Low channel conductances in capillary endothelial cells of guinea pig cochlea contribute to the blood‐labyrinth‐barrier

The blood‐labyrinth‐barrier at the strial vascularis (SV) capillaries separates big physical (>100 mV) and chemical gradients between the intrastrial space and blood stream while maintains necessary metabolites exchanges. The mechanisms required to fulfill these functions remain poorly understood. Using whole‐cell and single channel recording techniques, we explored the channel mechanisms in the capillary endothelial cells (ECs) and pericytes (PCs) in acutely isolated SV capillary segments and in fully dispersed state. We found that 1) with physiological solutions in‐and‐out, SV ECs in segments had a membrane potential ~−30 mV, a C input ~28 pF and a R input ~ 510 MΩ (~10 pF and ~2 GΩ from isolated single cells). The I/V curve of ECs mostly exhibited a mild outward rectification at voltages positive to −40 mV, was slightly flattened by 4‐AP, TEA, and NFA, but not significantly changed by Ba 2+ , La 3+, nitrendipine, apamin, glipizide or 20 mM K + . 2) In contrast, PCs had a membrane potential ~−50 mV, a C input ~85 pF and a R input ~ 306 MΩ (~10 pF and ~450 MΩ for isolated single cells), and an I/V relation with prominent inward rectification at potentials <−60 mV. The rectification was enhanced by [K] o elevation and abolished by 0.1 mM Ba 2+ . 3) Both cell types showed 18β‐glycyrrhetinic acid‐sensitive electro‐coupling. 4) Cellattached and outside‐out patch recordings from ECs occasionally detected activities of ~50 pS K + ‐channels with very low open probability. We conclude that SV ECs normally express little active channels, resulting in high R input thus to economically preserve the highly positive endocochlear potential, whereas SV PCs appear as a regulatory element. Supported by NIH grant R01 DC004716 (ZGJ).