Time course of active Na transport and oxidative metabolism following transepithelial potential perturbation in toad urinary bladder

Summary The use of an Ussing chamber with well-defined mixing characteristics coupled to a mass spectrometer permits the concurrent evaluation of transepithelial current and oxidative metabolism with improved temporal resolution. The time-course of the amiloride-sensitive currentI^a and the rate of suprabasal CO₂ productionJ_CO2^sb were observed in 10 toad urinary bladders at short-circuit and after clamping at 100 mV, serosa positive. Following perturbation of (0100mV),I^a declined sharply within 1/2 min, remained near constant 15 min, and then increased slightly.J_CO2^sb declined more gradually, remained near constant at 4–7 min, and then declined further. Detailed analysis revealed an early quasi-steady state with near constancy ofJ_CO2^sb starting at 2.9±1.1 (sd) min and lasting 4.7 ±1.8 (sd) min, followed by relaxation to a later steady state at about 15 min. During the early quasi-steady state,I^a was also nearly constant. Considering that in steady statesI^a/FJ_Na^a, the rate of transepithelial active Na transport, during the early quasi-steady state mean values ±se ofJ_Na^a,J_CO2^sb and (J_Na^a/J_CO2^sb) were, respectively, 29.9±1.7%, 59.4 ±3.2%, and 56.4±5.7% of values at short-circuit. Corresponding values during the late steady state were 41.4±6.0%, 38.2±6.1%, and 111.3±8.6%. Thus the flow ratioJ_Na^a/J_CO2^sb was depressed significantly during the early quasi-steady state, but returned later to the original value. The results of measurements ofI^a andJ_CO2^sb in three hemibladders were qualitatively similar. In terms of a phenomenological black-box treatment the findings are consistent with earlier studies indicating incomplete coupling between transport and metabolism. Further studies will be required to clarify the molecular basis for these observations.