In this paper we report on a hypoosmolality induced current, Iosmo, in embryonic chicken osteoclasts, which could only be studied when blocking a simultaneously active, unidentified slow outward current, Islo. However Islo was observed in all of the examined cells when both the intracellular and extracellular solutions contained sodium as the major cation and no potassium. The current was outwardly rectifying and activated at membrane potentials more positive than +44 ± 12 mV (n = 31). The time to half activation of the current was also voltage dependent and was 350 ms at Vm = +80 mV, and 78 ms at VM= +120 mV. The current did not inactivate during periods up to 5 s. Extracellular 4-AP (5 mM), TEA (5 mM) and Ba2+ (1 mM), blockers of K+ conductances in chicken osteoclasts, did not influence Islo. However, Islo was inhibited by 50 μM extracellular verapamil, which allowed us to study Iosmo in isolation. Exposure of the osteoclasts to hypotonic solution resulted in the development of a depolarization activated Iosmo. It developed after a 1-min delay and reached its maximum within 10 minutes. Half-maximal activation occurred after 4.4 ± 0.9 min (n = 9). The current activated within a few ms upon depolarization and did not inactivate during at least 5 sec. Iosmo reversed around the calculated Nernst potential for C1-(Ec1 = +7.3 mV and Vrev = +5.4 ± 3.6 m,V n = 9). The underlying conductance, Gosmo exhibited moderate outward rectification around 0 mV in symmetrical Cl- solutions. Ion substitution experiments showed that Gosmo is an anion conductance with Pc1 ≈ PF > Pgluc ≫ PNa· Iosmowas blocked by 0.5 mM SITS but 50 μM verapamil, 5 mM TEA, 5 mM 4-AP, I mM Ba2+, 50 μM cytochalasin D and 0.5 mM alendronate did not have any effect on the current. CI- currents have been implicated in charge neutralization during osteoclastic acid secretion for bone resorption. The present results imply that osmolality may be a factor controlling this charge neutralization.
- Anion conductance
- Bone resorption
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Environmental Science(all)