Figure 2. Endogenous I_CRAC is unmasked in HSG cells when TRPC1 function is suppressed by expression of STIM1(⁶⁸⁴EE⁶⁸⁵).

HSG cells were transfected with plasmids encoding WT-STIM1, STIM1(⁶⁸⁴EE⁶⁸⁵), or TRPC1(⁶³⁹KK⁶⁴⁰). (A) Fura-2 fluorescence measurements in the cells indicated. Right panel shows average values for internal release and calcium influx (calculated as described for Figure 1). (B) Whole cell patch clamp measurements in HSG cells expressing STIM1(⁶⁸⁴EE⁶⁸⁵); left panel shows development of current with Tg in normal external solution (current recorded at −80 mV is shown) and right panel shows the I–V relationship of the current. Fura-2 (C, E) or patch clamp (D) measurements in HSG cells transfected with SOAR alone or together with shTRPC1 or siOrai1 (as indicated in each figure). Ca²⁺ was added to cells maintained in Ca²⁺-free medium (C, left panel) and average increase in fura-2 fluorescence, reflecting basal Ca²⁺ entry, is shown by the bar graphs in the inset (** indicates values that are significantly different, p<0.01, from other values but not from each other). (D) Spontaneously activated current recorded in SOAR-expressing HSG cells when 10 mM BAPTA was included in the pipette solution (see Materials and Methods for details). Inset shows the I_CRAC-like I–V relationship of the current. (E) [Ca²⁺]_i measurements in Tg-treated HSG cells expressing SOAR or SOAR+shTRPC1. Inset shows average values obtained under these conditions. Note that basal Ca²⁺ entry in SOAR-expressing cells is similar to that seen in Tg-treated cells expressing SOAR+shTRPC1 (compare red traces in C and E). ** indicates values that are significantly different from control values (p<0.01, data obtained from at least five different experiments and include at least 50–60 cells for each condition).