Effect of apelin-13 on activity of large conductance Ca²⁺-activated K⁺ (BK_Ca ) channels of rat middle cerebral arterial VSM cells.

<p>Whole-cell K⁺ currents were recorded at room temperature in response to successive voltage pulses of 800 ms duration, increasing in 10-mV increments from -70 mV to +50 mV before and after the treatment of apelin-13 (0.001-1 µM). <b>A</b>-<b>D</b>: representative tracings depicting the currents recorded from a single VSM cell before and after treatment with apelin-13 (0.1 µM, 5 min) or iberiotoxin (IBT) (100 nM, 5 min). <b>E</b>: I-V curve plots of BK_Ca currents at baseline and after application of apelin-13 (0.1 µM, 5 min). <b>F</b>: Bar graph summarizing the concentration-dependent effect of apelin-13 (0.001-1 µM) on average current density (pA/pF) at +50 mV. Values are mean±SEM (n=6 to 14 cells). *<i>P</i><0.05 indicates a significant difference from the corresponding control value. <b>G</b>: A representative VSM cell isolated from rat middle cerebral arteries under optical phase and fluorescence imaging. Fluorescence micrographs demonstrate the APJ receptor expression in VSM cells immunostained with anti-alpha smooth muscle actin antibodies (red) and anti-APJ receptor antibodies (green). The overlap of these two images shows that green fluorescence is VSM cell-located.