Extracellular pH Dynamically Controls Cell Surface Delivery of Functional TRPV5 Channels

Abstract

Extracellular pH has long been known to affect the rate and magnitude of ion transport processes among others via regulation of ion channel activity. The Ca²⁺-selective transient receptor potential vanilloid 5 (TRPV5) channel constitutes the apical entry gate in Ca²⁺-transporting cells, contributing significantly to the overall Ca²⁺ balance. Here, we demonstrate that extracellular pH determines the cell surface expression of TRPV5 via a unique mechanism. By a comprehensive approach using total internal reflection fluorescence microscopy, cell surface protein labeling, electrophysiology, ⁴⁵Ca²⁺ uptake assays, and functional channel recovery after chemobleaching, this study shows that upon extracellular alkalinization, a pool of TRPV5-containing vesicles is rapidly recruited to the cell surface without collapsing into the plasma membrane. These vesicles contain functional TRPV5 channels since extracellular alkalinization is accompanied by increased TRPV5 activity. Conversely, upon subsequent extracellular acidification, vesicles are retrieved from the plasma membrane, simultaneously resulting in decreased TRPV5 activity. Thus, TRPV5 accesses the extracellular compartment via transient openings of vesicles, suggesting that rapid responses of constitutive active TRP channels to physiological stimuli rely on vesicular “kiss and linger” interactions with the plasma membrane.

This work was supported by the Dutch Organization of Scientific Research (Zon-M_w 016.006.001, NWO-ALW 805.09.042), Human Frontiers Science Program (RGP32/2004), the European Science Foundation (EURYI), and the Dutch Kidney Foundation (C03.6017) and a grant of the van Walree Fund from the Royal Dutch Academy of Sciences to support the work visit of T. T. Lambers to the lab of D. Clapham.