Figure 2

Norepinephrine increases SAN discharge by increasing ThV _os and V _os . The SAN was spontaneously active in 13 mM [K⁺]_o. In panel a, the shaded areas emphasize V_os and ThV_os, as labeled. The dash lines extrapolate the depolarizing slope of ThV_os. NE was administered between the vertical arrows (b-g panels). Inset 1 shows the gradual increase of ThV_os (dots) and V_os (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.