Potassium channel expression level is dependent on the proliferation state in the GH3 pituitary cell line

Previously, we showed that the peakdensity of the transient outward K⁺ current(I_to) expressed in GH3 cells was different inthe S phase than in other phases of the cell cycle. Using cellsynchronization, we show here that I_to dropsprecisely at the quiescent (G₀ phase)/proliferating transition. This change is not due to a modification in the voltage dependence of I_to, but rather to a modificationin its inactivation kinetics. Molecular determination of K⁺channel subunits showed that I_to required theexpression of Kv1.4, Kv4.1, and Kv4.3. We found that the increase inI_to density during the quiescent state wasaccompanied by an increase in Kv1.4 protein expression, whereas Kv4.3expression remained unchanged. We further demonstrate that the linkbetween I_to expression and cell proliferation isnot mediated by variations in cell excitability. These results providenew evidence for the cell cycle dependence ofI_to expression, which could be relevant inunderstanding the mechanisms leading to pituitary adenomas.