Phospholipase C modulates automaticity of canine cardiac Purkinje fibers.
Alpha-1 adrenergic agonists increase cardiac Purkinje fiber automaticity and elevate D-myo-inositol-trisphosphate (IP3) levels. To learn about the relationship between phosphoinositide metabolism and the modulation of cardiac rhythm, we used phospholipase C to activate phosphoinositide hydrolysis in an alpha-1 receptor-independent fashion and determined whether this intervention modulated automaticity. We used standard microelectrode techniques to study automaticity in adult Purkinje fiber bundles, fluorescence microscopy to study fura-2 fluorescence in isolated Purkinje and ventricular myocytes and standard biochemical techniques to measure inositol phosphate production in ventricular myocytes. Phospholipase C increased Purkinje fiber automaticity, a process that was enhanced by 10 mM lithium (which had no effect alone) and suppressed by verapamil or ryanodine (both 10 microM). Superfusion with 12-O-tetradecanoyl-phorbol-13-acetate phorbol ester, phospholipase D and A2, as well as L-alpha-phosphatidic acid, trypsin and D-myo-inositol-1-phosphate, D-myo-inositol-1,4-bisphosphate, IP3 and D-myo-inositol-1,4,5,6-tetrakisphosphate did not affect automatic rate or transmembrane potentials. Biochemical studies of ventricular myocytes demonstrated a phospholipase C-induced increase in intracellular and extracellular IP3, D-myo-inositol-1,4-bisphosphate and D-myo-inositol-1-phosphate at 3 min, with the extracellular increase persisting thereafter. Fluorescence microscopy with fura-2 revealed that phospholipase C increased systolic-free calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
Viamonte
V M
VM
Department of Pharmacology, Columbia University College of Physicians & Surgeons, New York, New York.
Steinberg
S F
SF
Chow
Y K
YK
Legato
M J
MJ
Robinson
R B
RB
Rosen
M R
MR
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004285:Dogs; D006329:Heart Conduction System / Q000187:drug effects*; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D010716:Phosphatidylinositols / Q000378:metabolism; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000494:pharmacology*
D010716:Phosphatidylinositols; D008094:Lithium; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium