Norepinephrine increases SAN discharge by increasing ThV
. The SAN was spontaneously active in 13 mM [K+]o. In panel a, the shaded areas emphasize Vos and ThVos, as labeled. The dash lines extrapolate the depolarizing slope of ThVos. NE was administered between the vertical arrows (b-g panels). Inset 1 shows the gradual increase of ThVos (dots) and Vos (see rectangle) by NE. In inset 2, means and SEM in control and in the presence of NE are shown. Other explanations are as in the legend of Fig.1.