Xenopus Oocytes Injected with Rat Uterine RNA Express Very Slowly Activating Potassium Currents

Abstract

Under the influence of estrogen, uterine smooth muscle becomes highly excitable, generating spontaneous and prolonged bursts of action potentials. In a study of the mechanisms by which this transition in excitability occurs, polyadenylated RNA from the uteri of estrogen-treated rats was injected into Xenopus oocytes. The injected oocytes expressed a novel voltage-dependent potassium current. This current was not observed in oocytes injected with RNA from several other excitable tissues, including rat brain and uterine smooth muscle from ovariectomized rats not treated with estrogen. The activation of this current on depolarization was exceptionally slow, particularly for depolarizations from relatively negative membrane potentials. Such a slowly activating channel may play an important role in the slow, repetitive bursts of action potentials in the myometrium.

Cloning and expression of the delayed-rectifier IsK channel from neonatal rat heart and diethylstilbestrol-primed rat uterus.

“…The reversal potential of the tail currents changed 52 mV per 10-fold change in external K+ concentration (n = 6, r = 0.986; data not shown). These results suggest that the current is carried largely by K+ as has been reported for the currents expressed from the kidney LsK cDNA (10) and from uterine mRNA (12).…”

“…(12,13). Both of these currents also bear a strong resemblance to the classical delayed outward rectifier (IV,), the main repolarizing K+ conductance in the cardiac ventricle (14, 15).…”

“…This channel, the IsK protein (11), is structurally unrelated to any ion channel previously described. When expressed by microinjection of RNA into Xenopus oocytes, it induces a slow, voltagedependent K+ current that closely resembles the delayedrectifier K+ current expressed from uterine poly(A)+ mRNA isolated from ovariectomized, diethylstilbestrol (DES)-treated rats (12,13). Both of these currents also bear a strong resemblance to the classical delayed outward rectifier (IV,), the main repolarizing K+ conductance in the cardiac ventricle (14,15).…”

Hormonal regulation of potassium currents in single myometrial cells.

“…In our experiments we have not used long pulses to study the late current (11). This late current has been recorded in Xenopus oocytes injected with uterine mRNA from rats treated with ,B-estradiol (19).…”

Stoichiometry of the cardiac I Ks complex

“…To zap as many spots as possible, Plant et al photobleach the cardiac I Ks complex expressed in mammalian cells instead of the traditional Xenopus oocytes. This switch also avoided the endogenous xKCNQ and xKCNE subunits that are responsible for both the discovery of the KCNE1 subunit (12) and much of the confusion that permeates the cardiac I Ks field.…”