Effect of ionic environment on oxygen uptake and lactate production of myometrium

The present studies were designed to measure the metabolic cost, in terms of oxygen consumption (QO2) and lactate production, of membrane ion transport, and activation of the contractile apparatus of rat myometrium. The normal QO2 of 16.98 +/- 0.84 mumol/g wet tissue per h was reduced to 15.42 +/- 0.66 in the presence of high-K (127 mM) solution. This was further reduced to 14.05 +/- 0.77 and 13.53 +/- 0.76 by the addition of D-600 (10(-5) M), which inhibits Ca influx or in the presence of Ca-deficient high-K solutions, respectively. Ouabain (10(-3) M) reduced QO2 by an amount similar to that produced by high K. Addition of K+ to Na-rich preparations produced an immediate ouabain-sensitive increase of QO2 whose rate was a linear function of [K+]o up to 30 mM in Ca-deficient solution. In all of the above conditions, changes in lactate release paralleled those in QO2. Isoproterenol (10(-6) M), which causes mechanical inhibition of myometrium, had no effect on the QO2 of muscles in normal solution but reduced the QO2 of muscles in Ca-deficient solution. Lactate release was increased by isoproterenol in both normal and Ca-deficient solutions. These results show that the Na pump is an important site of energy utilization in myometrium. Components which can be interpreted in terms of energy utilization for Ca pumping and the contractile apparatus were also demonstrated.