Abstract
The ability of angiotensin II (AII) to regulate [Ca++]i in human neuroblastoma (SH-SY5Y) cells stably expressing recombinant rat AT1A receptors was investigated using microfluorimetric methods, and compared to responses obtained by stimulation of native muscarinic receptors. Applications of AII or carbachol produced biphasic rises of [Ca++]i, but in Ca++-free solutions (containing 1 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N,’N’-tetraacetic acid), both agonists produced only transient monophasic rises of [Ca++]i, and second applications were without effect. Application of Ca++ o (2.5 mM) to cells after exposure to either agonist produced a Ni2+-sensitive rise of [Ca++]i in the absence of agonist (“capacitative Ca++ influx”). After removal of Ca++ o, both AII and carbachol elicited a second rise of [Ca++]i. Thapsigargin (1 μM) prevented these second rises of [Ca++]i. During capacitative Ca++ influx, application of AII failed to produce a further rise of [Ca++]i. In contrast, carbachol produced a further rise of [Ca++]i, attributable to activation of both nicotinic and muscarinic receptors, because it was reduced (but not abolished) by mecamylamine (1 μM) and was observed when muscarine was used as the agonist. Thus, activation of recombinant AT1Aand muscarinic receptors in SH-SY5Y cells leads to mobilization of Ca++ from a common intracellular pool, and stimulates capacitative Ca++ influx. Muscarinic (but not AII) receptor occupancy is capable of stimulating an additional Ca++influx pathway.
Footnotes
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Send reprint requests to: Dr. Chris Peers, Institute for Cardiovascular Research, Leeds University, Leeds LS2 9JT, U.K.
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↵1 This study were supported by the British Heart Foundation and the Leeds University Research Fund.
- Abbreviations:
- AII
- angiotensin II
- EGTA
- ethylene glycol-bis(β-aminoethyl ether)N,N,N’,N’-tetraacetic acid
- PBS
- phosphate-buffered saline
- HEPES
- (N-[2-hydroxyethyl]piperazine-N’-[2-ethanesulfonic acid]
- AM
- acetoxy methylester
- NA
- noradrenaline
- DMPP
- dimethylphenylpiperazinium
- [Ca++]i
- intracellular calcium concentration
- IP
- inositol phosphate
- Received August 27, 1996.
- Accepted February 24, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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