LRRC26 Is a Functional BK Channel Auxiliary γ Subunit in Arterial Smooth Muscle Cells

Rationale: Smooth muscle cell (myocyte) large-conductance calcium (Ca)(2+)-activated potassium (BK) channels are functionally significant modulators of arterial contractility. Arterial myocytes express both pore-forming BK alpha and auxiliary beta 1 subunits, which increase channel Ca2+ sensitivity. Recently, several leucine-rich repeat containing (LRRC) proteins have been identified as auxiliary. subunits that elevate the voltage sensitivity of recombinant and prostate adenocarcinoma BK channels. LRRC expression and physiological functions in native cell types are unclear. Objective: Investigate the expression and physiological functions of leucine-rich repeat containing protein 26 (LRRC26) in arterial myocytes. Methods and Results: Reverse transcription polymerase chain reaction and Western blotting detected LRRC26 mRNA and protein in cerebral artery myocytes. Biotinylation, immunofluorescence resonance energy transfer microscopy, and coimmunoprecipitation indicated that LRRC26 was located in close spatial proximity to, and associated with, plasma membrane BK alpha subunits. LRRC26 knockdown (RNAi) reduced total and surface LRRC26, but did not alter BK alpha or beta 1, proteins in arteries. LRRC26 knockdown did not alter Ca2+ sparks but reduced BK channel voltage sensitivity, which decreased channel apparent Ca2+ sensitivity and transient BK current frequency and amplitude in myocytes. LRRC26 knockdown also increased myogenic tone over a range (40-100 mm Hg) of intravascular pressures, and reduced vasoconstriction to iberiotoxin and vasodilation to NS1619, BK channel inhibitors and activators, respectively. In contrast, LRRC26 knockdown did not alter depolarization (60 mmol/L K+)-induced vasoconstriction. Conclusions: LRRC26 is expressed, associates with BK alpha subunits, and elevates channel voltage-and apparent Ca2+ sensitivity in arterial myocytes to induce vasodilation. This study indicates that arterial myocytes express a functional BK channel. subunit.