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

R Fischmeister (1) , D Mentrard (2, 3, 4) , G Vassort (2, 3, 4)

1 CARPAT (UMRS1180) - Signalisation et physiopathologie cardiovasculaire
2 INSERM - Institut National de la Santé et de la Recherche Médicale
3 CNRS - Centre National de la Recherche Scientifique
4 UP11 - Université Paris-Sud - Paris 11

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.

Mots clés: Voltage clamp; Sucrose gap method; Cardiac muscle; Calcium current; Computer simulation

Domaines: Cardiologie et système cardiovasculaire; Physiologie [q-bio.TO]

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