A method for determination of shunt resistance (Rs) and absolute conductive ion permeabilities of the apical membrane in epithelia from steady-state data is described. The method assumes that the currents are satisfactorily described by the Goldman-Hodgkin-Katz regime. Its application requires measurements of standard transepithelial electrophysiological parameters and of one or more intracellular ion activities. It is applicable under both open- and short-circuit conditions. The method was tested in an electrophysiological analysis of cultured normal and cystic fibrosis (CF) human nasal epithelium. In 15 normal and 10 CF preparations with mean transepithelial resistances of 338 and 427 omega.cm2, Rs was 412 and 623 omega.cm2, respectively. The Rs values determined with the present method were strongly correlated (r = 0.94) with those obtained with another method available in the electrophysiological literature but were as a mean 20% lower. Amiloride increased Rs by 25% in CF and by 8% in normal preparations. In normal preparations, the apical Cl permeability (PCla) was 3.6 x 10(-6) cm/s, and the apical Na permeability (PNaa) was 1.6 x 10(-6) cm/s. In CF preparations, PCla was reduced to a maximum of 2.3 x 10(-7) cm/s, whereas PNaa was increased to 6.2 x 10(-6) cm/s. The apical membrane electromotive force was -1 mV in normal and 43 mV in CF preparations. It is concluded that the method can be used to calculate Rs, apical membrane ion permeabilities, and electromotive forces from steady-state electrophysiological data.
The passive electrical properties of guinea-pig ventricular muscle as examined with a voltage-clamp technique.
