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Calcium activation of hyperpolarization response to acetylcholine in coronary endothelial cells
1University of Ottawa Heart Institute, Canada.
Insights
Acetylcholine (ACh) triggers hyperpolarization in guinea pig coronary artery endothelial cells. This response depends on extracellular calcium influx and internal calcium release, modulated by a caffeine-sensitive pool.
Area of Science:
- Cardiovascular Physiology
- Endothelial Cell Biology
- Calcium Signaling
Background:
- Endothelial cells play a crucial role in regulating vascular tone and function.
- Acetylcholine (ACh) is a key neurotransmitter with significant effects on the cardiovascular system.
- Understanding the mechanisms of endothelial cell responses to ACh is vital for cardiovascular health.
Purpose of the Study:
- To investigate the cellular mechanisms underlying the hyperpolarization response to acetylcholine (ACh) in guinea pig coronary artery endothelial cells.
- To elucidate the role of extracellular and intracellular calcium in mediating ACh-induced hyperpolarization.
- To identify the specific calcium stores and signaling pathways involved.
Main Methods:
- Intracellular recording of an intact endothelium preparation from guinea pig coronary artery.
- Application of acetylcholine (ACh) to stimulate endothelial cells.
- Utilizing extracellular calcium depletion and specific calcium antagonists (MnCl2, TMB-8) to probe calcium influx.
- Employing cyclopiazonic acid to inhibit sarcoplasmic reticulum Ca2+ pumps and assess internal calcium stores.
- Investigating the effects of caffeine on hyperpolarization.
Main Results:
- Acetylcholine (ACh) induced a significant hyperpolarization response in endothelial cells.
- This hyperpolarization was dependent on extracellular Ca2+, as evidenced by blockade with MnCl2 and calcium removal.
- The intracellular calcium antagonist TMB-8 abolished the hyperpolarization.
- Cyclopiazonic acid potentiated ACh-induced hyperpolarization but inhibited caffeine-induced hyperpolarization, suggesting distinct calcium pool involvement.
- Findings indicate a dual role of extracellular calcium influx and IP3-sensitive internal store release in ACh-induced hyperpolarization.
Conclusions:
- ACh-induced hyperpolarization in guinea pig coronary artery endothelial cells is mediated by increased cytosolic Ca2+.
- Both extracellular Ca2+ influx and release from intracellular IP3-sensitive stores contribute to this rise in cytosolic Ca2+.
- A caffeine-sensitive calcium pool, modulated by cyclopiazonic acid, plays a role in regulating the cytosolic Ca2+ levels during ACh stimulation.
Abstract:
Hyperpolarization response to acetylcholine (ACh) in endothelial cells was studied by intracellular recording of an intact endothelium preparation of guinea pig coronary artery. The hyperpolarization requires the presence of extracellular Ca2+ and the response was progressively blocked by MnCl2 or by removal of extracellular Ca2+. The intracellular Ca2+ antagonist, 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester hydrochloride (TMB-8, 10 microM), was also effective in abolishing the hyperpolarization. Cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum Ca2+ pump, potentiated the hyperpolarization to ACh but inhibited caffeine-induced hyperpolarization. These findings suggest that ACh-induced hyperpolarization is mediated by an increase in cytosolic Ca2+ due to influx of extracellular Ca2+ and release of Ca2+ from an internal IP3-sensitive store. The rise in cytosolic Ca2+ level was modulated by a caffeine-sensitive pool that is inhibited by cyclopiazonic acid.