Liver cytosolic non-dialysable factor(s) can counteract GTP-dependent Ca2+ release in rat liver microsomal fractions.
Readdition to rat liver microsomes of dialysed liver post-microsomal supernatant resulted in an almost complete inhibition of the Ca2+-releasing effect of GTP. Such inhibition was heat-labile, and was associated with non-ultrafiltrable supernatant components with a molecular weight higher than 30,000 D. A preliminary fractionation of liver supernatant showed that the inhibitory effect is recovered in the 40-50% ammonium sulfate-precipitated proteins, with an approx. 10-fold enrichment. The active ammonium sulfate fraction did not modify the GTP-induced Ca2+ increase of passive Ca2+ efflux from microsomes, nor did it affect microsomal GTP hydrolysis, which is likely required for its Ca2+ releasing effect. The active ammonium sulfate fraction appears to markedly favour the translocation of GTP-released Ca2+ into a microsomal GTP-insensitive pool. Separation of liver microsomes in smooth and rough fractions revealed that such GTP-insensitive Ca2+ pool is almost completely associated with smooth microsomes.
Istituto di Patologia Generale dell'Università di Siena, Italy.
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Fulceri
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Romani
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G
Bellomo
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Benedetti
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D006160:Guanosine Triphosphate; D002118:Calcium