Membrane currents of myocardial cells in the snail, Helix pomatia L.

Abstract

1. 1. A two microelectrode voltage-clamp method was used to investigate the inward and outward membrane currents of snail ventricular fibres. 2. 2. The presence of a slow Ca-sensitive inward current ( I si) was described. This was activated at - 35 mV and peaked between 0 and + 10 mV. 3. 3. The I-V characteristic of the fully activated outward currents accompanying a 3–5 sec depolarization was N-shaped, indicating the presence of both inward and outward rectification. 4. 4. The time- and voltage-dependent outward current could be resolved into two exponentials when plotted on a semilogarithmic scale. 5. 5. The fast component had a time constant of between 0.5 and 1.2 sec, and this outward current is thought to represent a pacemaker current in a snail heart. The activation variable was 0 at −35 mV and 1 at +45 mV. 6. 6. The time constant of the other component of outward current was found to be between 2.5-4.5 sec. 7. 7. The role of different currents components are discussed.