Increased frequency of calcium waves in Xenopus laevis oocytes that express a calcium-ATPase

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.