Kinetics of calciumdependent inactivation of calcium current in voltageclamped neurones of Aplysia californica
Chad, J., Eckert, R. and Ewald, D. (1984) Kinetics of calciumdependent inactivation of calcium current in voltageclamped neurones of Aplysia californica Journal of Physiology, 347, (1), pp. 279300.
Download
Full text not available from this repository.
Description/Abstract
Ca currents flowing during voltageclamp depolarizations were examined in axotomized Aplysia neurones under conditions that virtually eliminated other currents. Moderate to large currents exhibited a twocomponent time course of relaxation that can be approximated reasonably well by the sum of two exponentials. The rapid phase (tau 1 approximately equal to 70 ms at 0 mV) plus the slower phase (tau 2 approximately equal to 300 ms at 0 mV) ride upon a steady, noninactivating current, I infinity. Conditions that diminish the peak current amplitude, such as reduced stimulus depolarization, inactivation remaining from a prior depolarization, or partial blockade of the Ca conductance by Cd, slowed both phases of inactivation, and all selectively eliminated the tau 1 phase, such that weak currents exhibited only the slower phase of decline. Injection of EGTA slowed both phases of inactivation, decreased the extent of the tau 1 phase, and increased the intensity of I infinity and of the current during the tau 2 phase. For a given voltage, the rate of inactivation increased as the peak current strength was increased, and decreased as the peak current strength was decreased. For a given peak current the rate of inactivation decreased as depolarization was increased. The relation of inactivation to prior Ca2+ entry was essentially linear for small currents, but decreased in slope with time during strong currents. The relation also became shallower with increasing depolarization, suggesting an apparent decrease in the efficacy of Ca in causing inactivation at more positive potentials. The basic kinetics of Ca current inactivation along with experimentally induced changes in those kinetics were simulated with a bindingsite model in which inactivation develops during current flow as a function of the entry and accumulation of free Ca2+. This demonstrated that a single Camediated process can account for the twocomponent time course of inactivation, and that the nearly biexponential shape need not arise from two separate processes. The twocomponent time course emerges as a consequence of a postulated hyperbolic reaction between diminishing probability of channels remaining open and the accumulation of intracellular free Ca2+. The occurrence of a single or a twocomponent time course of inactivation thus appears to depend on the levels of internal free Ca2+ traversed during current flow.
Item Type:  Article  

ISSNs:  00223751 (print) 

Related URLs:  
Subjects:  
ePrint ID:  55974  
Date : 


Date Deposited:  22 Aug 2008  
Last Modified:  16 Apr 2017 17:42  
Further Information:  Google Scholar  
URI:  http://eprints.soton.ac.uk/id/eprint/55974 
Actions (login required)
View Item 