Ca(2+) is the most important second messenger controlling a variety of intracellular processes by oscillations of the cytosolic Ca(2+) concentration. These oscillations occur by Ca(2+) release from the endoplasmic reticulum (ER) into the cytosol through channels and the re-uptake of Ca(2+) into the ER by pumps. A common channel type present in many cell types is the inositol trisphosphate receptor (IP(3)R), which is activated by IP(3) and Ca(2+) itself leading to Ca(2+) induced Ca(2+) release (CICR). We have shown in an experimental study, that Ca(2+) oscillations are sequences of random spikes that occur by wave nucleation. We use here our recently developed model for Ca(2+) dynamics in 3 dimension to illuminate the role of IP(3)R clustering within spatial extended systems.