The apical membrane of distal nephron epithelium (A6) has a Ca2+-dependent outwardly rectifying Cl− channel with single channel conductances of 3 pS for outward current and 1 pS for inward current under the basal condition. The single channel conductance for inward currents increased as cytosolic Ca2+ concentration ([Ca2+] c ) was elevated, while the single channel conductance for outward currents did not change at the range of [Ca2+] c from 10 nm to 1 mm. Insulin (100 nm) increased the single channel conductance for the inward current by increasing the sensitivity to cytosolic Ca2+ by 400-fold, but did not affect the single channel conductance for the outward current. Further, insulin increased the open probability of the channel. These effects of insulin were completely blocked by cyclosporin-A, an inhibitor of protein phosphatase type 2B (PP2B) which dephosphorylates phospho-tyrosine in addition to phospho-serine/threonine, but not by okadaic acid, an inhibitor of protein phosphatase type 1 and 2A. Further, these effects of insulin were also completely blocked by W7, an antagonist of calmodulin which is required for activation of PP2B. Lavendustin A, an inhibitor of protein tyrosine kinase (PTK), mimicked these effects of insulin; this action of lavendustin A required 1 hr after its application, while within 30 min after its application lavendustin A had no significant effects on the single channel conductance. On the other hand, lavendustin A blocked the insulin action for a relatively short time period (i.e., within 30 min after their application). However, H89 (an inhibitor of protein kinase A) or H7 (an inhibitor of protein kinases A, C and G) did not mimic the insulin action. Application of PP2B or protein tyrosine phosphatase to the cytosolic surface of the inside-out patch membrane increased the single channel conductance and the open probability as did insulin in cell-attached patches. The insulin-induced increases in single channel conductance and open probability were reversibly decreased by application of PTK catalytic subunit in the presence of ATP through a decrease in the sensitivity to cytosolic Ca2+, but not by protein kinase A. These observations suggest that as intracellular signalling of insulin action, PP2B-mediated dephosphorylation of phospho-tyrosine of the channel protein (or channel-associated protein) is a novel mechanism for regulation of single channel conductance, and that at least two different types of PTKs regulate the channel characteristics.
The Journal of Membrane Biology – Springer Journals
Published: Feb 1, 1998
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera