Role of hβ₁ in activation of human mesangial BK channels by cGMP kinase

In vascular smooth muscle and glomerular mesangial cells, relaxing agents such as nitric oxide and atrial natriuretic peptide activate large - conductance Ca²⁺-activated K⁺ channels (BK) via the cGMP kinase pathway. BK are composed of pore-forming α-subunits, encoded by the slopoke gene (Slo), and one of four cell-specific accessory β-subunits (hβ_1-4). We used patch-clamp analysis to determine the influence of hβ₁, hβ₂, and hβ₄ on activation of human mesangial BK by cGMP kinase. We found that HEK 293 cells, coexpressing human (h) Sloα with either hβ₁ or hβ₂, contained single BK currents activated by db-cGMP in cell-attached patches. However, recombinant BK were not activated by db-cGMP when hSloα was expressed alone or with hβ₄. DNA-RNA hybridization revealed that mesangial cells contained mRNA for hβ₁ but not hβ₂ or hβ₄. The BK response to db-cGMP was decreased when hβ₁ antisense but not scrambled oligonucleotides were incorporated into mesangial cells. Western blot analysis showed that hβ₁ antisense oligonucleotide inhibited the amount of hβ₁-V5 fusion protein expressed in HEK 293 cells by ∼50%. These results show that mesangial cells contain hβ₁, a BK accessory protein, which confers activation of BK by cGMP kinase.