Subunit Architecture & Binding Allostery
his specific subunit of the L-type voltage-gated calcium channel forms the ion-conducting pore, acts as the voltage sensor, and carries the drug receptor sites for all three CCB classes.
What is the $\alpha_1$ subunit?
Immediate-release formulations of this 1st-generation prototype dihydropyridine can cause a precipitous drop in blood pressure that triggers reflex tachycardia, worsening angina and increasing mortality risk.
What is Nifedipine?
Verapamil is classified chemically as a phenylalkylamine, whereas diltiazem belongs to this distinct chemical class.
What is a Benzothiazepine?
Dihydropyridine CCBs frequently cause peripheral and pedal edema because they dilate peripheral arterioles without dilating these vascular structures, overloading capillaries and expelling fluid into surrounding tissue.
What are veins (venules)?
Unlike the transmembrane accessory subunits, this CCB channel subunit is entirely cytoplasmic and is essential for trafficking the $\alpha_1$ subunit to the cell membrane.
What is the $\beta$ subunit?1
This 3rd-generation dihydropyridine possesses an exceptionally long elimination half-life of 30 to 50 hours, allowing for once-daily dosing without inducing reflex tachycardia.
What is Amlodipine (Norvasc)?
Non-dihydropyridines function as antiarrhythmic agents primarily by blocking slow inward calcium channels to decrease conduction velocity during Phase 0 in these cardiac nodal regions
What are the Sinoatrial (SA) and Atrioventricular (AV) nodes?
Except for clevidipine (which undergoes rapid esterase hydrolysis), all CCBs are major substrates of this hepatic enzyme and must not be taken with grapefruit juice.
What is CYP3A4?
While the dihydropyridine and benzothiazepine binding sites are accessed from the extracellular side of the membrane, verapamil's phenylalkylamine site must be accessed from this location.
What is the intracellular side of the channel?
Due to its high lipid solubility and pronounced vasodilation of cerebral vasculature, this 2nd-generation dihydropyridine is indicated for the prophylactic treatment of cerebral vasospasm in subarachnoid hemorrhage.
What is Nimodipine (Nimotop)?
Extensive first-pass CYP3A4 hepatic metabolism reduces the oral bioavailability of verapamil to ~40%, yielding this primary active metabolite that retains 20% of the parent drug's activity
What is Norverapamil?
In addition to headache and peripheral edema, verapamil is particularly notorious among calcium channel blockers for causing this specific gastrointestinal adverse effect
What is constipation?
Verapamil and diltiazem exhibit negative allosteric coupling toward each other, but diltiazem exhibits this type of allosteric coupling toward dihydropyridine (e.g., amlodipine) binding.
What is positive allosteric coupling (enhancing DHP binding)?
Formulated as an IV oil-in-water emulsion containing soybean oil and egg yolk phospholipids, this ultra-short acting agent has a 2-minute onset and a 15-minute duration of action for hypertensive crises
What is Clevidipine (Cleviprex)?
Because verapamil exerts prominent negative inotropic and negative chronotropic effects on the heart, it is strictly contraindicated in patients with hypotension or this structural cardiac deficit
What is severe left ventricular dysfunction (or severe heart failure)?
Because diltiazem and verapamil inhibit CYP3A4 and raise statin concentrations, patients taking them should switch to non-CYP3A4-metabolized statins such as pravastatin, rosuvastatin, or this drug.
What is Pitavastatin?
In vascular smooth muscle, calcium entry activates myosin light-chain kinase; in cardiac myocytes, calcium entry through L-type channels triggers additional calcium release from the sarcoplasmic reticulum through these specific receptors.
What are Ryanodine receptors (RyR)?
This 3rd-generation dihydropyridine is explicitly highlighted as being safe to use if a DHP CCB is required to lower blood pressure in patients with heart failure with reduced ejection fraction (HFrEF)
What is Amlodipine?
Verapamil and diltiazem are rarely prescribed together because their mutual negative allosteric coupling and additive nodal suppression create a high risk for this severe cardiac conduction defect.
What is additive AV-node block (or severe bradycardia)?
In addition to known allergies to soy or egg products, intravenous clevidipine is contraindicated in patients with preexisting defects in this physiological metabolic pathway.
What is lipid metabolism (e.g., severe hyperlipidemia)?