Role of hbeta1 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 alpha-subunits, encoded by the slopoke gene (Slo), and one of four cell-specific accessory beta-subunits (hbeta1-4). We used patch-clamp analysis to determine the influence of hbeta1, hbeta2, and hbeta4 on activation of human mesangial BK by cGMP kinase. We found that HEK 293 cells, coexpressing human (h) Sloalpha with either hbeta1 or hbeta2, contained single BK currents activated by db-cGMP in cell-attached patches. However, recombinant BK were not activated by db-cGMP when hSloalpha was expressed alone or with hbeta4. DNA-RNA hybridization revealed that mesangial cells contained mRNA for hbeta1 but not hbeta2 or hbeta4. The BK response to db-cGMP was decreased when hbeta1 antisense but not scrambled oligonucleotides were incorporated into mesangial cells. Western blot analysis showed that hbeta1 antisense oligonucleotide inhibited the amount of hbeta1-V5 fusion protein expressed in HEK 293 cells by approximately 50%. These results show that mesangial cells contain hbeta1, a BK accessory protein, which confers activation of BK by cGMP kinase.