Figure 3.

Duty cycle continuously regulates LP I_A density, and tonic 5 nm DA gates this regulation. A, Experimental protocol for examining the activity dependence of LP I_A. Left, Diagram represents LP slow-wave activity at t = −10 min. Plateau duration (250 ms), peak (−40 mV), and nadir (−60 mV) voltages, and cycle period (850 ms) were measured and used to create three voltage protocols: −100%, 0%, and 50% ΔDC. Voltage protocols were always specifically designed for each cell based on measurements from that cell. The protocols were used in the experiments diagramed on the right. At t = −5 min, TTX was bath-applied and the 0% ΔDC protocol was initiated. At t₀, the current was measured (red asterisk) and one of the two series of voltage protocols shown was implemented in the presence or absence of 5 nm DA. Each voltage protocol lasted 20 min, and the current was measured at the end of each protocol as indicated by red asterisks. The order of the voltage protocols was varied between experiments as shown in the two timelines. B, LP I_A traces from a single exemplar experiment show that LP I_A is continuously regulated by duty cycle. Difference current traces are shown for the indicated time points. Calibration: 100 nA, 100 ms. The 20 min alterations in duty cycle produced bidirectional alterations in peak I_A. C, Increasing LP duty cycle reduces I_A, decreasing LP duty cycle enhances I_A, and 5 nm DA blocks LP I_A activity dependence. The experiment diagrammed in Figure 3A was performed in the presence or absence of 5 nm DA. Plot represents the mean percent change in peak I_A produced by a given change in duty cycle [(t₆₀/t₄₀ or t₂₀/t₀) − 1 × 100]. Green asterisks indicate significant difference within a treatment group using paired t tests (t₀ vs t₂₀, or t₄₀ vs t₆₀; p ≤ 0.05). Black asterisks indicate significant differences using a one-way ANOVA with Bonferroni's multiple comparisons post hoc tests to compare selected pairs, as indicated (F_(3,31) = 8.512; p = 0.0003).