Large-conductance, calcium- and voltage-activated potassium (BKCa) channels play a crucial role in the regulation of membrane potential and contractility of pulmonary arterial smooth muscle cells (PASMCs). Under normal conditions, cAMP-elevating agents activate BKCa channels in PASMCs and cause vasodilatation, while inhibition (closing) of BKCa channels leads to pulmonary vasoconstriction which has been considered as one of the key factors that contribute to the development of pulmonary hypertension. Clinical evidence suggests that there is a higher chance of developing pulmonary hypertension in patients with diabetes. However, little information is known about the expression and potential signaling mechanism of BKCa channels in the pulmonary vasculature in the diabetic state. Therefore, we assessed BKCa channel expression and signaling regulation in PASMCs from normal and diabetic pigs and human cell lines. Western blots showed that both normal and diabetic pig PASMC express both BKCa channel α-subunits and β1-subunits with a greater expression of α- subunits in diabetic PASMC. Electrophysiological studies using inside-out cell patches from normal PASMC also demonstrated that BKCa channels were activated by 100μM Ca2+, which was blocked by 1mM tetraethylammonium (TEA, a selective BKCa channel inhibitor at this concentration). In cell-attached patches, forskolin (10μM), an activator of adenylyl cyclase which increases cAMP concentration, increased BKCa channel activity significantly in control PASMC. Subsequently, cAMP generation was measured in both control and diabetic PASMC. Basal cAMP levels in diabetic pig PASMC were lower than in control PASMC, and forskolin (10μM) increased cAMP generation to a lesser extent in diabetic PASMC compared to control PASMC. Similar results were observed and confirmed in human PASMC lines as well. Collectively, these results indicate that signaling pathways involving BKCa channels and cAMP are altered in diabetic PASMCs, which suggests potential differences in pulmonary vasoreactivity between the normal and diabetic states.
Available at: http://works.bepress.com/shu_zhu/14/