Fig. 9. ET increases fractional Ca²⁺ release from SR and perinuclear stores. (A) Original recording of cytoplasmic (black) and nuclear (red) CaTs before (left) and after (right) ET application. Each time, two electrically stimulated CaTs and a caffeine-induced CaT are shown. The ET effect on electrically stimulated CaTs shown here was the largest effect recorded in this series of experiments. Still there was no increase in Ca²⁺ load of either SR or perinuclear (PN) stores, indicating that ET augmented the CaT by increased fractional release rather than elevation of Ca²⁺ store content. (B) Average values of Ca²⁺ store content (left, normalised to control) and fractional Ca²⁺ release (FCR) from SR and PN stores (middle) before and following application of ET (n=7) or ISO (n=7). Right, ET- and ISO-induced increases in fractional release from SR and PN stores (FCR). Means ± s.e.m. of seven atrial myocytes for each case.