Fig. 3.

Agonists of receptors in the D1 family increase the duration of the regenerative depolarization.A, Superimposed records of plateau potentials in the presence of TTX (1 μm) and with Ba²⁺replacing Ca²⁺. Washing off of SKF 82958 partially restored the surface of the plateau. The inset shows a plateau potential recorded in normal Ringer's solution, in addition to that recorded during bath perfusion of TTX, with Ba²⁺ instead of Ca²⁺.B, Time course of the action of D1-like agonists (SKF 81297 and 82958; 3–5 μm). The bar shows the addition of agonists to bath perfusion. *Significantly different from pretest values. C, The D1 receptor antagonist, SCH 23390, reversed the action of SKF 81297, whereas the selective D2 receptor antagonist, raclopride, had no effect, as illustrated by representative traces of plateau potentials. Box plotsof the changes in the plateau potential surface induced by D1-like agonists (3–5 μm) together with SCH 23390 (10 μm) or raclopride (5 μm) substantiate this finding.