Dynamics of mitochondrial Ca2{+} uptake in MICU1-knockdown cells

MICU1 is an important regulator of the mitochondrial Ca2+-uniporter (MCU) that has been recently shown to act as a gatekeeper of MCU at low cytosolic [Ca2+] ([Ca2+]c). We have studied here in detail the dynamics of MCU activity after shRNA-knockdown of MICU1 and we find several new interesting properties. In MICU1-knockdown cells, the rate of mitochondrial Ca2+-uptake was largely increased at low [Ca2+]c (<2µM), but it was decreased at high [Ca2+]c (>4µM). In the 2-4µM range, a mixed behavior was observed, where mitochondrial Ca2+-uptake started earlier in the MICU1-silenced cells but slower than in the controls. Sensitivity of Ca2+-uptake to ruthenium red and Ru360 was similar at both high and low [Ca2+]c, indicating that the same Ca2+-pathway was operating in both cases. The increased Ca2+-uptake rate observed at [Ca2+]c below 2µM was transient and became inhibited during Ca2+-entry. Development of this inhibition was slow, required 5 min for completion, and was hardly reversible. Therefore, MICU1 acts both as a MCU gatekeeper at low [Ca2+]c and as a cofactor necessary to reach the maximum Ca2+-uptake rate at high [Ca2+]c. Moreover, in the absence of MICU1, MCU becomes sensitive to a slow-developing inhibition that requires prolonged increases in [Ca2+]c in the low micromolar range.

Source: BJ Cell - December 9, 2013 Category: Biochemistry Authors: S de la Fuente, J Matesanz-Isabel, R I. Fonteriz, M Montero, J Alvarez Tags: BJ Cell Source Type: research