Key Points
- To examine whether binding of the dihydropyridine calcium channel blocker [3H]nitrendipine to isolated rat cardiac myocytes depends on membrane voltage.
- Isolated calcium-tolerant cardiac myocytes enzymatically dispersed from adult male Wistar rats were incubated in physiological (5.6 mM) or depolarizing (50 mM) extracellular potassium buffers.
- Binding kinetics and saturation of [3H]nitrendipine were measured alongside competition assays using unlabeled nitrendipine, nifedipine, verapamil, and diltiazem.
- Receptor density responses were evaluated across varying potassium concentrations (2.4–54.1 mM), with aconitine treatment (1–30 micrograms/ml), and in dead or digitonin-permeabilized myocytes.
- Depolarization in 50 mM potassium buffer roughly doubled maximum receptor density (Bmax) from 10.8 +/- 1.3 to 25.6 +/- 3.7 fmol/mg wet weight without altering dissociation constant KD (587 +/- 50 pM vs. 661 +/- 77 pM).
- Increasing extracellular potassium from 2.4 to 54.1 mM gradually increased binding sites by 115% rapidly and reversibly, while aconitine increased binding sites by 58%.
- No potassium- or aconitine-induced changes in binding sites occurred in dead or digitonin-treated myocytes.
Structured PICO
PPopulationIsolated calcium tolerant cardiac myocytes dissociated by enzymatic dispersion from adult male Wistar rats
IInterventionMembrane depolarization induced by high extracellular potassium (up to 54.1 mM) or aconitine (1-30 micrograms/ml)
CComparatorNormal extracellular potassium buffer (5.6 mM) or dead/digitonin-treated myocytes
OOutcomeBinding of [3H]nitrendipine (affinity/KD and maximum receptor density/Bmax)surrogate
In viable rat cardiac myocytes, the density of dihydropyridine calcium antagonist binding sites is voltage-dependent and increases with membrane depolarization.