Modulation of HIF-1α mRNA expression by A23187 and BAPTA-am. HepG2 cells were stimulated with A23187 (5 μM) or BAPTA-am (5 μM) under normoxia (16% O₂) or hypoxia (8% O₂) for 4 hours. HIF-1α mRNA was detected by Northern blot analysis. (A) The expression of HIF-1α mRNA under hypoxia was set to 100%. Values are means ± SEM of 3 independent culture experiments. Statistics, Student t test for paired values: ^*P ≤ .05, 16% O₂ versus 8% O₂;^**P ≤ .05, +A23187 versus control at the same pO₂. (B) Representative Northern blot analysis. Total RNA (20 μg) of each sample was subjected to Northern blot analysis with HIF-1α or β-actin antisense RNA probes. Autoradiographic signals were obtained by chemiluminescence and scanned by videodensitometry.