Oscillating Cortical Thick Ascending Limb Cells at the Juxtaglomerular Apparatus

Abstract

While studying the intracellular calcium dynamics in cells of the macula densa, the observation was made that tubular epithelial cells located near the macula densa and associated with the renal arterioles exhibit spontaneous Ca 2ϩ oscillations. In this study, the cortical thick ascending limb-distal tubule, with attached glomerulus, was isolated and perfused. At a low luminal sodium chloride concentration, Ca 2ϩ oscillations at a frequency of 63 mHz were observed in tubular cells that were within 100 m of the macula densa plaque using four-dimensional multiphoton microscopy and wide-field fluorescence microscopy with fura-2. The Ca 2ϩ oscillations were absent in the macula densa cells. Spontaneous oscillations in basolateral membrane potential suggested that Ca 2ϩ oscillations occurred, at least in part, through depolarization-induced increases in Ca 2ϩ entry. The amplitude of these Ca 2ϩ oscillations was significantly enhanced by the activation of the Ca 2ϩ -sensing receptor. Increasing the luminal sodium chloride concentration or luminal flow resulted in a significant increase in both the amplitude of Ca 2ϩ oscillations and the intracellular Ca 2ϩ concentration in perimacular cortical thick ascending limb cells. In addition, luminal furosemide attenuated the [NaCl] L -dependent changes in intracellular Ca 2ϩ concentration, but hydrochlorothiazide had no effect. These findings demonstrate that tubular epithelial cells at the perimeter of the macula densa exhibit spontaneous oscillations in intracellular Ca 2ϩ concentration, enhanced by tubular flow and luminal sodium chloride. These oscillatory patterns may play a role in juxtaglomerular signaling.

Tubuloglomerular feedback mechanisms in nephron segments beyond the macula densa

“…Interestingly, scavenging extracellular ATP did not affect the oscillations (unpublished observations). Similar to its action on tubuloglomerular feedback responses [26], furosemide blocked the [NaCl] L -dependent changes in intracellular Ca 2þ oscillations in the early distal tubule, whereas hydrochlorothiazide had no effect [27 ]. This suggests that the Na þ 2Cl À :K þ cotransporter and not the Na þ :Cl À cotransporter mediates the sensing of the tubular environment.…”

Electrotonic vascular signal conduction and nephron synchronization

“…The model that simulates the TGF oscillation is based on the assumption that the negative feedback structure is the only source of the oscillation (11,12). Recently, sustained oscillations in intracellular Ca 2ϩ have been reported in podocytes and in cells of the cortical thick ascending limb epithelium (16,26). The Ca 2ϩ oscillations have frequencies similar to those found for tubular pressure and flow, but their functional significance remains to be established and are not included in the present model.…”

ATP as a mediator of macula densa cell signalling

“…Also, as shown in Fig. 3, cytosolic calcium regulation in macula densa cells is unusual [45,108]. Basal levels of calcium concentration are remarkably low compared with those of the surrounding TAL cells.…”