7-Oxo-prostacyclin affects the electrogenic Na+/K+ pump in mouse diaphragm fibers

The effect of a stable prostacyclin derivative, 7-oxo-prostacyclin, on the electrogenic Na+/K+ pump in mouse diaphragm muscle was investigated. Resting membrane potentials of muscle cells were measured with glass microelectrodes. In fresh diaphragm preparations from 7-oxo-prostacyclin-pretreated mice (50 micrograms.kg-1 7-oxo-prostacyclin i.p. 30-34 h prior to the experiment) resting membrane potentials were significantly higher (-83.86 +/- 1.40 mV, mean +/- S.E.M.) than in control preparations (-70.78 +/- 1.07 mV). Ouabain at a concentration of 10(-4) mol.l-1 abolished this hyperpolarization (P < 0.05). The electrogenic effect induced by addition of 5 mmol.l-1 K+ to Na(+)-loaded muscles from 7-oxo-prostacyclin-pretreated animals was also enhanced (delta resting membrane potential = 21.73 +/- 3.13 mV) compared with that of the controls (delta resting membrane potential = 18.36 +/- 1.29 mV). Ouabain antagonized the increase in electrogenicity of Na(+)-loaded diaphragms induced by 7-oxo-prostacyclin pretreatment (P < 0.05). In contrast to control preparations, no inhibition of the electrogenic effect induced by 10 mmol.l-1 Ca2+ ions in Na(+)-loaded muscles was observed in diaphragms from 7-oxo-prostacyclin-pretreated animals. In acute experiments with Na(+)-loaded muscles, where 10(-7) mol.l-1 7-oxo-prostacyclin was added to the bath, resting membrane potential reached up to -100 mV. The electrogenic pump-induced increase in resting membrane potential amounted to approximately 30 mV. This effect could be also abolished by 10(-4) mol.l-1 ouabain (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)