Figure 7.

Effects of interfering with Ca²⁺ influx on the Ca²⁺ oscillations. A, In a preloaded MLI, a 2 μm quisqualate bath applied during the time indicated by the black bar above the trace fails to elicit any change in Ca²⁺ when extracellular Ca²⁺ is absent (as indicated by the discontinuous gray bar above the trace). A small response to the agonist develops within 2.5 min after Ca²⁺ is readmitted (as indicated by the gray solid bar above the traces). B, In a different MLI, in which the oscillatory response to quisqualate is initiated in the presence of Ca²⁺, removal of this cation does not stop the oscillations. When the agonist is removed and Ca²⁺ is readmitted, there is a 2-min-long Ca²⁺ plateau. C, Time course for the effects of extracellular Ca²⁺ removal (during the bar above the data points) on the peak ΔF/F_o rises obtained from a MLI dendrite on direct extracellular stimulation of the dendrite. The MLI is the same as used for the experiment shown in B. D, Pooled data from preloaded MLIs on the effects of Ca²⁺ removal and of block of L-type channels by 20 μm nimodipine (Nimo). Data were analyzed in terms of the peak of the ΔF/F_o signals induced by quisqualate (top) and their oscillation frequency (bottom). The notation “before Quis” refers to experiments in which Ca²⁺ removal or nimodipine treatment were started 5 min before quisqualate was applied (example in A). The notation “during Quis” refers to experiments in which Ca²⁺ removal or nimodipine treatment was performed during the oscillatory response (example in B). In the “during Quis” condition, peak ΔF/F_o values were measured 3–5 min after Ca²⁺ removal or nimodipine treatment, and the frequency of oscillations was calculated from the ensuing 2–3 min of recording. n = 4 for groups Ctl vs 0 Ca before Quis and Ctl vs Nimo before Quis, and n = 6 for the Ctl vs 0 Ca during Quis and the Ctl vs Nimo during Quis groups. * indicates groups in which p was ≤0.05 using the paired Student's t test.