| Description |
Voltage-gated potassium channels are important regulators of neuronal excitability, determining resting potentials, repolarizing action potentials and modulating sensory plasticity. In mammalian olfactory receptor neurons (ORNs), odor stimulated excitation is modulated by voltage-gated ion channels including potassium channels. In this study, ORNs from adult Swiss-Webster mice were acutely dissociated and cultured them in vitro. Depending on culture conditions, a relatively large inactivating potassium current (I A ) and relatively small noninactivating potassium current were present in adult mouse ORNs. Pharmacologically, the inactivating component was blocked by 4-aminopyridine (4-AP) and a peptide blocker rAa1. RT-PCR, immunohistochemical and immunoblot studies showed that I A of mouse ORNs contained the Kv1.4, Kv4.2 and Kv4.3 subunits, which belong to the A-type subfamily of voltage-gated potassium channels. Interestingly, in long term cell culture, the I A was downregulated by prosurvival peptide PACAP in parallel with a reduction in caspase activity. The reduction in caspase activity was mimicked by blocking I A with 4-AP, suggesting an important role of I A in cell apoptosis and survival. The reduction of I A by PACAP depended on the PLC intracellular signaling pathway and involved both a downregulation of genetic expression (Kv1.4 and Kv4.2 but not Kv4.3) and a direct functional modulation of the channels. In addition, calcium imaging showed that selectively blocking I A with the peptide blocker rAa1 prolonged the calcium response in ORNs, thus I A can be regarded as a temporal modulator. However, blocking I A with 4-AP unexpectedly reduced the calcium response probably due to initiation of a calcium-dependent feedback inhibition. These observations suggest that I A plays both physiological and pathophysiological roles in olfactory system, that reduction of I A is a crucial mechanism for the anti-apoptotic effect of PACAP, and that different I A antagonists may have contrasting biological effects. |
