Calcium Transport and Calcium ATPase — MCQs
What is the PRIMARY mechanism by which the Na+-Ca2+ exchanger functions in cardiac muscle cells?
Equilibrium potential of calcium is
Calcium does not bind to
In response to changes in Ca2+ concentration, which of the following Ca2+ binding proteins can modify the activity of many enzymes & proteins?
Which of the following is the best inotrope agent for use in right heart failure secondary to pulmonary hypertension?
The effect seen due to decreased serum calcium concentration is
Statement 1 - A 59-year-old patient presents with flaccid bullae. Histopathology shows a suprabasal acantholytic split. Statement 2 - The row of tombstones appearance is diagnostic of Pemphigus vulgaris.
Which of the following ion plays a role in exocytosis?
Hyperkalemia management includes all except:
Preferred drug for the treatment of ventricular tachycardia is
Calcium Transport and Calcium ATPase Indian Medical PG Practice Questions and MCQs
Question 1: What is the PRIMARY mechanism by which the Na+-Ca2+ exchanger functions in cardiac muscle cells?
- A. Na+-Ca2+ exchanger requires ATP directly
- B. Na+-Ca2+ exchanger acts to remove Ca2+ from heart muscle cells (Correct Answer)
- C. The Na+-Ca2+ exchanger operates in reverse mode during normal cardiac contraction
- D. The Na+-Ca2+ exchanger primarily moves Ca2+ into cardiac muscle cells during systole
Explanation: ***Na+-Ca2+ exchanger acts to remove Ca2+ from heart muscle cells.*** - The primary function of the **Na+-Ca2+ exchanger (NCX)** in cardiac muscle is to **extrude calcium from the cell** into the extracellular space. - It uses the electrochemical gradient of **sodium (Na+)** which flows into the cell, to power the removal of **calcium (Ca2+)** from the cell, contributing to muscle relaxation during diastole. *The Na+-Ca2+ exchanger operates in reverse mode during normal cardiac contraction* - While it can theoretically operate in reverse, its **primary physiological role** during normal cardiac contraction is forward mode (Ca2+ extrusion). - Reverse mode operation (Ca2+ influx) is typically seen under specific conditions, such as **pathological states** or severely altered intracellular Na+ concentrations. *Na+-Ca2+ exchanger requires ATP directly* - The **Na+-Ca2+ exchanger** is a **secondary active transporter** and does not directly use ATP. - Its energy comes from the **electrochemical gradient of Na+**, which is maintained by the **Na+/K+-ATPase** (primary active transport, which *does* use ATP). *The Na+-Ca2+ exchanger primarily moves Ca2+ into cardiac muscle cells during systole.* - Moving **Ca2+ into the cell** during systole would primarily be the role of **L-type calcium channels** on the sarcolemma. - The NCX's main role is to **reduce intracellular Ca2+** after contraction, facilitating relaxation during diastole.
Question 2: Equilibrium potential of calcium is
- A. +130mV (Correct Answer)
- B. -32mV
- C. +65mV
- D. -95mV
Explanation: ***+130mV*** - The **equilibrium potential** for an ion is the **membrane potential** at which the net movement of that ion across the membrane is zero, even if there is a concentration gradient. - Due to the significantly higher extracellular concentration of **calcium ions (Ca2+)** relative to the intracellular concentration, a large positive membrane potential is required to prevent Ca2+ influx. *-32mV* - This value does not represent the typical **equilibrium potential** for any major physiological ion like sodium, potassium, chloride, or calcium in mammalian cells. - Equilibrium potentials are highly dependent on the **concentration gradients** of the specific ion. *+65mV* - This value is close to the typical **equilibrium potential for sodium (Na+)**, which is approximately +60 to +70 mV in many cells, due to its outward concentration gradient. - **Calcium's equilibrium potential** is much more positive than sodium's due to its larger concentration gradient and its divalent charge. *-95mV* - This value is close to the typical **equilibrium potential for potassium (K+)**, which is approximately -90 to -95 mV, reflecting the movement of potassium out of the cell. - The **equilibrium potential for calcium** is highly positive, whereas this negative value suggests an inward current for a positively charged ion.
Question 3: Calcium does not bind to
- A. Troponin
- B. Calmodulin
- C. Tropomyosin (Correct Answer)
- D. None of the options
Explanation: ***Tropomyosin*** - **Tropomyosin** is a protein that winds around **actin filaments** and, in relaxed muscle, blocks the **myosin-binding sites** on actin, preventing contraction. - Calcium does **not directly bind** to tropomyosin; rather, its binding to **troponin** causes a conformational change that moves tropomyosin away from the binding sites. - **This is the correct answer** because tropomyosin lacks calcium-binding sites. *Incorrect: Troponin* - **Troponin** is a complex of three proteins (**troponin I, T, and C**) that is crucial for muscle contraction. - **Troponin C** is the specific subunit that **binds calcium ions**, initiating the cascade of events leading to muscle contraction. - This option is incorrect because troponin DOES bind calcium. *Incorrect: Calmodulin* - **Calmodulin** is a ubiquitous **calcium-binding messenger protein** expressed in all eukaryotic cells. - It mediates many crucial cellular processes by interacting with and regulating various protein targets (e.g., kinases, phosphatases) when it **binds to calcium ions**. - This option is incorrect because calmodulin DOES bind calcium. *Incorrect: None of the options* - This option would suggest that all the listed proteins bind calcium. - Since **tropomyosin does NOT bind calcium**, this option is incorrect.
Question 4: In response to changes in Ca2+ concentration, which of the following Ca2+ binding proteins can modify the activity of many enzymes & proteins?
- A. Collagen
- B. Calmodulin (Correct Answer)
- C. Kinesin
- D. Elastin
Explanation: ***Calmodulin*** - **Calmodulin** is a highly conserved, 148-amino acid protein with four **calcium-binding EF-hand motifs**. - Upon binding to **calcium ions (Ca2+)**, it undergoes a conformational change that enables it to interact with and regulate the activity of a wide variety of enzymes and proteins, including **kinases, phosphatases, and ion channels**, mediating many Ca2+-dependent cellular processes. *Collagen* - **Collagen** is a major structural protein in the extracellular matrix, providing **tensile strength** to tissues. - Its primary function is structural support, rather than acting as a calcium-sensing regulatory protein for enzyme activity. *Kinesin* - **Kinesin** is a **motor protein** involved in intracellular transport, moving cargo along microtubules. - While its activity can be modulated, it is not primarily known as a calcium-binding protein that directly regulates a broad range of enzymes in response to calcium concentration changes. *Elastin* - **Elastin** is a highly elastic protein found in connective tissue, allowing tissues to **recoil after stretching**. - Like collagen, its main role is structural, contributing to the elasticity of tissues, rather than signaling or enzyme regulation via calcium binding.
Question 5: Which of the following is the best inotrope agent for use in right heart failure secondary to pulmonary hypertension?
- A. Milrinone (Correct Answer)
- B. Dobutamine
- C. Digoxin
- D. Dopamine
Explanation: ***Milrinone*** - Milrinone is a **phosphodiesterase-3 inhibitor** that increases myocardial contractility and causes **pulmonary and systemic vasodilation**. - Its vasodilatory effect is particularly beneficial in **pulmonary hypertension** as it can help reduce **pulmonary vascular resistance (PVR)**, a critical factor in right heart failure. - The combination of **positive inotropy** and **selective pulmonary vasodilation** makes it the optimal choice for right ventricular failure secondary to pulmonary hypertension. *Dobutamine* - Dobutamine is a **beta-1 agonist** that primarily increases myocardial contractility with some beta-2 mediated vasodilation. - While it improves cardiac output, its lesser effect on **pulmonary vascular resistance** compared to milrinone makes it less ideal for right heart failure specifically complicated by pulmonary hypertension. *Digoxin* - Digoxin is a **cardiac glycoside** that increases contractility but has a slow onset of action and a narrow therapeutic window, making it less suitable for acute management. - It does not significantly reduce **pulmonary vascular resistance** and is primarily used for chronic heart failure or rate control in atrial fibrillation. *Dopamine* - Dopamine is a **catecholamine** with dose-dependent effects: at moderate doses (5-10 mcg/kg/min), it acts as a **beta-1 agonist** providing inotropic support. - However, at higher doses it causes **alpha-adrenergic vasoconstriction** which can **increase pulmonary vascular resistance**, potentially worsening right heart failure in pulmonary hypertension. - Unlike milrinone, it lacks specific pulmonary vasodilatory properties beneficial for reducing RV afterload.
Question 6: The effect seen due to decreased serum calcium concentration is
- A. Depression of nervous system
- B. Excitability of muscle (Correct Answer)
- C. Increased renal absorption
- D. Relaxation of muscle
Explanation: ***Excitability of the muscle*** - A decrease in serum calcium concentration (**hypocalcemia**) reduces the threshold potential for sodium channels, making nerve and muscle cells **more excitable**. - This increased excitability can lead to symptoms like **tetany**, muscle spasms, and even convulsions. *Depression of Nervous system* - This is typically seen with **hypercalcemia** (increased serum calcium), where elevated calcium levels stabilize nerve membranes, making them less excitable. - **Hypocalcemia**, conversely, leads to neuronal hyperexcitability, not depression. *Increase the renal absorption* - Renal calcium reabsorption is primarily regulated by **parathyroid hormone (PTH)**. Low serum calcium stimulates PTH release, which *increases* renal calcium reabsorption to restore calcium levels. - This is a *physiological response* to hypocalcemia, not an *effect* of hypocalcemia on neural or muscular function. *Relaxation of muscle* - Muscle relaxation requires ATP and the re-sequestration of calcium into the sarcoplasmic reticulum, and is not a direct consequence of low extracellular calcium. - Instead, **hypocalcemia** causes increased muscle **contraction** and spasms due to enhanced neuromuscular excitability.
Question 7: Statement 1 - A 59-year-old patient presents with flaccid bullae. Histopathology shows a suprabasal acantholytic split. Statement 2 - The row of tombstones appearance is diagnostic of Pemphigus vulgaris.
- A. Statements 1 & 2 are correct, 2 is not explaining 1 (Correct Answer)
- B. Statements 1 and 2 are correct and 2 is the correct explanation for 1
- C. Statements 1 and 2 are incorrect
- D. Statement 1 is incorrect
Explanation: ***Correct: Statements 1 & 2 are correct, 2 is not explaining 1*** **Analysis of Statement 1:** - A 59-year-old patient with **flaccid bullae** and **suprabasal acantholytic split** on histopathology is the classic presentation of **Pemphigus vulgaris** - The flaccid (easily ruptured) nature of bullae distinguishes it from tense bullae seen in bullous pemphigoid - The suprabasal location of the split (just above the basal layer) with acantholysis (loss of cell-to-cell adhesion) is pathognomonic - **Statement 1 is CORRECT** ✓ **Analysis of Statement 2:** - The **"row of tombstones" or "tombstone appearance"** is indeed a diagnostic histopathological feature of Pemphigus vulgaris - This appearance results from basal keratinocytes remaining attached to the basement membrane while suprabasal cells separate due to acantholysis - The intact basal cells standing upright resemble a row of tombstones - **Statement 2 is CORRECT** ✓ **Does Statement 2 explain Statement 1?** - Statement 2 describes a **histopathological appearance** (tombstone pattern) that is a **consequence** of the suprabasal split - However, it does NOT explain the **underlying cause** of the flaccid bullae or the suprabasal split - The true explanation involves **IgG autoantibodies against desmoglein 3 (and desmoglein 1)**, which attack intercellular adhesion structures (desmosomes), causing **acantholysis** - Therefore, **Statement 2 does NOT explain Statement 1** ✗ *Incorrect: Statement 2 is the correct explanation for Statement 1* - While both statements describe features of Pemphigus vulgaris, the tombstone appearance is a descriptive finding, not an explanatory mechanism *Incorrect: Statements 1 and 2 are incorrect* - Both statements are medically accurate descriptions of Pemphigus vulgaris features *Incorrect: Statement 1 is incorrect* - Statement 1 correctly describes the cardinal clinical and histopathological features of Pemphigus vulgaris
Question 8: Which of the following ion plays a role in exocytosis?
- A. Potassium
- B. Sodium
- C. Calcium (Correct Answer)
- D. Magnesium
Explanation: ***Calcium*** - **Calcium ions** are crucial for initiating the fusion of **secretory vesicles** with the plasma membrane during **exocytosis**. - An increase in intracellular calcium concentration, often due to an influx from outside the cell, triggers the release of neurotransmitters, hormones, and other substances. *Potassium* - **Potassium ions** are primarily involved in maintaining the **resting membrane potential** and repolarization during action potentials. - While essential for neuronal function, they do not directly trigger the **vesicle fusion** step of exocytosis. *Sodium* - **Sodium ions** are vital for depolarizing the membrane and initiating **action potentials**, as well as for certain co-transport mechanisms. - However, they do not directly bind to proteins involved in **exocytosis** to trigger the release mechanism. *Magnesium* - **Magnesium ions** serve as **cofactors** for many enzymes, including ATPases, and play a role in stabilizing nucleic acids and proteins. - While important for overall cellular function, magnesium does not directly initiate or regulate the **fusion events** of exocytosis.
Question 9: Hyperkalemia management includes all except:
- A. Insulin drip
- B. MgSO4 (Correct Answer)
- C. Salbutamol nebulisation
- D. Calcium gluconate
Explanation: ***MgSO4*** - **Magnesium sulfate (MgSO4)** is primarily used to treat **hypomagnesemia** and certain arrhythmias like **Torsades de Pointes**, and for seizures in preeclampsia. - It does **not have a direct role** in the acute management of hyperkalemia. *Insulin drip* - **Insulin** (often given with glucose) actively drives potassium **into cells**, thereby lowering serum potassium levels [1]. - This is a common and effective temporary measure for **hyperkalemia**, especially in urgent situations. *Salbutamol nebulisation* - **Salbutamol**, a **beta-2 agonist**, stimulates the cellular **Na-K ATPase pump**, leading to a shift of potassium from the extracellular to the intracellular space [1]. - It provides a **rapid, albeit temporary**, reduction in serum potassium levels. *Calcium gluconate* - **Calcium gluconate** does not lower serum potassium levels but rather **stabilizes the cardiac membrane**, protecting the heart from the adverse effects of hyperkalemia [1]. - It is crucial for preventing **life-threatening arrhythmias** in severe hyperkalemia [1].
Question 10: Preferred drug for the treatment of ventricular tachycardia is
- A. Digoxin
- B. Propranolol
- C. Diltiazem
- D. Lignocaine (Correct Answer)
Explanation: ***Lignocaine*** *(Historical Answer for FMGE-2019)* - **Lignocaine** (also known as **lidocaine**) is a **Class IB antiarrhythmic** drug that was historically the preferred treatment for **ventricular tachycardia (VT)**, especially in patients with **ischemic heart disease**. - It works by **blocking sodium channels** in the heart, specifically targeting depolarized or partially depolarized cells, which helps to stabilize the ventricular rhythm. - **⚠️ IMPORTANT UPDATE:** Current guidelines (AHA/ACC 2015 onwards) now recommend **amiodarone as the first-line antiarrhythmic** for hemodynamically stable VT, with lignocaine as a **second-line alternative**. This question reflects the teaching prevalent at the time of FMGE-2019. *Digoxin* - **Digoxin** is a **cardiac glycoside** primarily used for **atrial fibrillation** with rapid ventricular response and **heart failure**. - It is **not the preferred drug** for ventricular tachycardia and can even precipitate arrhythmias in some cases. *Propranolol* - **Propranolol** is a **beta-blocker** (Class II antiarrhythmic) typically used to treat **supraventricular tachycardias**, **hypertension**, and **angina**. - While beta-blockers can have some role in preventing recurrent VT, they are **not the first-line treatment** for acute VT. *Diltiazem* - **Diltiazem** is a **calcium channel blocker** (Class IV antiarrhythmic) primarily used for **supraventricular tachycardias** and to control ventricular rate in **atrial fibrillation**. - It is **not effective** for ventricular tachycardia and may worsen the condition in some cases.
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