Rat platelets are deficient in internal Ca2+ release and require influx of extracellular Ca2+ for activation.
Calcium fluxes were studied in fura-2-labeled rat platelets. Thrombin, ADP and ionomycin induced rapid mobilization of internally stored Ca2+, which resulted in only a moderate increase of cytosolic [Ca2+]i. Thrombin and ADP stimulated influx of extracellular Ca2+, which was monitored as uptake of 45Ca2+ and of Mn2+. With either agonist, the influx of Ca2+ magnified the initial increase of [Ca2+]i. Since responses of rat platelets were dependent on external [Ca2+], we conclude that Ca2+ influx complements the mobilization of internal stores to reach sufficiently high [Ca2+]i for full activation. A regulatory effect of protein kinase C modulators was observed on both agonist-induced elevation of [Ca2+]i and receptor-mediated Ca2+ entry.
Heemskerk
J W
JW
Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
Feijge
M A
MA
Rietman
E
E
Hornstra
G
G
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000097:blood* / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D015759:Ionomycin / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013917:Thrombin / Q000494:pharmacology
D005456:Fluorescent Dyes; D008345:Manganese; D004533:Egtazic Acid; D015759:Ionomycin; D000244:Adenosine Diphosphate; D009532:Nickel; D011493:Protein Kinase C; D013917:Thrombin; D002118:Calcium; D016257:Fura-2