate evaluation of the density of binding sites (B(max)) as well as association and dissociation rate constants. The parameters were calculated using a nonlinear mathematic model.

Using the multiinjection approach, a complete model describing interactions between S12968 and the dihydropyridine binding sites was obtained. B(max) was found to be 19.2 +/- 3.3 pmol x mL(-1) of tissue. Association and dissociation constants (estimated by K(on)/VR and K(d)VR, respectively) were found to be 0.015 +/- 0.01 mL x pmol(-1) x min(-1) and 4.2 +/- 2.2 nmol x mL(-1), respectively.

The present data suggest that it is possible to measure myocardial dihydropyridine binding site density with a single radiosynthesis and a simple PET protocol that is not time consuming (75 min for the total examination, including transmission and emission scans). This methodology can be useful to investigate human cardiac disease in vivo.