Phasic Oscillations of Extracellular Potassium (Ko) in Pregnant Rat Myometrium

Abstract

K-sensitive microelectrodes were used to measure K+ within the extracellular space (Ko) of pregnant rat myometrium. Contractile activity was monitored by measuring either force or bioelectrical signals. Single and double-barreled electrodes were used. Double-barreled electrodes allowed monitoring of electrical activity 15 microns from the site of Ko measurement. From double-barreled electrode experiments, the bioelectrical burst started first, and then Ko began to rise 0.6 ± 0.1 seconds later. This delay indicates that K+ leaves the cells in response to local electrical activity rather than vice versa. Four control experiments were performed to assess the influence of electrical artifacts caused by tissue motion on Ko values. When observed, artifacts were negative and transient, and hence would result in an underestimation of Ko rises. Artifacts were minimized when tissue motion was minimized by fixing the tissue at both ends. At 37°C, 7 single barreled experiments and 45 contractions were analyzed. Resting Ko was within 1 mM of bath K+ (5 mM) at the beginning and end of the experiments. Ko rose during the contraction, fell after the completion of the contraction, and normalized before the next contraction began. Peak Ko values observed during force production were 18.8 ± 5.9 mM, a value high enough to modulate tissue-level electrical activity. Ko required 15.7 ± 2.8 seconds to normalize halfway (t50). Six experiments expressing 38 contractions were performed at 24°C. The contraction period was longer at 24°C. Values for peak Ko (26.2 ± 9.9 mM) and t50 (29.8±16.2 sec) were both larger than at 37°C (p<0.0003 for both). The direct relationships between peak Ko, t50 and the contraction period, suggest elevations in Ko may modulate contraction frequency. The myometrial interstitial space appears to be functionally important, and Ko metabolism may participate in cell-cell interactions. © 2013 Young, Goloman.