AQP can shape the pattern of calcium transients induced by store operated calcium entry.

PIZZONI ALEJANDRO; RAJOY JUANA; DI GIUSTO GISELA; RIVAROLA VALERIA; CAPURRO CLAUDIA; FORD PAULA

salto

Congreso; Latin American Crosstalk In Biophysics And Physiology?; 2015

Seccional Biofísica de la Sociedad Uruguaya de Biociencias en conjunto con la Sociedad Argentina de Biofísica

The transient receptor potential channel 4 (TRPV4) is a mechano-sensitive ion channel whose function is important for cell volume regulation. Frequently, cellular responses to changes in osmolality involve TRPV4-mediated elevation of intracellular Ca2+ and consequent activation of calcium- activated potassium channels (KCa)1. Activation of one or more of these channels will result in membrane hyperpolarization. This will increase the driving force for intracellular Ca2+ increase activating further KCa in a positive feedback loop and it could have consequences in store operated calcium entry (SOCE)2. We have previously demonstrated, in renal cells, a functional interaction between the water channel AQP2 and TRPV4 in sensing osmotic stress that leads to the activation of regulatory volume mechanisms3. The aim of our work was to study the influence of changes of the membrane potential in SOCE transients produced in the renal cells depending on both the presence of AQP2 and/or TRPV4 activation. Fura-2 dye was used to monitor [Ca2+]i and Dibac4(3) was used to monitor Vm changes in two renal cell lines; one not expressing AQP2 (WT-RCCD1) and another one transfected with AQP2 (AQP2-RCCD1). We found that using a specific activator of TRPV4 (4α-PDD, 10 µM) WT cells depolarize and AQP2 hyperpolarize. This hyperpolarization does not occur in the presence of apamin (300 nM) indicating that in AQP2 cells activation of TRPV4 leads to the activation of one KCa, SK3. Using thapsigargin (1 µM) in a classic protocol for study SOCE, we found that the activation of TRPV4 increases SOCE in cells expressing AQP2 compared to WT ones. These results suggest an influence of AQP2-TRPV4-SK3 in maximizing SOCE transients. However this response is probably not due only to an increased driving force since when cells were depolarized with high extracellular K+ during SOCE, WT significantly decreased calcium influx and AQP2 was modestly affected.