ISSN:
1432-1424
Keywords:
Cl− current
;
Hyperpolarization-activated
;
Osmosensitivity
;
Mechanosensitivity
;
Osteoblast
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract During whole-cell recording of rat osteoblastic cells with high-Cl− internal solutions, 10 sec hyperpolarizing jumps from 0 mV induce a slow inward current relaxation, which is shown to be carried by hyperpolarization-activated Cl− channels. This relaxation increases and becomes faster with stronger hyperpolarizations. It is insensitive to Cs+ ions but is blocked in a voltage-dependent manner by 4,4′-diisothiocyanatostilbene-2, 2′-disulfonic acid (DIDS) 1 mm and is reduced by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) 0.1 mm. Cd2+ ions are potent blockers of this current, blocking completely above 300 μm. The amplitude of the Cl− current activated by a given hyperpolarization increases during the first 10–20 min of whole-cell recording. This evolution and the fact that some recently cloned Cl− channels have been reported to be activated both by hyperpolarization and by external hyposmolarity led us to investigate the effects of external osmolarity. Reducing the external osmolarity induces a large Cl− current. However, this hyposmolarity-induced Cl− current and the hyperpolarization-activated Cl− current are shown to be distinct; 1,9-dideoxy forskolin selectively blocks the hyposmolarity-activated current. We show that the hyperpolarization-activated Cl− current is osmosensitive, but in an unusual way: it is reduced by external hyposmolarity and is increased by external hyperosmolarity. Furthermore, these modulations are more pronounced for small hyperpolarizations. The osmosensitivity of the hyperpolarization-activated Cl− current suggests a mechanosensitivity (activation by positive external pressure) that is likely to be physiologically important to bone cells.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00233706
