In rodents, protein kinase A (PKA) phosphorylates AChR subunits, thereby modulating receptor functional properties, in particular desensitization. Since the effects of AChR phosphorylation are strongly dependent on the preparation studied, we here investigate the effect of PKA activation on the function of human recombinant e-AChR-channels, expressed in GH4C1 or HEK cells, or of native g-AChR in cultured human myotubes. Wild type and slow-channel eL269F mutant receptors were considered.

In all experiments, PKA catalytic subunit (10 U/ml or 50 U/ml) was infused into the cells through the patch pipette. ACh-evoked currents and Ca2+ transients were recorded using a variety of applications protocols. Fractional Ca2+ current (Pf; i.e. the percentage of ACh-induced current carried by Ca2+ ions) was measured for e-AChR, as PKA appears to regulate this parameter for NMDA receptor.

PKA infusion has no effect on Pf (8.8± 0.7%, n = 9 for control; 9.5 ±1.0, n=10 for PKA). AChR desensitization was also unaffected in all preparations tested: the decay of ACh-evoked currents (100 mM) was described by single exponentials with similar time constants irrespective of PKA presence. Upon repetitive ACh applications (100 mM for 0.5 s at 1 Hz or 10 mM for 0.5 s at 0.1 Hz), current peak amplitude showed the same decrement with and without PKA.

In conclusion, none of the functional parameters tested was affected by PKA, indicating that human and rodent AChR are differentially modulated by this kinase.