Potassium accumulation and depletion in frog atrial muscle

Area of Science:

• Cardiac Electrophysiology
• Ion Transport Mechanisms
• Cellular Physiology

Background:

• Slowly decaying membrane currents observed in atrial trabeculae of Rana species following voltage clamp pulses.
• These currents are hypothesized to result from potassium ion accumulation/depletion rather than time-dependent conductance channels.

Purpose of the Study:

• To investigate the role of potassium ion accumulation and depletion in generating slow membrane currents in atrial tissue.
• To develop and validate a model for potassium accumulation effects on ionic currents.

Main Methods:

• Voltage clamp techniques applied to atrial trabeculae of Rana catesbeiana and R. ridibunda.
• Experimental testing of predictions derived from a potassium accumulation model.
• Analysis of time-independent potassium conductance (iK1) and its relation to extracellular potassium concentration ([K]O).

Main Results:

• Evidence presented for potassium ion accumulation in unclamped atrial tissue.
• A simple accumulation model was developed, predicting shifts in reversal potentials for ixfast and ixslow.
• The decay of current tails associated with iK1 was found to be exponential, with a time constant (tauacc) related to accumulation decay.
• Experimental verification of the 'cross-over' effect in iK1(Em) relations, mimicking conductance mechanisms.
• Potassium depletion identified during hyperpolarizing pulses, necessitating consideration in pace-maker current (ixslow) analysis.

Conclusions:

• Potassium ion accumulation and depletion are significant factors influencing membrane currents in frog atrial tissue.
• The developed accumulation model provides a framework for understanding these effects on ionic conductances.
• Findings necessitate re-evaluation of kinetic analyses of atrial ion currents, particularly ixslow.