Fig. 9. Differences in the characteristics of SCTs stimulated by ET-1, digoxin and isoproterenol. (A,B) Parts of photometry recordings from cells stimulated with either (Ai) 100 nM ET-1 or (Bi) 100 nM isoproterenol. (Aii, Bii) Traces on an expanded time scale. Arrows indicate instances when the cells were field-stimulated. The dashed grey lines illustrate the rate of increase of the field-stimulation-evoked Ca²⁺ signals and the subsequent SCTs. It is evident that for the ET-1-stimulated cell (Aii) the rate of increase of the SCT was comparable to the field-stimulation-evoked event (i.e. it was due to an action potential). By contrast, in the isoproterenol-stimulated cell, the SCT developed at a much slower rate (i.e. it was due to a Ca²⁺ wave). (C) Peak rate of Ca²⁺ signal increase during SCTs recorded from six cells incubated with ET-1, and six cells treated with isoproterenol. indicates the typical rate of increase of field-stimulation-evoked Ca²⁺ transients (E_m). , SCTs that arose with a similar rate to those triggered by field stimulation. , SCTs that were consistent with the development of Ca²⁺ waves. Italicised numbers indicate the number of SCTs measured for each data point, they also illustrate the relative proportions of events observed in each of the individual cells. (D) Proportion of SCTs that occurred as an action potential (i.e. that had a rate of increase >2000 nM s^-1) for ET-1, digoxin or isoproterenol.