Influence of cholesterol on catecholamine release from the fusion pore of large dense core chromaffin granules.
Changes in cellular cholesterol can affect exocytosis, but the influence of cholesterol in fusion pore kinetics is unclear. Using carbon fiber amperometry, we monitored quantal catecholamine release from rat chromaffin cells. To bypass any possible effect of cholesterol perturbation on ion channels or the colocalization of voltage-gated Ca(2+) channels with sites of exocytosis, exocytosis was stimulated via uniform elevation of cytosolic [Ca(2+)] (with whole-cell dialysis of a Ca(2+)-buffered solution). Under this condition, alterations of cellular cholesterol affected neither the mean number of amperometric events triggered per cell nor their quantal size and the kinetics of their main spike (which reflects the rapid release during and after rapid fusion pore dilation). In contrast, the reduction of cellular cholesterol shortened the "prespike foot" signals (which reflect the leakage of catecholamine via a semi-stable fusion pore) and reduced the proportion of "stand-alone foot" signals (which reflect the release via a flickering fusion pore that may close before it dilates significantly), whereas an oversupply of cholesterol had opposite effects. Acute extraction of cholesterol from the cytosol (via whole-cell dialysis of a cholesterol extractor) also shortened the prespike foot signals and reduced the proportion of stand-alone foot signals, but acute extracellular application of cholesterol extractor or "soluble" cholesterol had no effect. Our data raise the possibility that cholesterol molecules, particularly those in the cytoplasmic leaflet, helps to constrain the narrow waistline of a semi-stable fusion pore while it is flickering or before it starts to dilate rapidly.
Department of Pharmacology and Center for Neuroscience, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Nan
N
Wang
Christina
C
Kwan
Xiandi
X
Gong
Elena Posse
EP
de Chaves
Amy
A
Tse
Frederick W
FW
Tse
D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D002784:Cholesterol / Q000502:physiology*; D002837:Chromaffin Granules / Q000145:classification / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D008297:Male; D021962:Membrane Microdomains / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D002395:Catecholamines; D002784:Cholesterol