The calcium chelator BAPTA abrogates the AFPNN5353-induced calcium signature The increased [Ca2+]c in response to AFPNN5353 treatment could originate from extracellular and/or from intracellular Apoptosis Compound Library order Ca2+ stores, such as mitochondria, vacuoles, Selleck CA3 endoplasmic reticulum or the Golgi apparatus. To discriminate between the extracellular and intracellular source of the [Ca2+]c increase, we tested the influence of the Ca2+-selective membrane impermeable chelator BAPTA. On its own, BAPTA did not influence the resting level of [Ca2+]c in twelve h old A. niger cultures (Figure 4). However, a pretreatment of the samples with 10 mM BAPTA before
the addition of AFPNN5353 inhibited the protein-specific increase in [Ca2+]c resting CX5461 level (Figure 4). Interestingly, the elevated [Ca2+]c in response to a 40 min AFPNN5353-treatment dropped to the resting level immediately after the addition of 10 mM BAPTA (Figure 4), indicating that the AFPNN5353-induced elevation of the [Ca2+]c resting
level requires the continuous influx of extracellular Ca2+ and eventually results in loss of [Ca2+]c homeostasis. Figure 4 Effect of the extracellular chelator BAPTA on the AFP NN5353 induced [Ca 2+ ] c resting level. 10 mM BAPTA (final conc.) were applied 40 min before or 40 min after treatment with 20 μg/ml AFPNN5353. Samples without supplements were used as controls. SD (n = 6) was less than 10% of the values presented. Extracellular calcium ameliorates the AFPNN5353-induced rise in [Ca2+]c To decipher the observation that high external CaCl2 concentrations counteracted AFPNN5353 toxicity (Table 3), we monitored the effect of externally added Ca2+
on the AFPNN5353-induced Ca2+ signature. To this end, A. niger germlings were preincubated with 20 mM CaCl2 for 10 min before 20 μg/ml AFPNN5353 was added and the changes in the [Ca2+]c resting level were monitored over a time course of 60 min. This treatment resulted in a less pronounced rise of the [Ca2+]c resting level compared to samples without preincubation with CaCl2. In contrast, the presence of 20 mM Ribonucleotide reductase CaCl2 alone had no major effect on the intracellular [Ca2+]c resting level which resembled that of the control without AFPNN5353 (data not shown). The values of the [Ca2+]c resting levels of the last 10 min (50 to 60 min) measurement of AFPNN5353 treatment in the presence or absence of high Ca2+ concentration (20 mM versus 0.7 mM) are summarized in Table 4. The average of the [Ca2+]c of the controls which were not exposed to AFPNN5353 was 0.039 μM in the presence of 0.7 μM CaCl2 (standard condition) and 0.062 μM in the presence of 20 mM CaCl2. When AFPNN5353 was added, there was no significant elevation of the [Ca2+]c in high-Ca2+ medium (20 mM) (0.057 μM) whereas the [Ca2+]c rised to 0.146 μM at standard CaCl2 concentration (0.7 mM).