Caveolae act as membrane reserves which limit mechanosensitive I(Cl,swell) channel activation during swelling in the rat ventricular myocyte.
BACKGROUND
Many ion channels are preferentially located in caveolae where compartmentalisation/scaffolding with signal transduction components regulates their activity. Channels that are mechanosensitive may be additionally dependent on caveolar control of the mechanical state of the membrane. Here we test which mechanism underlies caveolar-regulation of the mechanosensitive I(Cl,swell) channel in the adult cardiac myocyte.


RESULTS
Rat ventricular myocytes were exposed to solution of 0.02 tonicity (T; until lysis), 0.64T for 10-15 min (swelling), and/or methyl-beta-cyclodextrin (MBCD; to disrupt caveolae). MBCD and 0.64T swelling reduced the number of caveolae visualised by electron microscopy by 75 and 50% respectively. MBCD stimulated translocation of caveolin 3 from caveolae-enriched buoyant membrane fractions, but both caveolin 1 and 3 remained in buoyant fractions after swelling. I(Cl,swell) inhibition in control cells decreased time to half-maximal volume (t(0.5,vol); 0.64T), consistent with a role for I(Cl,swell) in volume regulation. MBCD-treated cells showed reduced time to lysis (0.02T) and t(0.5,vol) (0.64T) compared with controls. The negative inotropic response to swelling (an index of I(Cl,swell) activation) was enhanced by MBCD.


CONCLUSIONS
These data show that disrupting caveolae removes essential membrane reserves, which speeds swelling in hyposmotic conditions, and thereby promotes activation of I(Cl,swell). They illustrate a general principle whereby caveolae as a membrane reserve limit increases in membrane tension during stretch/swelling thereby restricting mechanosensitive channel activation.
Kozera
Lukasz
L
Institute of Membrane and Systems Biology, University of Leeds, Leeds, United Kingdom.
White
Ed
E
Calaghan
Sarah
S
D000818:Animals; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051242:Caveolin 1 / Q000378:metabolism; D051244:Caveolin 3 / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D018118:Chloride Channels / Q000378:metabolism*; D002784:Cholesterol / Q000172:deficiency; D006352:Heart Ventricles / Q000166:cytology*; D007038:Hypotonic Solutions / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009995:Osmosis / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013499:Surface Properties / Q000187:drug effects; D013997:Time Factors; D047392:beta-Cyclodextrins / Q000494:pharmacology
D051242:Caveolin 1; D051244:Caveolin 3; D018118:Chloride Channels; D007038:Hypotonic Solutions; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol