A SLOW OUTWARD CURRENT AND A HYPOOSMOLALITY INDUCED ANION CONDUCTANCE IN EMBRYONIC CHICKEN OSTEOCLASTS

Krasznai, Z. and Weidema, F. and Ypey, D. L. and Gáspár, R. and Márián, Teréz and Damjanovich, Sándor (2001) A SLOW OUTWARD CURRENT AND A HYPOOSMOLALITY INDUCED ANION CONDUCTANCE IN EMBRYONIC CHICKEN OSTEOCLASTS. Acta Biologica Hungarica, 52 (1). pp. 47-61. ISSN 0236-5383

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Abstract

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 cur- rent, Islo. 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 acti- vated 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 Ba 2+ (1 mM), blockers of K + conductances in chicken osteoclasts, did not influence Islo. However, Islo was inhibited by 50 mM extracellular verapamil, which allowed us to study Iosmo in isolation. Exposure of the osteoclasts to hypotonic solution resulted in the development of a depolarization acti- vated 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 depolariza- tion and did not inactivate during at least 5 sec. Iosmo reversed around the calculated Nernst potential for C1 Ś (ECl = +7.3 mV and Vrev = +5.4 ± 3.6 mV, n = 9). The underlying conductance, Gosmo exhibited mod- erate outward rectification around 0 mV in symmetrical C1 Ś solutions. Ion substitution experiments showed that Gosmo is an anion conductance with PCl » PF ≯ Pgluc ≯≯ P Na. Iosmo was blocked by 0.5 mM SITS but 50 mM verapamil, 5 mM TEA, 5 mM 4-AP, 1 mM Ba 2+, 50 mM cytochalasin D and 0.5 mM alendronate did not have any effect on the current. Cl Ś currents

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