Effects of α1-Adrenoceptor Agonist Phenylephrine on Swelling-Activated Chloride Currents in Human Atrial Myocytes

Abstract

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.

Noradrenaline up‐regulates volume‐regulated chloride current by PKA‐independent cAMP/exchange protein activated by cAMP pathway in human atrial myocytes

“…Nonetheless, PKC stimulated I Cl.vol in canine atrial myocytes (Du and Sorota, 1999) and mouse ventricular myocytes (Gong et al, 2004). Similarly, a recent report demonstrated that I Cl.vol was increased by 100 μM phenylephrine via activation of α 1 -adrenoceptor and PKC in human atrial myocytes (Li and Du, 2015). The present study demonstrated that I Cl.vol up-regulation by noradrenaline was not affected by blocking α 1 -adrenoceptors with prazosin.…”

“…To determine whether noradrenaline-augmented I Cl.vol was due to α 1 -adrenoceptor activation, as observed with a high concentration of phenylephrine (Li and Du, 2015), the α 1 -adrenoceptor antagonist prazosin (2 μM) was applied during cell swelling in 0.6 T solution. Figure 2A shows the time course of I Cl.vol recorded with a ramp protocol (as in Figure 1A).…”

“…The α 1 -adrenoceptor agonist phenylephrine and noradrenaline were reported to inhibit I Cl.vol by activating PKC in rabbit atrial myocytes (Duan et al, 1995). However, a recent report demonstrated that I Cl.vol is increased by phenylephrine via activating PKC in human atrial myocytes (Li and Du, 2015). Regulation of cardiac I Cl.vol by β-adrenoceptormediated cAMP/PKA is also inconsistent.…”