| Autor: |
Cantiello, H F, Patenaude, C R, Ausiello, D A |
| Zdroj: |
Journal of Biological Chemistry; December 1989, Vol. 264 Issue: 35 p20867-20870, 4p |
| Abstrakt: |
In nonpolar excitable cells, guanine nucleotide regulatory (G) proteins have been shown to modulate ion channel activity in response to hormone receptor activation. In polarized epithelia, hormone receptor-G protein coupling involved in the generation of cAMP occurs on the basolateral membrane, while the physiological response to this messenger is a stimulation of ion channel activity at the apical membrane. In the present study we have utilized the patch-clamp technique to assess if the polarized renal epithelia, A6, have topologically distinct G proteins at their apical membrane capable of modulating Na+channel activity. In excised inside-out patches of apical membranes, spontaneous Na+channel activity (conductance 8-9 picosiemens) was inhibited by the addition of 0.1 mM guanosine 5‵-O-(2-thio)diphosphate to the cytosolic membrane surface without an effect on single channel conductance. In contrast, the percent open time of spontaneous Na+channels increased from 6 to 50% following the addition of 0.1 mM GTP. The addition of preactivated pertussis toxin (100 ng/ml) to the cytosolic bathing solution of the excised patch inhibited spontaneous Na+channel activity within a minute by 85% from approximately 47 to 7% open time and reduced the percent open time for Na+channel activity to zero after approximately 3 min. The addition of 0.1 mM guanosine 5‵-(3-O-thio)triphosphate or the addition of 20 pM purified human αi-3 subunit to pertussis toxin-treated membrane patches restored Na+channel activity from zero to 35% open time. As little as 0.2 pM αi-3 subunit was capable of restoring Na+channel activity. These data provide evidence for a role of pertussis toxin-sensitive G proteins in the apical plasma membrane of renal epithelia distal to signal transduction pathways in the basolateral membrane of these cells. This raises the possibility of a topologically distinct signal transducing pathway co-localized with the Na+channel. |
| Databáze: |
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