Ro. Arellano et R. Miledi, FUNCTIONAL-ROLE OF FOLLICULAR CELLS IN THE GENERATION OF OSMOLARITY-DEPENDENT CL- CURRENTS IN XENOPUS FOLLICLES, Journal of physiology, 488(2), 1995, pp. 351-357
1. Osmolarity-dependent (osmo-dependent) ionic currents from follicle-
enclosed Xenopus oocytes (follicles) were studied using the two-microe
lectrode voltage-clamp technique, combined with intra-oocyte pressure
injection of sucrose or polyethylene glycols (PEGs). 2. Intra-oocyte i
njections of sucrose or PEG (3-25 nmol) generated inward membrane curr
ents (follicles held at -60 mV) associated with an increase in membran
e conductance. These currents were carried mainly by chloride ions (I-
Cl(osm)), and were strongly attenuated by increasing the tonicity of t
he external medium, or by external application of La3+ (0.1-1 mM). 3.
The ability to generate I-Cl(osm) depended on the molecular weight of
the injected PEG. Injections of PEG 200 or 300 generated I-Cl(osm) in
95% of the follicles tested, PEG 600 generated comparable currents in
only 20% of the follicles, while similar injections of PEG 1000 did no
t elicit I-Cl(osm). 4. Octanol (1-1.5 mM), a gap junction channel bloc
ker, reversibly inhibited 50-90% of the I-Cl(osm) generated by injecti
ons of sucrose or PEG 300. Moreover, sucrose or PEG injections did not
elicit I-Cl(osm) in defolliculated oocytes.5. It is concluded that an
increase in the internal osmolarity of the follicular cells activates
a mechanism, probably involving cellular swelling, which leads to the
opening of I-Cl(osm) channels most probably located in the follicular
cell membrane.