Inositol trisphosphate receptor activation is required for generation of calcium waves and the amplification of action potential-evoked calcium rises. a, Muscarine-evoked calcium waves were reversibly blocked by 10 mm caffeine. Rises in calcium are plotted as ΔF/F in arbitrary units (A.U.). Nuc, Nucleus;Dend, dendrite. b, Superimposed somatic calcium transients, plotted as ΔF/F, in response to a train of action potentials are shown in the presence of caffeine (thin trace) and after addition of muscarine (thick trace). After washout of caffeine (traces onright), reapplication of muscarine to the same cell now evokes a large regenerative calcium rise. c, When heparin (500 μg/ml) was included in the internal solution, calcium waves (top traces) and action potential-induced amplification (bottom traces) were not observed after application of muscarine. d, In heparin-loaded cells, InsP3 receptors are blocked, as shown by the lack of response to uncaging of InsP3. e, Muscarine application still blocked the AHP evoked by a train of action potentials in heparin-loaded cells, showing that heparin did not disrupt the activation of second-messenger systems.
