HORMONAL-REGULATION OF POTASSIUM CURRENTS IN SINGLE MYOMETRIAL CELLS

Three potassium currents (I(K)) were recorded from myometrial cells isolated from the uterus of rats at estrus and diestrus and kept in culture for 1-6 days. I(K) were differentiated by their modulation with norepinephrine and/or by their onset kinetics. At +50 mV the activation time constants were about 0.7 ms, 6 ms, and 15 ms for the fast, the intermediate, and the slow I(K), respectively. Norepinephrine (1 μM) potentiated the fast I(K) and reduced the intermediate I(K). In addition, differences were found with respect to cells from animals at estrus and diestrus. The fast I(K) was preferentially expressed in cultures from animals at estrus, whereas the intermediate I(K) was more frequent in cells from rats at diestrus. These results indicate that K+ channels from myometrial cells are multiregulated. Regulation may occur by short-term signals (neurotransmitters) and/or by preferentially expressing distinct types of channels depending on the hormonal status of the animal.