EVIDENCE FOR P-2-PURINOCEPTOR-MEDIATED UPTAKE OF CA2-MOSSAMBICUS) INTESTINAL BRUSH-BORDER MEMBRANE( ACROSS A FISH (OREOCHROMIS)

We have studied the effect of ATP on Ca2+ uptake in intestinal brush b order membrane vesicles (BBMVs) of the teleost tilapia (Oreochromis mo ssambicus). ATP stimulated Ca2+ uptake 12-fold over the control, with a linear time course. Ionomycin and detergent treatment did not reduce BBMVs' Ca2+ content, indicating the binding of Ca2+ to a membrane com ponent. A rank order of ATP > ADP > AMP was established for the stimul ation of Ca2+ uptake. Adenosine, vanadate, adenosine 5'-[alpha,beta-me thylene]triphosphate (a P-2x purinoceptor agonist) and adenosine 5'-[g amma-thio]triphosphate (a P-type ATPase inhibitor) were without effect , 2-Methylthioadenosine 5'-triphosphate, a P-2Y purinoceptor agonist, mimicked the stimulation by ATP. As judged from a kinetic comparison, ATP hydrolysis and the stimulation by ATP of Ca2+ uptake were not comp atible, The P-2 purinoceptor antagonist suramin and the P-2Y purinocep tor antagonist Reactive Blue-2 inhibited the Ca2+ uptake stimulated by 1 mM ATP (IC50 0.17 mM and 58 mu M respectively). We conclude that AT P-stimulated Ca2+ uptake in tilapia intestine is dissociated from ATPa se activity and is mediated through a P-2 purinoceptor.