Fig. 1. Generation of frequency-manipulated [Ca²⁺]_i oscillations during agonist stimulation. [Ca²⁺]_i oscillations are generated by alternately exposing intracellular-Ca²⁺-store-depleted EC monolayers to Ca²⁺-free/EGTA or Ca²⁺-containing (1.5 mM) HBS (see Materials and Methods) in the absence of (left-hand column) and presence of (right-hand column) 1 µM histamine. Average [Ca²⁺]_i was determined from 30-40 ECs with the same amplitude of oscillation of 0.9 µM and spike duration of 30 seconds but the varied oscillation frequencies of 0.1, 0.3, 0.5 or 0.7 oscillations/minute (A-D, respectively).