Figure 3.

Spontaneous contractions induced by 20 nM hU-II in a right atrial trabeculum obtained from a 58-year-old male patient undergoing coronary artery bypass surgery. Tissues were paced using forward and backward staircases, as described in the Methods. No spontaneous contractions were observed during this procedure (not shown). The tissue was then paced at 1 Hz and 20 nM hU-II was added to the bath (arrow head). Upon equilibration, the tissue was stimulated at 2, 1, 0.5, 0.2 and 0.1 Hz, with a 2 min quiescent period after each change of frequency (upper horizontal lines). Note the spontaneous contractions that occurred during quiescent periods.