Aldosterone transcriptionally regulates large conductance K+ channel β1 (BKβ1)‐ subunit specific mRNA abundance in rat distal colon (LB845)

Abstract

Background: Large conductance K+ (BK) channels localized on the apical membranes mediate cAMP and aldosterone (“aldo”) activated K+ secretion in rat distal colon. BK channels composed of α (BKα) and β (BKβ) subunits. Four different BKβ (BKβ1, BKβ2, BKβ3 and BKβ4) isoforms have been shown expressed in tissue specific pattern. Recent studies have shown “aldo” transcriptionally up‐regulates BKα‐subunit. The identity of BKβ isoform and its regulation by “aldo” is not known in rat distal colon. Aim:This study was aimed: 1) to identify the BKβ isoform; and 2) to demonstrate whether BKβ subunit also transcriptionally regulated by “aldo” in rat distal colon. Methods: “Aldo” rats (Sprague‐Dawley, 200 ‐ 220 g) were produced by feeding Na‐freed diet ad libitum for 6 ‐ 7 days. Total RNA was purified from epithelial cells isolated form rat proximal and distal colon. BKβ isoform specific fragments were amplified using isoform specific primers and polymerase chain reaction (PCR). Quantitative RT‐PCR (RT‐qPCR) analyses were performed to quantify the expression level of BKβ.isoform in “aldo” rat distal colon. Results: PCR amplified BKβ1, but not BKβ2, BKβ3 and BKβ4 isoform specific fragments in both proximal and distal colon. RT‐qPCR analyses revealed that similar to BKα‐subunit, BKβ1‐subunit specific mRNA expression also enhanced by 3.5‐fold in “aldo” rat distal colon. The P‐values for BKβ1 subunit was less than 0.05 thus indicating a significant change at a 95% confidence. BKβ1‐subunit specific mRNA level is not altered in “aldo” proximal colon. Conclusions: Rat colonic BK channel consists of BKβ1 isoform; and 2) “Aldo” transcriptionally up regulates both BKα‐ and BKβ1‐subunits in distal, but not proximal colon.Grant Funding Source: West Virgina University Intramural award