QPCR was used to measure relative levels (percentage of total) of mRNA encoding isoforms of AC and IP₃R in HEK-PR1 cells. Results are means ± SEM from three experiments, each performed in duplicate. The absence of AC2, AC4, and AC8 is consistent with a previous semiquantitative RT-PCR analysis, although a low level of AC5 was detected (Ludwig and Seuwen, 2002). The preponderance of IP₃R2 and IP₃R3 in HEK cells is consistent with results from immunoblotting (Wojcikiewicz, 1995).