Vascular Reactivity Profile of Novel K_Ca3.1‐Selective Positive‐Gating Modulators in the Coronary Vascular Bed

Abstract

Opening of intermediate-conductance calcium-activated potassium channels (KCa3.1) produces membrane hyperpolarization in the vascular endothelium. Here, we studied the ability of two new KCa3.1-selective positive-gating modulators, SKA-111 and SKA-121, to (1) evoke porcine endothelial cell KCa3.1 membrane hyperpolarization, (2) induce endothelium-dependent and, particularly, endothelium-derived hyperpolarization (EDH)-type relaxation in porcine coronary arteries (PCA) and (3) influence coronary artery tone in isolated rat hearts. In whole-cell patch-clamp experiments on endothelial cells of PCA (PCAEC), KCa currents evoked by bradykinin (BK) were potentiated ≈7-fold by either SKA-111 or SKA-121 (both at 1 μM) and were blocked by a KCa3.1 blocker, TRAM-34. In membrane potential measurements, SKA-111 and SKA-121 augmented bradykinin-induced hyperpolarization. Isometric tension measurements in large- and small-calibre PCA showed that SKA-111 and SKA-121 potentiated endothelium-dependent relaxation with intact NO synthesis and EDH-type relaxation to BK by ≈2-fold. Potentiation of the BK response was prevented by KCa3.1 inhibition. In Langendorff-perfused rat hearts, SKA-111 potentiated coronary vasodilation elicited by BK. In conclusion, our data show that positive-gating modulation of KCa3.1 channels improves BK-induced membrane hyperpolarization and endothelium-dependent relaxation in small and large PCA as well as in the coronary circulation of rats. Positive-gating modulators of KCa3.1 could be therapeutically useful to improve coronary blood flow and counteract impaired coronary endothelial dysfunction in cardiovascular disease.

Endothelial KCa1.1 and KCa3.1 channels mediate rat intrarenal artery endothelium‐derived hyperpolarization response

“…A remaining voltage‐independent K + current was found to be sensitive to the K Ca 2.3 blocker, UCL 1684, revealing co‐activation of K Ca 2.3. Both, TRAM‐34‐ and UCL 1684‐sensitive currents, were voltage independent and very similar to the SKA‐121‐induced currents previously reported in isolated ECs from porcine coronary arteries 35 . In RIAECs, K Ca 2.3‐current component appears, however, smaller, indicating lower protein expression levels or less Ca 2+ ‐dependent activation by ACh.…”

“…A less strong activation to ACh and subsequent EDH-type vasodilation has been attributed to distinct intracellular localization, with K Ca 3.1 sensing preferentially Ca 2+ released from nearby internal stores. [7][8][9] Together, the electrophysiological and pharmacological properties of the different K Ca currents (Figure 4) found in native RIAECs show the typical fingerprints of K Ca 3.1, K Ca 2.3 35,36 and of K Ca 1.1, which so far has not been identified as endothelial channel in the rat renal interlobar arteries.…”

“…Both, TRAM-34-and UCL 1684-sensitive currents, were voltage independent and very similar to the SKA-121-induced currents previously reported in isolated ECs from porcine coronary arteries. 35 In RIAECs, K Ca 2.3-current component appears, however, smaller, indicating lower protein expression levels or less Ca 2+ -dependent activation by ACh. A less strong activation to ACh and subsequent EDH-type vasodilation has been attributed to distinct intracellular localization, with K Ca 3.1 sensing preferentially Ca 2+ released from nearby internal stores.…”

“…Rat intrarenal artery endothelial cells (RIAECs) were isolated from rat kidneys as described previously. 35,46 In brief, intrarenal arteries were cut open longitudinally and incubated in trypsin/EDTA (0.25%/0.02%) in PBS without Ca 2+ / Mg 2+ (Biochrom KG, Berlin, Germany) for 30 minutes at 37°C. Subsequently, EC were scraped and aspirated from the luminal surface and seeded on a µ-Dish 35 mm low (ibidi GmbH, Martinsried, Germany).…”

“…Ca 2+ was present at the mentioned concentration in the pipette solution to activate K Ca currents. 35 Some recordings were performed using a pipette solution of the same composition but without CaCl 2 .…”