D. Erlij et al., EFFECT OF INSULIN ON AREA AND NA-CELLS( CHANNEL DENSITY OF APICAL MEMBRANE OF CULTURED TOAD KIDNEY), Journal of physiology, 481(3), 1994, pp. 533-542
1. The stimulation of transepithelial Na+ transport caused by insulin
in A6 cultured toad kidney cells was investigated by determination of
membrane capacitance (C-m), short circuit current (I-sc) and current f
luctuation analysis. Values of C-m are proportional to membrane area w
hile blocker-induced current fluctuation analysis provides an estimate
of the number of active amiloride-sensitive Na+ channels in the apica
l membrane. 2. Insulin simultaneously increased C-m, I-sc and C-t (tra
nsepithelial conductance) in epithelia incubated with Na+-containing s
olutions on both sides. 3. Analysis of 6-chloro-3,5-diaminopyrazine-2-
carboxamide (CDPC)-induced noise showed that insulin increased the num
ber of active Na+ channels in the apical membrane, without altering th
e single channel current. 4. When nystatin was used to permeabilize th
e apical membrane the impedance data revealed the presence of a second
time constant. Analysis of these data indicated that the basolateral
membrane capacitance (C-b) is much larger than the apical membrane cap
acitance (C-a). Insulin administered to nystatin-treated epithelia inc
reased the values for both capacitances. 5. We suggest that the stimul
ation of transepithelial Na+ transport caused by insulin may be associ
ated with the exocytotic delivery of transporters to the apical membra
ne.