Influence of Cell Isolation and Recording Technique on the Voltage Dependence of the Fast Cardiac Sodium Current of the Rat

We measured macroscopic sodium currents (INa) in preparations from adult rat ventricle under four different conditions (I-IV): using the cell attached configuration of the tight-seal patch clamp technique on cells isolated with either trypsin followed by collagenase (I) or with collagenase only (II), and using the loose patch technique on cells isolated with collagenase (II) as well as on multicellular preparations not subjected to enzyme treatment (IV). The voltage dependence of the steady-state activation of INa as well as of the steady-state inactivation differed significantly among condition I and II. Moreover, the recordings were voltage shifted in comparison to the recording condition III and IV. The potentials of half maximal activation and inactivation were: condition I: -57 ± 8.5 mV (activation, n = 11), -106.8 ± 9.2 mV (inactivation, n = 34) condition II: -49.1 ± 6.9 mV (activation, n = 10), -101.1 ± 7.0 mV (inactivation, n = 15) condition III: -37.9 ± 8.7 mV (activation, n = 12), -79.0 ± 14.1 mV (inactivation, n = 6) condition IV: -39.4 ± 4.0 mV (activation, n = 12), -79.2 ± 7.0 mV (inactivation, n = 16) The shift of inactivation was time dependent and continued after 3-5 min after the seal formation in condition I, but not condition II. No time dependent shift was found in III and IV. We conclude, that the voltage dependence of cardiac sodium current is shifted by gigaseal patch recording. The degree of this shift depends on the type of enzymatic isolation procedure, with trypsin causing more pronounced effects than collagenase. The cell isolation itself seems not to interfere with the voltage dependence of INa, since loose patch recording from multicellular preparations and from single cells isolated with collengenase show no obvious differences.