Angiotensin II receptor-mediated stimulation of cytosolic-free calcium and inositol phosphates in chick myocytes.
We have described previously positive inotropy and increased levels of inositol-l-phosphate as in vitro responses to angiotensin II in cardiac tissue. In this study, changes in cardiac myocyte-free cytosolic calcium stimulated by angiotensin II were monitored with the fluorescent calcium indicator dye Fura-2. There was an initial peak transient increase followed by a sustained increase in cytosolic-free calcium in response to angiotensin II (10(-9)-10(-6) M). The peak transient response in cytosolic-free calcium after addition of angiotensin II (10(-7) M) occurred at 23 +/- 4 sec and was stimulated 2.16-fold (332 +/- 56 nM) above basal levels (154 +/- 14.7 nM). The calcium response was blocked or reversed by addition of verapamil (10(-8) M), lanthanum (0.2 mM) and zero calcium buffer. Angiotensin II receptor-mediated stimulation of inositol phosphates was quantified after separation by high-performance liquid chromatography in cultured chick heart cells prelabeled with L-myo-[1,2-3H(N)]inositol. A time course indicated that the peak response of the angiotensin II (10(-8) M)-stimulated increase in inositol-1,4,5-trisphosphate was at 30 sec. Angiotensin II (10(-8) M) significantly stimulated inositol-1,4-diphosphate (45%) and inositol-1,4,5-trisphosphate (78%) above basal levels. Bordetella pertussis toxin treatment of myocyte cultures in doses (500 ng/ml, 24 hr) shown to fully ADP-ribosylate a toxin-sensitive 41 KD alpha-subunit, blocked completely the angiotensin II-stimulated increases in inositol 1,4-diphosphate, inositol-1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate. The rise in cytosolic-free calcium in response to angiotensin II was not blocked or inhibited by toxin pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Baker
K M
KM
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania.
Singer
H A
HA
Aceto
J F
JF
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000032:analysis*; D002478:Cells, Cultured; D002642:Chick Embryo; D003600:Cytosol / Q000032:analysis*; D019204:GTP-Binding Proteins / Q000502:physiology; D007295:Inositol Phosphates / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000502:physiology; D011945:Receptors, Angiotensin / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D011945:Receptors, Angiotensin; D010566:Virulence Factors, Bordetella; D000804:Angiotensin II; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D002118:Calcium