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Endothelin-1 inhibits L-type Ca currents enhanced by isoproterenol in guinea-pig ventricular myocytes
1The 3rd Department of Internal Medicine, Faculty of Medicine, Kyoto University, Japan.
Insights
Endothelin-1 (ET-1) inhibits L-type calcium currents (ICa,L) in guinea-pig heart cells. This action occurs via ETA receptors and pertussis toxin-sensitive G-proteins, impacting cardiac function.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- Cellular Electrophysiology
Background:
- Endothelin-1 (ET-1) is a potent vasoconstrictor peptide.
- L-type calcium currents (ICa,L) are crucial for cardiac contractility.
- The precise role of ET-1 in regulating cardiac ion channels requires further elucidation.
Purpose of the Study:
- To investigate the effect of ET-1 on ICa,L in guinea-pig ventricular myocytes.
- To determine the receptor subtype and signaling pathway involved in ET-1's action on ICa,L.
- To understand how ET-1 modulates ISO- and histamine-stimulated ICa,L.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to record ICa,L in isolated guinea-pig ventricular myocytes.
- Experiments were conducted at physiological temperature (36-37°C).
- Pharmacological agents including ET-1, isoproterenol (ISO), BQ-123, histamine, and pertussis toxin (PTX) were utilized.
Main Results:
- ET-1 (≥10 nM) suppressed basal ICa,L.
- ET-1 concentration-dependently inhibited ISO-enhanced ICa,L with an IC50 of 168 pM.
- The inhibitory effect of ET-1 was blocked by the ETA receptor antagonist BQ-123.
- ET-1 also suppressed histamine-enhanced ICa,L but not cAMP-potentiated ICa,L.
- PTX pre-treatment abolished the inhibitory action of ET-1.
Conclusions:
- Subnanomolar ET-1 inhibits ICa,L through ETA receptor stimulation.
- The inhibitory pathway involves PTX-sensitive G-proteins.
- ET-1 modulates cardiac calcium channel activity, suggesting a role in cardiac regulation beyond vasoconstriction.
Abstract:
To investigate the action of endothelin-1 (ET-1) on L-type Ca currents (ICa,L) in guinea-pig ventricular cells, whole-cell currents were recorded at approximately 36-37 degrees C in enzymatically isolated myocytes. ET-1 (> or =10 nM) suppressed the basal ICa,L to 79+/-8% of control at 20 nM. Bath application of isoproterenol (ISO; 10 nM) enhanced ICa,L to 192+/-28% with about a -10-mV shift of its relationship with membrane potential. ET-1 concentration dependently inhibited this ISO-enhanced ICa,L with a half-maximally inhibitory concentration (IC50) of 168 pM. The inhibitory actions of ET-1 were antagonised by BQ-123 (300 nM), cyclo(D-Asp-L-Pro-D-Val-L-Leu-D-Trp), a specific ETA receptor antagonist. Histamine-enhanced ICa,L was also suppressed by ET-1, but ICa, L potentiated by internal adenosine 3',5'-cyclic monophosphate (cAMP) was unaffected. Preincubation of myocytes with pertussis toxin (PTX, at 5 microgram/ml for >60 min at 36 degrees C) completely occluded the ET-1 action. Thus, stimulation of ETA receptors by subnanomolar ET-1 inhibits ICa,L via PTX-sensitive G-proteins.