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Limitations of Voltage Qamp Studies of Slow Inward Current Using the Double Sucrose Gap

Abstract : The electrical behavior of a preparation (single fiber or trabecula) voltage-clamped in a double sucrose gap was checked experimentally on a frog atrial trabecula or using computer simulations. Experimental alterations in isolation factors, maximal inward conductance and series resistance induced unexpected variations in the reversal potential V rev and maximal conductance Gs of slow inward current. Two models were used to examine the conditions required to measure most accurately V tev and G,. The first model accounted only for longitudinal non-uniformity whereas the second took into account both longitudinal and radial non-uniformities. The two models were compared. With thin preparations a classical single unidimensional model was sufficient to describe the electrical behavior of the preparation. Radial non-uniformity became significant only for preparations with a radius larger than 40 \xm. The addition of a diffuse series resistance to the unidimensional model made it applicable to simulate radial non-uniformity of thicker preparations. The unidimensional model was chosen for simulations which revealed several sources of error in the estimation of V rev and G,. A poor sucrose isolation and the non-uniformity of potential in the test gap appeared most significant; both induce an overestimate of G, and an underestimate of V rev. These effects can be countered by moderate increases in the series resistance. Furthermore, decreases in slow inward conductance were associated with reductions in the apparent V rev. Variations in the electrical characteristics of the preparation (leak membrane resistance, internal resistances in the different gaps, etc.) can also yield apparent alterations in G, and V re v. Finally experimental conditions were simulated to reproduce the effects of drugs that alter the slow inward current. The results suggest that V rev (or its variations) cannot easily be determined with accuracy using the double sucrose gap method since its measured value may vary up to 15 mV under given ionic conditions.
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  • HAL Id : hal-03619013, version 1

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R Fischmeister, D Mentrard, G Vassort. Limitations of Voltage Qamp Studies of Slow Inward Current Using the Double Sucrose Gap. General Physiology and Biophysics, Rand d Print, 1982, 1 (5), pp.319-348. ⟨hal-03619013⟩

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