When inositol 1,4,5-trisphosphate (IP3) receptors are activated, calcium is released from intracellular stores in excitatory propagating waves that annihilate each other upon collision. The annihilation phenomenon suggests the presence of an underlying refractory period that controls excitability. Enhanced calcium-adenosine triphosphatase (ATPase) activity might alter the refractory period of calcium release. Expression of messenger RNA encoding the avian calcium-ATPase (SERCA1) in Xenopus laevis oocytes increased the frequency of IP3-induced calcium waves and narrowed the width of individual calcium waves. The effect of SERCA1 expression on calcium wave frequency was dependent on the concentration of IP3 and was larger at higher (1 μM) than at lower (0.1 μM) concentrations of IP3. The results demonstrate that calcium pump activity can control IP3-mediated calcium signaling.
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