ISSN:
1432-1424
Keywords:
Amino acid transport
;
ATP regulation
;
Beta
;
Mg2+
;
pH
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Macroscopic instantaneous and time-dependent currents have been measured in the vacuolar membrane of Beta vulgaris using a patch clamp configuration analogous to whole cell mode. At low cytosolic Ca2+ and in the absence of Mg2+, only an instantaneous current was observed. This current is carried predominantly by cations (PK∶PCl 7∶1, pna∶pcl 4∶1 and arginine is also conducted). The instantaneous current can be activated by ATP4− (e.g., ATP-activated mean K+ current density was −20 mA.m−2 at a membrane voltage of −20 mV) and by increasing cytosolic pH and Mg2+ (raising Mg2+ from 0 to 0.4 mm induced a mean current density increase of −7 mA.m−2 at −20 mV). Such current can be activated by simultaneous addition of putative in vivo concentrations of ATP4−/MgATP/Mg free 2+ (in the presence of bafilomycin to inhibit the vacuolar ATPase) and further modulated by cytosolic pH. With vacuolar K+ concentration greater than that of the cytosol, activation of the instantaneous current would mediate vacuolar K+ release over the range of physiological membrane voltage. It is argued that the ATP4−-activated current, in addition to acting as a K+ mobilization pathway, could provide a counter-ion (shunt) conductance, allowing the two electrogenic H+ pumps which reside in the vacuolar membrane to acidify the vacuolar lumen. A separate time-dependent current, which was not observed at low Ca2+ concentrations (less than 500 nm) could also be elicited by addition of Mg2+ at the cytoplasmic membrane face. This current was stimulated by increasing cytoplasmic pH.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00233308
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