MitoBKCa channel is functionally associated with its regulatory ?1 subunit in cardiac mitochondria.

ABSTRACT: KEY POINTS:Association of plasma membrane BKCa channels with BK-? subunits shapes their biophysical properties and physiological roles; however, functional modulation of the mitochondrial BKCa channel (mitoBKCa ) by BK-? subunits is not established. MitoBKCa -? and the regulatory BK-?1 subunit associate in mouse cardiac mitochondria. A large fraction of mitoBKCa display properties similar to that of plasma membrane BKCa when associated with BK-?1 (left-shifted voltage dependence of activation, V1/2  = -55 mV, 12 µm matrix Ca2+ ). In BK-?1 knockout mice, cardiac mitoBKCa displayed a low Po and a depolarized V1/2 of activation (+47 mV at 12 µm matrix Ca2+ ) Co-expression of BKCa with the BK-?1 subunit in HeLa cells doubled the density of BKCa in mitochondria. The present study supports the view that the cardiac mitoBKCa channel is functionally modulated by the BK-?1 subunit; proper targeting and activation of mitoBKCa shapes mitochondrial Ca2+ handling. ABSTRACT:Association of the plasma membrane BKCa channel with auxiliary BK-?1-4 subunits profoundly affects the regulatory mechanisms and physiological processes in which this channel participates. However, functional association of mitochondrial BK (mitoBKCa ) with regulatory subunits is unknown. We report that mitoBKCa functionally associates with its regulatory subunit BK-?1 in adult rodent cardiomyocytes. Cardiac mitoBKCa is a calcium- and voltage-activated channel that is sensitive to paxilline with a large conductance for K+ of 300 pS. Additionally, mitoBKCa displays a high open probability (Po ) and voltage half-activation (V1/2  = -55 mV, n = 7) resembling that of plasma membrane BKCa when associated with its regulatory BK-?1 subunit. Immunochemistry assays demonstrated an interaction between mitochondrial BKCa -? and its BK-?1 subunit. Mitochondria from the BK-?1 knockout (KO) mice showed sparse mitoBKCa currents (five patches with mitoBKCa activity out of 28 total patches from n = 5 different hearts), displaying a depolarized V1/2 of activation (+47 mV in 12 µm matrix Ca2+ ). The reduced activity of mitoBKCa was accompanied by a high expression of BKCa transcript in the BK-?1 KO, suggesting a lower abundance of mitoBKCa channels in this genotype. Accordingly, BK-?1subunit increased the localization of BKDEC (i.e. the splice variant of BKCa that specifically targets mitochondria) into mitochondria by two-fold. Importantly, both paxilline-treated and BK-?1 KO mitochondria displayed a more rapid Ca2+ overload, featuring an early opening of the mitochondrial transition pore. We provide strong evidence that mitoBKCa associates with its regulatory BK-?1 subunit in cardiac mitochondria, ensuring proper targeting and activation of the mitoBKCa channel that helps to maintain mitochondrial Ca2+ homeostasis.

SUBMITTER: Balderas E 

PROVIDER: S-EPMC6690848 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature