Role of hβ[sub 1] 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[sup 2+]-activated K[sup +] 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[sub 1-4]). We used patch-clamp analysis to determine the influence of hβ[sub 1], hβ[sub 2], and hβ[sub 4] on activation of human mesangial BK by cGMP kinase. We found that HEK 293 cells, coexpressing human (h) Sloα with either hβ[sub 1] or hβ[sub 2], contained single BK currents activated by db-cGMP in cellattached patches. However, recombinant BK were not activated by db-cGMP when hSloα was expressed alone or with hβ[sub 4]. DNA-RNA hybridization revealed that mesangial cells contained mRNA for hβ[sub 1] but not hβ[sub 2] or hβ[sub 4]. The BK response to db-cGMP was decreased when hβ[sub 1] antisense but not scrambled oligonucleotides were incorporated into mesangial cells. Western blot analysis showed that hβ[sub l] antisense oligonucleotide inhibited the amount of hβ[sub 1]-V5 fusion protein expressed in HEK 293 cells by ∼50%. These results show that mesangial cells contain hβ[sub 1], a BK accessory protein, which confers activation of BK by cGMP kinase. [ABSTRACT FROM AUTHOR]