Vascular Angiotensin II Receptor and Calcium Signaling in Toadfish

• Published in: General and comparative endocrinology 1999-07, Vol.115 (1), p.122-131
• Main Authors: Qin, Ze-lian, Yan, Hong-Q., Nishimura, Hiroko
• Format: Article
• Language: English
• Subjects: 1-Sarcosine-8-Isoleucine Angiotensin II - pharmacology; 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester - pharmacology; angiotensin antagonist; angiotensin binding; Angiotensin II - metabolism; Angiotensin II - pharmacology; Angiotensin Receptor Antagonists; angiotensin receptor subtypes; Animals; Blood Pressure - drug effects; Blood Vessels - metabolism; Calcium - metabolism; Calcium Signaling; Cell Membrane - metabolism; Female; Fishes - physiology; Imidazoles - pharmacology; losartan; Losartan - pharmacology; Male; Marine; Opsanus tau; Potassium - pharmacology; Pyridines - pharmacology; Receptors, Angiotensin - physiology; toadfish; vascular angiotensin receptor
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1006/gcen.1999.7297

The renin–angiotensin system evolved during the early evolution of vertebrates and regulates blood pressure/blood volume homeostasis in nonmammalian and mammalian vertebrates. Properties of vascular angiotensin (ANG) receptors and signal pathways in primitive animals are, however, not well understood. We aimed to determine whether vascular ANG II receptors in the toadfish, Opsanus tau, an aglomerular teleost, pharmacologically resemble either the ANG subtype 1 receptor (AT1) or the subtype 2 receptor (AT2) by examining (i) the effects of selective ANG receptor antagonists on ANG II-induced vasopressor action and binding and (ii) ANG II's effect on cytosolic Ca2+ signaling. [Asn1, Val5]ANG II (native teleost ANG II) dose-dependently increased the mean arterial pressure of conscious toadfish. ANG II-induced pressor responses (100–500 ng/kg) were inhibited substantially (79–83%) by [Sar1, Ile8]ANG II (5 μg· kg−1+ 5 μg·kg−1· min−1) and moderately (34–53%) by losartan (AT1 antagonist, 10 mg/kg+20 mg·kg−1·h−1) and by PD 123319 (AT2 antagonist, 10 mg/kg+20 mg· kg−1· h−1) (36–60%). Likewise, the [Asp1, Val5, His9]ANG I-induced pressor effect was completely eliminated by an ANG I-converting enzyme inhibitor, SQ 14,225. Specific 125I-ANG II binding to vascular smooth muscle (VSM) membrane fractions was displaced completely by [Asn1, Val5]ANG II and [Sar1, Ile8]ANG II. Losartan, but not PD 123319, partly displaced ANG II binding at 10−10–10−6 M. Furthermore, ANG II (10−7 or 10−8 M) caused a rapid, transient increase in the cytosolic Ca2+ signal (fluorescence ratio (FR) of 340/380 nm) of isolated VSM tissues measured by fura-2 and a dual wavelength fluorospectrometer, whereas extracellular K+ induced sustained, dose-dependent (P