Bretylium-induced voltage-gated sodium current in human lymphocytes

Abstract

Using the whole-cell variation of the patch-clamp technique it has been determined that 0.25–3 mM bretylium tosylate (BT) exerts a repolarizing effect on partially depolarized human lymphocytes. The repolarizing effect was ouabain (40 μM)-sensitive, and was inhibited by the removal of external Na + or by the Na +-channel-blocker amiloride (10–44 μM), but K +-channel-blockers 4-aminopyridine (0.1–5 mM) and quinine (100 μM) had no effect. The drug induced a sodium dependent, amiloride-sensitive transient inward current reaching its maximum value approx. 20–30 s after the administration of BT and lasting for 6–10 min. This current was activated by depolarization within 25 ms at around −42 mV, its inactivation took about 2 s and its reversal potential was + 24 ±5 mV. An increase in the intracellular sodium concentration (1.8–3.2 mM) has been observed upon the addition of BT by monitoring the SBFI fluorescence of the dye-loaded cells. It has been shown that whole-cell K + currents are significantly decreased by BT. The existence of voltage and ligand (BT)-gated sodium channels has been postulated in human lymphocytes. These channels are thought to participate in the initiation of membrane repolarization in human lymphocytes, and thereby influence mitogenic or antigen-induced cell-activation processes.