The effects of streaming potential modeled electric fields on bovine aortic endothelial cells

Abstract

Bovine aortic endothelial cells (BAECs) respond to blood flow by modulation of membrane potential and nitric oxide production ([NO]). Shearing forces, mechanically generated by blood flow, have a well-described influence on BAEC biology. However, blood flow simultaneously generates an electrical streaming potential by inducing charge separation along the vascular wall. This study investigated the role of the streaming potential as a factor in BAEC biology. Within a laminar flow chamber, both shearing force and an electrical signal were recorded [0, 0.35, 1.2, 2.0 N-m^-2 ; 0-2 V-m^-1 DC/300 mV-m^-1 AC]. At constant flow onset, a membrane potential sensitive fluorescent probe, DiBAC4(3), demonstrated BAEC hyperpolarization (-8 mV, maximal at <100 secs) with depolarization back to baseline in 200 seconds. When the streaming potential was neutralized, flow onset induced a prolonged hyperpolarization (~4-6 mV, maximal at <100 seconds) without subsequent depolarization. Application of an isolated streaming potential modeled field caused a ~2 mV depolarization. Using channel blocking agents, the streaming potential effect was attributed to a flow-sensitive calcium-activated chloride channel. A nitric oxide specific fluorescent probe, DAF-2, showed [NO] to be proportional to the shearing force. When the streaming potential was neutralized, [NO] was potentiated. The pulsatile electrokinetic vascular streaming potential (EVSP), found in vivo, can be modeled mathematically by oscillating electric fields. EVSP applied to BAECs caused membrane depolarization (up to 7 mV, p < 0.05) proportional to field frequency, but not field strength. Without fluid flow, ATP stimulation of BAECs was needed to elevate [NO] into an observable range. ATP stimulated [NO] demonstrated early logarithmic (first 30 min) and subsequent (30 min to 2 hrs) exponential relationships. Simultaneous EVSP and ATP stimulation showed increased [NO] greater than ATP stimulation alone. Studies performed in ±Ca2+ media and with calcium channel blockade demonstrated effects proportional to EVSP field strength and frequency on these processes. In summary, our results provide evidence for a role of the streaming potential in the flow response of BAECs, previously attributed only to mechanical shearing forces. Streaming potential-modeled fields induced frequencydependent depolarization in BAECs. These fields decreased flow-induced [NO], and potentiated ATP-induced [NO].