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 Ca(2+)-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 (hbeta(1-4)). We used patch-clamp analysis to determine the influence of hbeta(1), hbeta(2), and hbeta(4) on activation of human mesangial BK by cGMP kinase. We found that HEK 293 cells, coexpressing human (h) Sloalpha with either hbeta(1) or hbeta(2), 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 hbeta(4). DNA-RNA hybridization revealed that mesangial cells contained mRNA for hbeta(1) but not hbeta(2) or hbeta(4). The BK response to db-cGMP was decreased when hbeta(1) antisense but not scrambled oligonucleotides were incorporated into mesangial cells. Western blot analysis showed that hbeta(1) antisense oligonucleotide inhibited the amount of hbeta(1)-V5 fusion protein expressed in HEK 293 cells by similar to50%. These results show that mesangial cells contain hbeta(1), a BK accessory protein, which confers activation of BK by cGMP kinase.