Effects of α1-adrenoceptor agonist phenylephrine on swelling-activated chloride currents in human atrial myocytes.

Swelling-activated chloride currents (ICl.swell) play an important role in cardiac electrophysiology and arrhythmogenesis. However, the regulation of these currents has not been clarified to date. In this research, we focused on the function of phenylephrine, an α1-adrenoceptor agonist, in the regulation of I(Cl.swell) in human atrial myocytes. We recorded I(Cl.swell) evoked by a hypotonic bath solution with the whole-cell patch-clamp technique. We found that I(Cl.swell) increased over time, and it was difficult to achieve absolute steady state. Phenylephrine potentiated I(Cl.swell) from -1.00 ± 0.51 pA/pF at -90 mV and 2.58 ± 1.17 pA/pF at +40 mV to -1.46 ± 0.70 and 3.84 ± 1.67 pA/pF, respectively (P < 0.05, n = 6), and the upward trend in ICl.swell was slowed after washout. This effect was concentration-dependent, and the α1-adrenoceptor antagonist prazosin shifted the dose-effect curve rightward. Addition of prazosin or the protein kinase C (PKC) inhibitor bisindolylmaleimide (BIM) attenuated the effect of phenylephrine. The PKC activator phorbol 12,13-dibutyrate (PDBu) activated I(Cl.swell) from -1.69 ± 1.67 pA/pF at -90 mV and 5.58 ± 6.36 pA/pF at +40 mV to -2.41 ± 1.95 pA/pF and 7.05 ± 6.99 pA/pF, respectively (P < 0.01 at -90 mV and P < 0.05 at +40 mV; n = 6). In conclusion, the α1-adrenoceptor agonist phenylephrine augmented I(Cl.swell), a result that differs from previous reports in other animal species. The effect was attenuated by BIM and mimicked by PDBu, which indicates that phenylephrine might modulate I(Cl,swell) in a PKC-dependent manner.