Nitric oxide (NO) synthesized by vascular endothelial cells is a potent vasodilator substance. The actions of NO extend well beyond its vasodilatory properties, and increasingly, NO has been recognized as an important signal for intercellular and intracellular communication. Recently, NO has been implicated in the regulation of vascular and bloodbrain barrier permeability. NO has also been shown to modulate ion channels in excitable cells, thus affecting neuronal firing. We report the results

more »

... patch-clamp experiments that show a modulatory action of NO as well as cGMP and cAMP on a hyperpolarization-activated current (Iha) carried by both Na+ and K' ions in blood-brain barrier endothelial cells. lha was recorded in cells dialyzed with 0.2 mmol/L GTP-y-S to inhibit a large inwardly rectifying potassium current. This ionic current and its modulation by NO may play a role in the regulation of the transport of ions, nutrients, and other molecules to the brain and serve as an integral part of the blood-brain barrier. The modulation of Iha by a cyclic guanosine nucleotide may also explain previous reports suggesting a role for NO in the regulation of blood-brain barrier function. (Circ Res. 1994;75:528-538.) plated on poly-D-lysine-coated dishes to remove nonendothelial cells. Nonadherent rat cerebral microvascular EC clusters were then transferred to fibronectin-coated dishes and maintained in DMEM containing 15% equine plasma-derived serum, 4% fetal bovine serum, 50 ,ug/mL heparin, 100 Ag/mL EC growth supplement, 1 mmol/L pyruvate, 2 mmol/L glutamine, nonessential amino acids, vitamins, 100 U/mL penicillin, 100 ,ug/mL streptomycin, and 0.25 ,tg/mL Fungizone. These cells were identified as ECs on the basis of positive immunoreactivity for factor VIII antigen and specific uptake of by guest on July 22, 2018 http://circres.ahajournals.org/ Downloaded from When the nonhydrolyzable GTP analogue GTP-y-S (0.2 mmol/L, n=40) was added to the recording pipette, the total whole-cell current size as well as the timedependent inactivation of the IIR was greatly reduced, unmasking another underlying 'ha (compare Fig 2A1 and 2A2 ). Abolishment of IIR by GTP-y-S has been previously reported in human dermal fibroblasts, guinea pig chromaffin cells, and porcine cerebral ECs.16,22 24 A typical current-voltage relation for the total whole-cell current as measured after washout of IIR is shown in Fig