Figure 3.

MICU1 Acts as an Activator of MCU

(A and B) In vitro expressed MCU activity was recorded in sodium-gluconate containing 5 mM EDTA (10 pM free calculated [Ca²⁺]) at −40 mV V_cis. Addition of MICU1 to either the cis or the trans side did not cause significant change in channel behavior nor an increase in open probability.

(A) Representative current traces.

(B) Amplitude histograms were obtained by analyses of 60 s long traces before and after addition of MICU1 to the cis side. Gaussian fits of the multipeak histogram (red), baseline current (yellow), and MCU current (green) were obtained using the Origin 7.5 program set (n = 3).

(C and D) In vitro expressed MCU was incorporated into a sodium-gluconate medium containing 1 μM Ca²⁺-gluconate and activity was monitored at −120 mV. Channel activity in this medium was detectable with much lower unitary current and open probability compared to the medium containing sodium and 5 mM EDTA. Left: activity recorded before addition of MICU1. Right: activity following addition (arrowhead in open probability histogram) of MICU1.

(C) Representative traces of the channel activity.

(D) Open probability as a function of time was monitored and measured for the indicated times.

See also Figure S3.