β-adrenergic receptor (βAR) activation promotes relaxation of both vascular and airway smooth muscle cells (VSMCs and ASMCs, respectively), though the signaling mechanisms have not been fully elucidated. We previously found that the activity of Kv7.5 voltage-activated potassium channels in VSMCs is robustly enhanced by activation of βARs via a mechanism involving protein kinase A (PKA)-dependent phosphorylation. We also found that enhancement of Kv7 channel activity in ASMCs promotes airway relaxation. Here we provide evidence that Kv7.5 channels are natively expressed in primary cultures of human ASMCs and that they conduct currents which are robustly enhanced in response to activation of the βAR/cyclic adenosine monophosphate (cAMP)/PKA pathway. MIT Scansite software analysis of putative PKA phosphorylation sites on Kv7.5 identified 8 candidate serine or threonine residues. Each residue was individually mutated to an alanine to prevent its phosphorylation and then tested for responses to βAR activation or to stimuli that elevate cAMP levels. Only the mutation of serine 53 (S53A), located on the amino terminus of Kv7.5, significantly reduced the increase in Kv7.5 current in response to these stimuli. A phospho-mimic mutation (S53D) exhibited characteristics of βAR-activated Kv7.5. Serine-to-alanine mutations of 6 putative PKA phosphorylation sites on the Kv7.5 C-terminus, individually or in combination, did not significantly reduce the enhancement of the currents in response to forskolin treatment (to elevate cAMP levels). We conclude that phosphorylation of S53 on the amino terminus of Kv7.5 is essential for PKA-dependent enhancement of channel activity in response to βAR activation in vascular and airway smooth muscle cells.

Kv7 potassium channels have recently been found to be expressed and functionally important for relaxation of airway smooth muscle. Previous research suggests that native Kv7 currents are inhibited following treatment of freshly isolated airway smooth muscle cells with bronchoconstrictor agonists, and in intact airways inhibition of Kv7 channels is sufficient to induce bronchiolar constriction. However, the mechanism by which Kv7 currents are inhibited by bronchoconstrictor agonists has yet to be elucidated. In the present study, native Kv7 currents in cultured human trachealis smooth muscle cells (HTSMCs) were observed to be inhibited upon treatment with histamine; inhibition of Kv7 currents was associated with membrane depolarization and an increase in cytosolic Ca ([Ca]). The latter response was inhibited by verapamil, a blocker of L-type voltage-sensitive Ca channels (VSCCs). Protein kinase C (PKC) has been implicated as a mediator of bronchoconstrictor actions, although the targets of PKC are not clearly established. We found that histamine treatment significantly and dose-dependently suppressed currents through overexpressed wild-type human Kv7.5 (hKv7.5) channels in cultured HTSMCs, and this effect was inhibited by the PKC inhibitor Ro-31-8220 (3 µM). The PKC-dependent suppression of hKv7.5 currents corresponded with a PKC-dependent increase in hKv7.5 channel phosphorylation. Knocking down or inhibiting PKCα, or mutating hKv7.5 serine 441 to alanine, abolished the inhibitory effects of histamine on hKv7.5 currents. These findings provide the first evidence linking PKC activation to suppression of Kv7 currents, membrane depolarization, and Ca influx via L-type VSCCs as a mechanism for histamine-induced bronchoconstriction.

The authors present the case of an elderly patient suffering from obstructive cardiomyopathy and bleeding colonic angiodysplasia. After treatment with propranolol, the bleeding stopped without recurrence.

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Elderly patients and patients with high NYHA class need close postoperative monitoring in the ICU. A short circulatory arrest and aortic clamp time do not extend the LOS in ICU or in the hospital.