Characterization of the endothelin-1-induced regulation of L-type Ca2+ current in rabbit ventricular myocytes.
The effects of endothelin-1 (ET-1) on the L-type Ca2+ current (I(Ca)) and the interaction of ET-1 with beta-adrenoceptor stimulation were investigated in rabbit ventricular myocytes by the whole-cell patch-clamp technique. ET-1 (10(-8) M) had a biphasic effect on I(Ca) (direct effect), causing a transient decrease that was followed by a long-lasting increase which is much smaller than the increase induced by isoprenaline (ISO). The effect of ET-1 on I(Ca) was abolished by a selective ET(A) receptor antagonist, FR139317 (10(-6) M). The increase in I(Ca) induced by ET-1 (10(-8) M) was enhanced by a selective ET(B) receptor antagonist, BQ-788 (10(-6) M), as the transient decrease but not the increase in I(Ca) induced by ET-1 (10(-8) M) was suppressed by BQ-788. In the presence of ISO (10(-6) M), ET-1 elicited a more pronounced inhibitory effect: at 10(-9)-10(-7) M ET-1 inhibited the ISO-induced increase in I(Ca) in a concentration-dependent manner (anti-adrenergic effect). The maximum inhibition induced by ET-1 at 10(-7) M was approximately 80% of the ISO-induced response, and the IC50 value for anti-adrenergic effect of ET-1 was 4.2x10(-9) M. The anti-adrenergic effect of ET-1 (10(-8) M) was antagonized by the ET(A) antagonist FR139317 (10(-9)-10(-6) M) in a concentration-dependent manner and was partially inhibited by the ET(B) antagonist BQ-788 (10(-6) M). The anti-adrenergic effect of ET-1 was markedly attenuated by pretreatment of ventricular myocytes with pertussis toxin. The increases in I(Ca) induced by forskolin (10(-6) M), 3-isobutyl-1-methylxanthine (10(-4) M), and 8-bromo-cyclic AMP (3x10(-4) M) were also suppressed by ET-1 (10(-8) M). In summary, ET-1 has a differential effect on I(Ca) in the absence and in the presence of ISO: ET- I has a feeble biphasic action on the baseline I(Ca) and, in addition, it elicits a pronounced anti-adrenergic effect on the ISO-induced increase in I(Ca). Pertussis toxin-sensitive G protein is responsible for the anti-adrenergic effect of ET-1 on I(Ca), but the anti-adrenergic effect of ET-1 may involve also the regulation at the level of signaling process beyond the cyclic AMP generation. Anti-adrenergic effect of ET-1 on I(Ca) is mainly due to activation of ET(A) receptors but ET(B) receptors are also involved partially in the anti-adrenergic effect of ET-1 on I(Ca) in rabbit ventricular myocytes.
Watanabe
T
T
Department of Pharmacology, Yamagata University School of Medicine, Japan.
Endoh
M
M
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011817:Rabbits; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D001381:Azepines; D020746:Calcium Channels, L-Type; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D007211:Indoles; D010726:Phosphodiesterase Inhibitors; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D010566:Virulence Factors, Bordetella; C079574:FR 139317; D015124:8-Bromo Cyclic Adenosine Monophosphate; D037342:Pertussis Toxin; D011493:Protein Kinase C; D007545:Isoproterenol; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine