Key result
In cultured human glomerular mesangial cells, depletion of intracellular Ca2+ stores with thapsigargin evoked a significant increase in intracellular calcium (147 ± 16 nM vs 6 nM control).
Human glomerular mesangial cells exhibit an electrogenic Ca2+ influx pathway and small-conductance divalent-selective channels consistent with highly abundant store-operated Ca2+ channels.
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Demonstrates store-operated Ca2+ entry in cultured mesangial cells; leaves open any role in glomerular disease.
Experiments were performed to identify the biophysical properties of store-operated Ca2+channels (SOC) in cultured human glomerular mesangial cells (MC). A fluorometric technique (fura 2) was utilized to monitor the change in intracellular calcium concentration ([Ca2+]i) evoked by elevating external [Ca2+] from 10 nM to 1 mM (Δ[Ca2+]). Under control conditions, Δ[Ca2+] averaged 6 nM and was unaffected by elevating bath [K+]. After treatment with 1 μM thapsigargin to deplete the intracellular Ca2+store, the change in [Ca2+]i(Δ[Ca2+]th) averaged 147 ± 16 nM. In thapsigargin-treated MC studied under depolarizing conditions (75 mM bath K+), Δ[Ca2+]thwas 45 ± 7 nM. The Δ[Ca2+]thresponse of thapsigargin-treated cells was inhibited by La3+(IC50= 335 nM) but was unaffected by 5 μM Cd2+. In patch clamp studies, inward currents were observed in cell-attached patches with either 90 mM Ba2+or Ca2+in the pipette and 140 mM KCl in the bathing solution. The single-channel conductance was 2.1 pS with Ba2+and 0.7 pS with Ca2+. The estimated selectivities were Ca2+> Ba2+>> K+. These channels were sensitive to 2 μM La3+, insensitive to 5 μM Cd2+, and voltage independent, with an average channel activity ( NPo) of 1.02 at command potential (− Vp) ranging from 0 to −80 mV. In summary, MC exhibited an electrogenic Ca2+influx pathway that is suggestive of Ca2+entry through SOC, as well as a small-conductance divalent-selective channel displaying biophysical properties consistent with SOC. Based on estimates of whole cell Ca2+influx derived from our data, we conclude that SOC with low single-channel conductance must be highly abundant in MC to allow significant capacitative Ca2+entry in response to depletion of the intracellular store.
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Ma et al. (2000) studied Cultured human glomerular mesangial cells. Thapsigargin vs. Control conditions was evaluated on Change in intracellular calcium concentration (Δ[Ca2+]i). In cultured human glomerular mesangial cells, depletion of intracellular Ca2+ stores with thapsigargin evoked a significant increase in intracellular calcium (147 ± 16 nM vs 6 nM control).
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