Nitrendipine block of cardiac calcium channels: high-affinity binding to the inactivated state

Area of Science:

• Cardiovascular Physiology
• Molecular Pharmacology
• Ion Channel Biophysics

Background:

• Dihydropyridine drugs, like nitrendipine, are known to affect calcium (Ca2+) channel activity.
• Understanding the precise binding states of drugs to ion channels is crucial for pharmacology.
• Previous studies indicated high-affinity binding of [3H]nitrendipine to tissue membranes.

Purpose of the Study:

• To investigate the mechanism of calcium (Ca2+) current block by nitrendipine in canine ventricular cells.
• To determine the binding affinity of nitrendipine to different states of the Ca2+ channel.
• To correlate drug binding with known high-affinity radioligand binding sites.

Main Methods:

• Whole-cell patch clamp technique applied to single canine ventricular cells.
• Measurement of Ca2+ currents under varying membrane potentials (depolarized and hyperpolarized).
• Analysis of nitrendipine concentration-dependent block and apparent dissociation constants (Kd).

Main Results:

• Nitrendipine exhibited potent block of Ca2+ currents at depolarized potentials (70% inactivated state) with a Kd of 0.36 nM.
• Block was significantly less potent at hyperpolarized potentials (resting state) with a Kd of approximately 700 nM.
• Observed binding kinetics and affinity align with high-affinity [3H]nitrendipine binding to membrane fragments.

Conclusions:

• Nitrendipine preferentially binds to the inactivated state of the Ca2+ channel.
• The high-affinity [3H]nitrendipine binding site likely represents the inactivated state of the Ca2+ channel.
• This provides a mechanistic link between drug action and radioligand binding studies.