PGE2 Activation of Apical Membrane Cl− Channels in A6 Epithelia: Impedance Analysis

AbstractMeasurements of transepithelial electrical impedance of continuously short-circuited A6 epithelia were made at audio frequencies (0.244Hz to 10.45kHz) to investigate the time course and extent to which prostaglandin E2 (PGE2) modulates Cl− transport and apical membrane capacitance in this cell-cultured model epithelium. Apical and basolateral membrane resistances were determined by nonlinear curve-fitting of the impedance vectors at relatively low frequencies (<50Hz) to equations (Păunescu, T. G., and S. I. Helman. 2001. Biophys. J. 81:838–851) where depressed Nyquist impedance semicircles were characteristic of the membrane impedances under control Na+-transporting and amiloride-inhibited conditions. In all tissues (control, amiloride-blocked, and amiloride-blocked and furosemide-pretreated), PGE2 caused relatively small (<∼3μA/cm2) and rapid (<60s) maximal increase of chloride current due to activation of a rather large increase of apical membrane conductance that preceded significant activation of Na+ transport through amiloride-sensitive epithelial Na+ channels (ENaCs). Apical membrane capacitance was frequency-dependent with a Cole-Cole dielectric dispersion whose relaxation frequency was near 150Hz. Analysis of the time-dependent changes of the complex frequency-dependent equivalent capacitance of the cells at frequencies >1.5kHz revealed that the mean 9.8% increase of capacitance caused by PGE2 was not correlated in time with activation of chloride conductance, but rather correlated with activation of apical membrane Na+ transport