A comparative study of histamine and K+ effects on (Ca(2+)-Mg2+)-ATPase activity in synaptosomes.
Histamine (10(-4) M) and 60 mM K+, but not 60 mM Na+ or 60 mM choline+, increased the maximal synaptosomal (Ca(2+)-Mg2+)-ATPase activity by 15 and 36% respectively and decreased the extrasynaptosomal Ca2+ concentration necessary to reach it. Histamine and K+ enhanced the synaptosomal (Ca(2+)-Mg2+)-ATPase activity in a concentration-dependent manner. In synaptic plasma membranes histamine (10(-4) M) and 60 mM choline+ were not able to alter the enzymatic activity, however 60 mM K+ and 60 mM Na+ elevated (Ca(2+)-Mg2+)-ATPase activity by 20 and 15%, respectively, without altering the affinity for Ca2+. Histamine effects in synaptosomes were mediated by H2 receptor stimulation. 3-Isobutyl-1-methyl-xanthine (10(-4) M) potentiated (15%) the maximal histamine effect. The slow Ca2+ channel antagonists verapamil and diltiazem, both at 10(-6) M, completely inhibited K+ effects in synaptosomes, however histamine effects were only blocked by verapamil. The data suggest that K+ and histamine effects on synaptosomal (Ca(2+)-Mg2+)-ATPase activity are mediated by increases of intrasynaptosomal Ca2+ levels. Moreover, histamine effects on synaptosomal enzyme activity were mediated by cAMP.
Rodriguez
R
R
Dpto bioquímica y Biología Molecular, Facultad de Medicina, Universidad Autónoma de Barcelona, Spain.
Toledo
A
A
Sabriá
J
J
Rodriguez
J
J
Blanco
I
I
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002794:Choline / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006632:Histamine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D011738:Pyrilamine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology*; D014700:Verapamil / Q000494:pharmacology
D006632:Histamine; D011899:Ranitidine; D012964:Sodium; D014700:Verapamil; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D004110:Diltiazem; D011738:Pyrilamine; D002122:Calcium Chloride; D002794:Choline; D011188:Potassium; D015056:1-Methyl-3-isobutylxanthine