Electrophysiology of Necturus urinary bladder: I. "Instantaneous" current-voltage relations in the presence of varying mucosal sodium concentrations

The "instantaneous" transepithelial current-voltage (I-V) relations of Necturus urinary bladder were determined. The findings indicate that: While the rate of active Na transport (I sub(sc)) increases hyperbolically with increasing (Na) sub(m), (Na) sub(c) is maintained constant. The increase in I sub(sc) with increasing (Na) sub(m) is entirely attributable to an increase in sub(0)G sub(N)um sub(a); P sub(N)um sub(a) decreases with increasing (Na) sub(m). A possible mechanism that could acount for both the increase in basolateral pump activity in the face of a constant (Na) sub(c) and the increase in g super(s) that parallels the increase in pump activity is the "recruitment" of additional "pump-leak units" to the basolateral membrane with increasing (Na) sub(m).