Fig. 5.
Trains of 5 msec pulses always evokeCm responses with equal or greater Ca2+ efficacy than trains of 40 msec pulses in individual cells. A–D, Examples of capacitance responses to 5 and 40 msec pulse trains from four separate cells. In all panels, cumulative Cm increases are plotted against cumulative Ca2+ entry with the 5 msec (open triangles) and 40 msec duration pulse train (closed squares) superimposed. Cells were selected to illustrate pairs of responses that were (A) both depressed, (B) standard curve versus depressed, (C) enhanced efficacy versus depressed, (D) enhanced versus standard curve. Cells (A) Chr172, (B) N112704, (C) Chr061, (D) N122202.E, Percentage of cells stimulated with both 5 and 40 msec pulse trains that exhibit particular pairs of Ca2+ efficacy. The Ca2+-exocytosis relationship for each 5 and 40 msec pulse train was classified as either depressed (D), enhanced (E), or one that obeys the standard transfer function (S) and expressed as a percentage of total cells stimulated with the two-pulse protocols (n = 73). In the majority of cells, 5 msec pulse trains evoked exocytosis with greater Ca2+ efficacy than 40 msec pulse trains (S-D, E-D, E-S), whereas in the remaining 18% the trains evoked responses with similar efficacies (D-D, E-E).