ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The effect of carbamylcholine (Carb) on the release of22Na+ by excitable microsacs is reversible: Carb does not promote an irreversible lysis of the microsacs. The microsacs form closed vesicles which are more permeable to water than to solutes present in physiological media; their apparent volume is controlled by the osmotic pressure of the medium in which they are equilibrated; they behave like micro-osmometers. In the presence of Carb, the apparent volume of the microsacs does not change: Carb has no significant effect on water permeability. The time course of22Na+ release does not follow a simple exponential law and is fitted by a minimum of three exponentials. The complex kinetics are not due to electrical effects but presumably are caused by an heterogeneity both in size and in nature of the microsacs population. Microsacs at rest are permeable to45Ca+,42K+ and22Na+, and to36Cl− but slightly or not at all to32S−SO −2 4 . In the presence of Carb, the permeability to22Na+,42K+ and45Ca++ increases, whereas the permeability to14C-tetraethylammonium and14C-choline does not change. Carb has no effect on the permeability to negatively charged or uncharged permeants. The kinetics of22Na+ efflux is independent of the total concentration of Na+ either inside or outside the microsacs. The outward transport of Na+ thus varies only with the concentration of ion facing theinside of the membrane. Efflux of42K+ follows the same laws as the efflux of22Na+ except that it is blocked by+Na ions present in the outside medium.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01874113
