Current-fluctuation noise in toad urinary bladder during active transport of sodium ions

Abstract

The voltage-fluctuation noise spectrum appearing across the excised urinary bladder of the female Dominican toad Bufo marinus during active transport of sodium is identified as arising from random current fluctuations in the sodium-ion active transport current. The noise is observed to disappear with the sodium-ion active transport blocked when the bladder is bathed in choline Ringer solution. The noise magnitude with the bladder open-circuited and with the bladder short-circuited is proportional to the sodium-ion active transport current. The open-circuit active transport current is taken to be equal to the Ohmic current through the bladder resistance at the resting potential. The short-circuit active transport current is taken to be equal to the external current that must be injected into the bladder to drive the transbladder potential to zero. The bladder resistance is determined from the measurement of the frequency-dependent impedance of the bladder. Interpretation of the voltage-fluctuation spectral density according to the theoretical expressions for current-fluctuation noise indicates that the fluctuations are produced by the correlated movement through the bladder of a large number of sodium ions, carrying approximately 5000 electronic charges in a time of 0.02 sec.