1. Endocytosis following exocytosis evoked by single step depolarizations was examined in @entity291 adrenal chromaffin cells using high resolution capacitance measurements in perforated-patch voltage clamp recordings. 2. Endocytosis was detected as a smooth exponential decline in membrane capacitance to either the pre-stimulus level ('compensatory retrieval') or far below the pre-stimulus level ('excess retrieval'). During excess retrieval, > 10% of the cell surface could be internalized in under 5 s. 3. Compensatory retrieval was equal in magnitude to stimulus-evoked exocytosis for membrane additions > 100 fF (about fifty large dense-cored vesicles). In contrast, excess retrieval surpassed both the stimulus-evoked exocytosis, and the initial capacitance level recorded at the onset of phase-tracking measurements. Cell capacitance was not maintained at the level achieved by excess retrieval but slowly returned to pre-stimulus levels, even in the absence of stimulation. 4. A large percentage of capacitance increases < 100 fF, usually evoked by 40 ms depolarizations, were not accompanied by membrane retrieval. 5. Compensatory retrieval could occur with any amount of @entity141 entry, but excess retrieval was never triggered below a threshold @entity141 current integral of 70 pC. 6. The kinetics of compensatory and excess retrieval differed by an order of magnitude. Compensatory retrieval was usually fitted with a single exponential function that had a median time constant of 5.7 s. Excess retrieval usually occurred with double exponential kinetics that had an extremely fast first time constant (median, 670 ms) and a second time constant indistinguishable from that of compensatory retrieval. 7. The speed of compensatory retrieval was @entity141 dependent: the largest mono-exponential time constants occurred for the smallest amounts of @entity141 entry and decreased with increasing @entity141 entry. The @entity141 dependence of mono-exponential time constants was disrupted by @entity205 ( @entity870 ), an inhibitor of the @entity141 - and calmodulin-dependent phosphatase calcineurin. 8. CsA also reduced the proportion of responses with excess retrieval, but this action was caused by a shift in @entity141 entry values below the threshold for activation. The lower total @entity141 entry in the presence of CsA was due to an increase in the rate of @entity141 current inactivation rather than a reduction in peak amplitude. 9. Our data suggest that compensatory and excess retrieval represent two independent, @entity141 -regulated mechanisms of rapid membrane internalization in @entity291 adrenal chromaffin cells. Alternatively, there is a single membrane internalization mechanism that can switch between two distinct modes of behaviour.

Compensatory and excess retrieval: two types of endocytosis following single step depolarizations in XXXX adrenal chromaffin cells.

@entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca2+', 'Ca(2+)'] @entity205 :: ('MESH:D016572', 'Chemical') :: ['cyclosporin A'] @entity291 :: ('9913', 'Species') :: ['bovine'] @entity870 :: ('CHEBI:55379', 'Chemical') :: ['CsA']
@entity291 :: (9913,Species) :: ['bovine']
