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Receptor-mediated effects of endothelin on the L-type Ca++ current in ventricular cardiomyocytes
E J Kelso1, J P Spiers, B J McDermott
1Department of Therapeutics and Pharmacology, The Queen's University of Belfast, Belfast, Northern Ireland.
Abstract:
The purpose of this study was to establish whether specific receptor subtypes are responsible for mediating the effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on the L-type calcium current (ICa) using a number of receptor-selective antagonists, including PD155080 (ETA), BQ-788, RES-701 and IRL-1038 (ETB) and the ETA/ETB receptor-non-selective antagonist PD145065. Ventricular cardiomyocytes were isolated from adult New Zealand White rabbits using Langendorff perfusion with collagenase. ICa was recorded using a whole-cell patch-clamp technique. ET-1 decreased, whereas ET-3 increased, ICa at equimolar concentrations of 10 nM. The decrease in ICa produced by ET-1 was completely blocked by PD155080 and PD145065 (1 and 10 microM); however, ICa was increased upon washout of PD155080. Although the decrease in ICa produced by ET-1 was partially blocked by BQ-788 (1 and 10 microM), ET-1 in combination with either RES-701 (1 and 10 microM) or IRL-1038 (1 microM) produced a decrease in ICa similar to that produced by ET-1 alone. The increase in ICa by ET-3 was completely abolished by either BQ-788 or IRL-1038 (1 microM). These data indicate that the decrease in ICa produced by ET-1 in rabbit ventricular cardiomyocytes is mediated by the ETA receptor subtype, because PD155080 completely inhibited this response. The ETB receptor-selective antagonists RES-701 and IRL-1038 did not alter the decrease in current produced by ET-1, although the response was partially sensitive to BQ-788, which may lack receptor-subtype selectivity in these cells. In contrast, the increase in ICa produced by ET-3 was mediated by the ETB receptor subtype, because BQ-788 and IRL-1038 abolished this response.
Insights
Endothelin-1 (ET-1) decreases L-type calcium current (ICa) via ETA receptors, while endothelin-3 (ET-3) increases ICa through ETB receptors in rabbit heart cells. This clarifies endothelin signaling pathways in cardiac function.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- Ion Channel Function
Background:
- Endothelin-1 (ET-1) and endothelin-3 (ET-3) are vasoactive peptides with known roles in cardiovascular regulation.
- The specific receptor subtypes mediating the effects of ET-1 and ET-3 on cardiac ion currents remain incompletely understood.
- L-type calcium current (ICa) is critical for cardiomyocyte excitation-contraction coupling.
Purpose of the Study:
- To elucidate the specific endothelin receptor subtypes (ETA and ETB) responsible for mediating the effects of ET-1 and ET-3 on ICa in rabbit ventricular cardiomyocytes.
- To utilize a panel of selective receptor antagonists to differentiate the roles of ETA and ETB receptors.
Main Methods:
- Isolation of adult New Zealand White rabbit ventricular cardiomyocytes.
- Whole-cell patch-clamp technique to record L-type calcium current (ICa).
- Application of ET-1 and ET-3 at equimolar concentrations (10 nM) in the presence of receptor-selective antagonists (PD155080 for ETA; BQ-788, RES-701, IRL-1038 for ETB) and a non-selective antagonist (PD145065).
Main Results:
- ET-1 significantly decreased ICa, an effect completely blocked by the ETA antagonist PD155080 and the non-selective antagonist PD145065.
- ET-3 significantly increased ICa, an effect completely abolished by the ETB antagonists BQ-788 and IRL-1038.
- ETB-selective antagonists showed minimal effect on ET-1-induced ICa decrease, while BQ-788 exhibited partial blockade, suggesting potential lack of subtype selectivity in this context.
Conclusions:
- The inhibitory effect of ET-1 on ICa in rabbit ventricular cardiomyocytes is predominantly mediated by the ETA receptor subtype.
- The stimulatory effect of ET-3 on ICa in these cells is primarily mediated by the ETB receptor subtype.
- These findings delineate the distinct roles of ETA and ETB receptors in modulating cardiac calcium channel activity by different endothelin peptides.