Dissociation between phytohaemagglutinin-stimulated generation of inositol phosphates and Ca2+ increase in human mononuclear leucocytes.
We have tested whether phytohaemagglutinin (PHA)-stimulated generation of inositol phosphates (IP) and increases in intracellular Ca2+ can be dissociated in human mononuclear leucocytes. Lowering the incubation temperature from 37 degrees to 25 degrees C decreased PHA-stimulated IP generation by more than 80%, but only marginally affected PHA-stimulated Ca2+ increases. In the absence of extracellular Ca2+, PHA did not stimulate IP generation or Ca2+ increases, although PHA binding to its acceptor sites was not impaired. Increasing extracellular Ca2+ up to 0.15 mM enhanced PHA-stimulated PHA generation but this increase was attenuated by further increasing extracellular Ca2+ to 2.6 mM. Increasing extracellular Ca2+ to 0.3 mM also enhanced PHA-stimulated Ca2+ increases, and further increasing extracellular Ca2+ did not affect it. Co-treatment with 100 microM-prostaglandin E2 completely abolished PHA-stimulated IP generation, but inhibited Ca2+ increases by only 20-30%. These results could be explained by IP-generation-independent Ca2+ increases or by non-linear coupling of IP generation to Ca2+ increases. Since the PHA concentrations required to increase Ca2+ were greater than those required for IP generation, the latter hypothesis can be excluded. Furthermore, the Ca2+ ionophore ionomycin increased intracellular Ca2+ and weakly stimulated IP generation, but with very similar concentration-response relationships. Our data suggest that PHA-stimulated IP generation and Ca2+ increases in human mononuclear leucocytes mainly occur independently of one another rather than sequentially.
Michel
M C
MC
Department of Medicine, University of Essen Medical School, Federal Republic of Germany.
van Tits
L J
LJ
Trenn
G
G
Sykora
J
J
Brodde
O E
OE
D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D015232:Dinoprostone / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis*; D015759:Ionomycin / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010835:Phytohemagglutinins; D013050:Spectrometry, Fluorescence; D013696:Temperature
D002413:Cations, Divalent; D007295:Inositol Phosphates; D010835:Phytohemagglutinins; D015759:Ionomycin; D015232:Dinoprostone; D002118:Calcium