The effect of raised pH on pacemaker activity and ionic currents in cardiac purkinje fibers |
| |
Authors: | Pierre-Paul van Bogaert Johan S. Vereecke Edward E. Carmeliet |
| |
Affiliation: | 1. Laboratorium voor Fysiologie, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerpen, Belgium 2. Laboratorium voor Fysiologie, Campus Gasthuisberg, Universiteit Leuven, Herestraat, B-3000, Leuven, Belgium
|
| |
Abstract: | - Cardiac Purkinje fibers exposed to alkaline solutions (pH 8 to 9.5) show an increase in rate of diastolic depolarization, eventually resulting in induction of spontaneous activity or an increase of the spontaneous firing rate.
- The voltage-clamp analysis of the transmembrane currents in pH 9–9.5 shows: i) a shift in the depolarizing direction of the activation (s∞) and time constants (τ s ) curve of the (i_{{text{K}}_{text{2}} }) current, ii) a small increase in the maximal value of the fully activated (i_{{text{K}}_{text{2}} }) current, iii) no significant change of background current in the pacemaker region of membrane potentials.
- The effect of NH4Cl was studied as a means to vary intracellular pH. In the presence of Tris buffer the addition of 5 mM NH4Cl resulted in i) a shift in the depolarizing direction and a decrease in slope of the activation curve of the (i_{{text{K}}_{text{2}} }) current, ii) a shift in the depolarizing direction of the time-constants curve together with an increase in the maximum value of τ s , iii) an increase in the maximum value of the fully activated (i_{{text{K}}_{text{2}} }) current and a depolarizing shift of the reversal potential, similar to the effect of addition of Kc. In the presence of CO2?HCO3 buffer the addition of NH4Cl had no significant effect on the kinetics of the (i_{{text{K}}_{text{2}} }) current. Since intracellular pH is only affected by NH4Cl in the presence of Tris buffer, the results suggest that intracellular alkalinization is responsible for the change in (i_{{text{K}}_{text{2}} }) kinetics.
- Based on the findings with NH4Cl it is suggested that perfusion with Tris buffered alkaline solutions not only affects net negative surface charges on the outside but also and to a larger extent increases negative surface charges on the inside of the cell membrane.
|
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|