Mechanically‐induced intercellular calcium waves in renal medullary interstitial cells

Abstract

In addition to providing structural support, renomedullary interstitial cells (RMIC) are thought to play an active physiological role in regulating renal medullary function. RMICs have been shown to have contractile properties, however, the cellular and molecular mechanisms of this action remain unknown. We aimed to identify the existence of molecular elements of an intercellular calcium wave in cultured rat RMICs using Fluo‐4/Fura red and confocal fluorescence microscopy. RMICs expressed connexins (Cx) Cx30 and Cx45 and P2X4 and P2Y2 purinergic receptors measured by RT‐PCR and immunohistochemistry. Mechanical stimulation of a single RMIC caused a 4±0.2‐fold increase in [Ca2+]i (n=45) which was propagated throughout the monolayer (16 ± 1.2 um/s) in a regenerative manner (without decrement of amplitude, kinetics, and speed) over distances >800 um. The gap junction uncoupler 18a‐glycyrrhetinic acid (18a‐GA, 25 uM), breakdown of extracellular ATP (apyrase and hexokinase, 50 U/mL each), or P2 receptor inhibition (suramin, 50 uM) all decreased the speed and D[Ca2+]i of the calcium wave. Physical contact between cells was not required for calcium wave propagation. These studies suggest that mechanosensitive, ATP‐releasing Cx hemichannels and cell‐to‐cell purinergic signaling are key molecular elements of the RMIC calcium wave, which may serve an important role in RMIC‐mediated renal medullary function.