Cytosolic Ca2+ during atrial natriuretic peptide secretion from cultured neonatal cardiomyocytes.
Mechanisms of atrial natriuretic peptide (ANP) release were studied in neonatal rat heart atrial and ventricular myocytes cultured on Cytodex 3 microcarriers. For simultaneous observations of cytosolic free calcium concentration ([Ca2+]f) and ANP secretion, the culture was packed in a chromatography column, inserted into the cell holder of a spectrofluorometer was perifused with a buffer solution. [Ca2+]f was measured by the fluorescent calcium indicator Fura-2 and ANP in the effluent perfusate by radioimmunoassay. No cell damage was observed and the basal ANP secretion rate and [Ca2+]f were comparable with values obtained by other methods. K(+)-induced depolarization raised [Ca2+]f by 50%, but it rapidly declined again to a steady level 10-20% above the baseline. The calcium channel agonist Bay k8644 elicited a similar temporal pattern of [Ca2+]f changes and 1 microM ionomycin induced a 100-fold increase in [Ca2+]f with a slow re-establishment of the original baseline. None of these stimuli increased the ANP secretion rate of the atrial or ventricular myocytes. Protein kinase C activation by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulated ANP secretion from the atrial myocytes, while the ventricular myocytes were unresponsive to TPA. It is concluded that Ca2+ is not the main mediator in the regulation of ANP release in cultured neonatal heart cells.
Uusimaa
P A
PA
Department of Medical Biochemistry, University of Oulu, Finland.
Ruskoaho
H
H
Leppäluoto
J
J
Hassinen
I E
IE
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D016275:Atrial Function; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D002118:Calcium / Q000032:analysis*; D002478:Cells, Cultured; D003600:Cytosol / Q000737:chemistry; D004789:Enzyme Activation / Q000187:drug effects; D006321:Heart / Q000502:physiology*; D009206:Myocardium / Q000166:cytology; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D012636:Secretory Rate / Q000187:drug effects; D013268:Stimulation, Chemical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016276:Ventricular Function
D009320:Atrial Natriuretic Factor; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium