Voltage-dependent nitrendipine binding to cardiac sarcolemmal vesicles

Area of Science:

• Cardiovascular Physiology
• Membrane Biophysics
• Pharmacology

Background:

• Cardiac sarcolemmal vesicles are crucial for studying ion channel function.
• Calcium channel antagonists play a vital role in cardiovascular medicine.
• Membrane potential is a key determinant of ion channel activity.

Purpose of the Study:

• To investigate the effect of membrane potential on the binding of [3H]nitrendipine to bovine cardiac sarcolemmal vesicles.
• To determine if changes in membrane potential alter the affinity or number of binding sites for calcium channel antagonists.

Main Methods:

• Purified bovine cardiac sarcolemmal vesicles were used.
• Membrane potential was manipulated by varying external potassium concentrations and using N-methyl-D-glucamine or choline as substitutes.
• [3H]tetraphenylphosphonium was employed to quantify membrane potential.
• Equilibrium binding studies were performed using [3H]nitrendipine.

Main Results:

• Depolarized membrane potentials (0 mV) showed a significant increase (24.7% with NMG, 19.0% with choline) in high-affinity [3H]nitrendipine binding sites compared to hyperpolarized potentials (-40 to -50 mV).
• The dissociation constant (Kd) for [3H]nitrendipine binding remained unchanged across different membrane potentials.
• Graded changes in [3H]nitrendipine binding correlated with changes in membrane potential, supporting its role.

Conclusions:

• Membrane potential directly influences the number of high-affinity binding sites for the calcium channel antagonist [3H]nitrendipine.
• The observed effect is primarily attributed to alterations in membrane potential, not changes in vesicle composition.
• These findings have implications for understanding calcium channel pharmacology in different physiological states.