OSMOLAR CHANGES REGULATE THE PARACELLULAR PERMEABILITY OF CULTURED HUMAN CERVICAL EPITHELIUM

Extracellular nucleotides induce a biphasic change in the transepithel ial electrical conductance (G(T)) Of human cervical cells grown on fil ters: a rapid increase (phase I) followed by a sustained decrease (pha se II). To probe the involvement of the intercellular space, its magni tude was varied by manipulating cell volume through changes in extrace llular osmolarity. Under baseline conditions [G(T) = 115 mS/ cm(2) (si milar to 9 Omega . cm(2))] and during phase II, hypertonic challenges resulted in an increase in G(T) (0.98%. mosmol(-1). l(-1) and 0.73%. m osmol(-1). l(-1), respectively). However, a hypertonic challenge durin g phase I decreased G(T) -(0.16%. mosmol(-1). l-1). Hypotonic challeng es decreased GT during baseline, phase I, and phase II conditions by - 1%. mosmol(-1). l(-1). Similar trends were observed with regard to py ranine permeability. Reduction of extracellular calcium increased G(T) , abrogated the phase II effect of extracellular ATP, and reversed the effect of a hypertonic challenge. The additive nature of the permeabi lity changes in response to osmotic challenges and to ATP during phase II suggests that different sites are involved in each response, i.e., the resistance of the intercellular space changes with osmolarity and that of the tight junction during phase II.