Effect of Alternating Electric Current on Pulsation Mode of Rat Major Arteries In Situ

In experiments on narcotized rats, the electrical potential and impedance of isolated segment of the right femoral and/or carotid artery were simultaneously recorded in situ via two extracellular nonpolarizable Ag/AgCl electrodes mounted along the arteries at the interelectrode distance of 4 mm. The active, passive, and intermediate pulsing modes of arterial segment were determined according to the phase relations between its electrical impedance and BP, which was simultaneously measured in the symmetrical part of the respective left artery and used to assess pressure in the examined segment. The study assessed the effect of amplitude (0.2-2.0 mA) of alternating probe current (100 kHz), which was used to measure the electrical impedance of arterial segment, on its pulsing mode. The pulsing mode determined at the initial minimal probe current of 0.2 mA was passive with out-of-phase pulsatile oscillations of electrical impedance and BP. After elevation of the probe current amplitude to maximal level of 2 mA, these oscillations became in-phase indicating transition of the arterial segment to active pulsing mode. This transition was accompanied by appearance of arterial voltage impulses synchronized with BP upstrokes and an 11-fold median increase in the peak-to-peak value of electrical impedance oscillations with the interdecile range of 7-15 (N=28). Under moderate amplitude of probe current (0.3-0.5 mA), the intermediate mode of arterial pulsing was observed featured by a delayed, weak, and short active constriction during BP front, which was insufficient to resist and counterbalance the dilating effect of rising BP. In this case, the pulsatile oscillations of electrical impedance were smaller than those observed in active or passive pulsing modes indicating a possibility to stabilize the arterial diameter during pulsatile oscillations of BP. The effect of alternating electric current on the mode of arterial pulsation is explained with electrical model of smooth muscle cell membrane reflecting the rectifying features of potassium channels and predicting membrane hyperpolarization in response to external alternating current passing across the cell. The visibilities of therapeutic neurotropic and angiotropic stimulation with alternating electric current are discussed.