Dashed lines are SE. Open in a separate window Fig. GdCl3 and 50 M SKF-96365. After incubation of IMCD with 1 nM AVP in Ca2+-free medium, software of extracellular Ca2+ also induced Ca2+ influx, which was sensitive to GdCl3 and SKF-96365. In summary, our observations are consistent with the notion that AVP-induced Ca2+ oscillations in IMCD are mediated from the interplay of Ca2+ launch from RyRs and a Ca2+ influx mechanism involving nonselective cation channels that resembles SOCE. = 0. Packed square shows that mean value is definitely significantly different from the baseline before AVP exposure Itga1 ( 0.05). 0.05). Dashed lines are SE. Open in a separate windowpane Fig. 4. Adobe flash photolysis of caged inositol 1,4,5-trisphosphate (IP3) Thymidine in IMCD. 0.05). and by caged cAMP and caged cADPR from Fig. 2. Dashed lines are SE. Effects of photoreleased cyclic ADP-ribose and IP3 in IMCD. We have demonstrated previously (8, 45) that AVP-induced Ca2+ mobilization is dependent on ryanodine-sensitive Ca2+ stores. To further investigate the RyR-dependent Ca2+ oscillations, IMCDs were loaded with NPE-caged cADPR, an endogenous agonist of RyR, by a reversible permeabilization protocol using streptolysin-O (50). Photorelease of cADPR with 60 UV laser pulses delivered over 2 s induced a rapid increase in cytosolic Ca2+ followed by [Ca2+]i oscillations. The mean normalized time program for fluo-4 emission is Thymidine definitely demonstrated in Fig. 2and and 0.05). Dashed lines are SE. To investigate the involvement of IP3-sensitive Ca2+ stores in mediating Ca2+ oscillations, the effects Thymidine of photolytic launch of IP3 in fluo-4 emission were examined in IMCD. The mean normalized time courses of changes in fluo-4 emission in responding to adobe flash Thymidine photolysis of caged IP3 are demonstrated in Fig. 4 0.05), which suggested that IP3 may contribute in part to the initial spike of the AVP-induced intracellular Ca2+ release or xestospongin C may have other effects in the intracellular Ca2+ stores in addition to blocking IP3Rs (9). Store-operated Ca2+ access in IMCD. Our earlier study (45) showed that removal of extracellular Ca2+ did not prevent the initial rise of [Ca2+]i but inhibited the sustained oscillations induced by AVP in IMCD. This suggested that access of extracellular Ca2+ was required to maintain the AVP-induced Ca2+ oscillations. Ca2+ access was not mediated by L-type voltage-gated Ca2+ channel, as nifedipine (10 M) did not inhibit AVP-induced Ca2+ oscillations (Fig. 5, and 0.05) in the presence of 50 M SKF-96365 and to 1.61 0.06 (88 cells/5 tubules, 0.05) in the presence of 1 M GdCl3. SKF-96365 and a low concentration of Gd3+ are two popular antagonists for SOCE and nonselective cation channels. These results indicated that depletion of intracellular Ca2+ stores induced SOCE in IMCD. Open in a separate windowpane Fig. 6. Activation of store-operated Ca2+ access (SOCE) by thapsigargin in IMCD. IMCDs were incubated with 20 M thapsigargin Thymidine in the absence of extracellular Ca2+ for 25 min. Subsequent addition of 2 mM Ca2+ to the peritubular perfusate resulted in a rapid extracellular Ca2+ access (126 cells/7 tubules), which was inhibited by GdCl3 (88 cells/5 tubules) and 50 M SKF-96365 (33 cells/3 tubules). The Ca2+ access induced by readdition of bath Ca2+ was absent without thapsigargin incubation (62 cells/5 tubules). Packed symbols indicate that mean value is significantly different from the equivalent data point in the control ( 0.05). Dashed lines are SE. To determine whether AVP could result in extracellular Ca2+ influx related to that induced by thapsigargin, IMCD was incubated with 1 nM AVP in Ca2+-free medium for 30 min. Readdition of 2 mM Ca2+ to the peritubular perfusate produced a rapid Ca2+ access (Fig. 7). The mean normalized fluo-4 fluorescence in the peaks of Ca2+ access was significantly reduced from 2.72 0.09 (135 cells/8 tubules) to 1 1.32 0.11 (35 cells/3 tubules, 0.05) in the presence of 50 M SKF-96365 and to 1.89 0.07 (54 cells/4 tubules, 0.05) in the presence of 1 M GdCl3. Open in a separate.