Opposing effects of alpha 1-adrenergic receptor subtypes on Ca2+ and pH homeostasis in rat cardiac myocytes.
We examined the effect of alpha 1-adrenergic receptor (AR) subtypes on contraction, cytosolic Ca2+ concentration ([Ca2+]i), and cytosolic pH (pHi) of rat ventricular myocytes loaded with the Ca2+ indicator indo 1 or the pH indicator carboxyseminaphthorhodafluor-1. Nonselective alpha 1-AR stimulation was effected with phenylephrine plus nadolol. alpha 1-AR subtype stimulation was achieved with alpha 1-AR and chloroethylclonidine (CEC) or with alpha 1-AR and WB-4101. Cells were in bicarbonate buffer with 0.5 mM Ca2+ and were electrically stimulated at 0.5 Hz. Results show that 1) nonselective alpha 1-AR stimulation increased twitch and [Ca2+]i transient amplitudes, myofilament response to Ca2+, and pHi; 2) alpha 1-AR plus CEC increased twitch and [Ca2+]i transient amplitudes and also enhanced myofilament response to Ca2+ via cytosolic alkalinization; 3) alpha 1-AR plus WB-4101 decreased twitch and [Ca2+]i transient amplitudes and also pHi; and 4) cytosolic acidification due to alpha 1-AR plus WB-4101 was abolished by protein kinase C inhibition (staurosporine pretreatment) or downregulation (prolonged exposure to phorbol esters). In summary, the net effects of alpha 1-adrenergic stimulation on contraction, [Ca2+]i, and pHi are due to opposing WB-4101- and CEC-sensitive alpha 1-AR subtype signaling pathways.
Gambassi
G
G
Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA.
Spurgeon
H A
HA
Ziman
B D
BD
Lakatta
E G
EG
Capogrossi
M C
MC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D004338:Drug Combinations; D004357:Drug Synergism; D005456:Fluorescent Dyes; D006706:Homeostasis / Q000502:physiology*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007211:Indoles; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004338:Drug Combinations; D005456:Fluorescent Dyes; D007211:Indoles; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; C051731:chlorethylclonidine; D006859:Hydrogen; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D003000:Clonidine; C048960:indo-1; D002118:Calcium