Fig. 2. Agonist stimulation increases the efficiency of VCAM1 gene expression that is regulated by [Ca²⁺]_i oscillation frequency. EC monolayers were exposed to conditions that generated [Ca²⁺]_i oscillations with the same amplitude of 0.9 µM and four different oscillation frequencies of 0.1, 0.3, 0.5 and 0.7 oscillations/minute, in the presence or absence of 1 µM histamine stimulation. Then, total RNA was isolated for subsequent real-time RT-PCR for determination of VCAM1 mRNA expression. Agonist stimulation shifts the frequency–gene-expression curve to the left and decreases the optimal [Ca²⁺]_i oscillation frequency from 0.45 oscillations/minute in the absence of histamine to 0.3 oscillations/minute in the presence of histamine stimulation (non-linear Lorentzian regression analysis, P<0.05, n=3 for each).