Functional Coupling of Human L-Type Ca2+Channels and Angiotensin AT1A Receptors Coexpressed inXenopus laevis Oocytes: Involvement of the Carboxyl-Terminal Ca2+ Sensors
Abstract
A human recombinant L-type Ca2+ channel (α1C,77) was coexpressed with the rat angiotensin AT1A receptor in Xenopus laevis oocytes. In oocytes expressing only α1C,77 channels, application of human angiotensin II (1–10 μm) did not affect the amplitude or kinetics of Ba2+ currents (IBa). In sharp contrast, in oocytes coexpressing α1C,77channels and AT1A receptors, application of 1 nm to 1 μm angiotensin gradually and reversibly inhibited IBa, without significantly changing its kinetics. The inhibitory effect of angiotensin on IBawas abolished in oocytes that had been preincubated with losartan (an AT1A receptor antagonist) or thapsigargin or injected with 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetate, pertussis toxin, guanosine-5′-O-(2-thio)diphosphate, or heparin, suggesting that the recombinant α1C channels were regulated by angiotensin through G protein-coupled AT1A receptors via activation of the inositol trisphosphate-dependent intracellular Ca2+ release pathway. Consistent with this hypothesis, no cross-signaling occurred between the AT1A receptor and a splice variant of α1Clacking Ca2+ sensors (α1C,86). The data suggest that the regulation of recombinant L-type Ca2+channels by angiotensin is mediated by inositol trisphosphate-induced intracellular Ca2+ release and occurs at the molecular motif responsible for the Ca2+-induced inactivation of the channels.
Footnotes
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Send reprint requests to: Dr. Martin Morad, Georgetown University Medical Center, Department of Pharmacology, 3900 Reservoir Road N.W., Washington, DC 20007. E-mail:moradm{at}gunet.georgetown.edu
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This work was supported in part by a grant-in-aid from the American Heart Association, Nation’s Capital Affiliate (to N.M.S.), and National Institutes of Health Grants HL16152 (to M.M.) and AG08226 and GM08386 (to D.R.A.).
- Abbreviations:
- PTX
- pertussis toxin
- IP3
- inositol trisphosphate
- BAPTA
- 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetate
- GDPβS
- guanosine-5′-O-(2-thio)diphosphate
- ICl(Ca)
- Ca2+-activated Cl−current
- IBa
- Ba2+ current
- ICl
- Cl− current
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
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- Received June 24, 1998.
- Accepted September 3, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
