Decrease in intracellular Zn²⁺ level by propranolol : A model experiment using rat thymocytes

Propranolol is a representative β-blocker used for the treatment of cardiovascular diseases. Because the use
of propranolol expands for some clinical purposes that are not related to its β-blocking action, it is necessary to
further examine cellular actions of propranolol. We revealed that propranolol decreased the intracellular Zn2+
level in rat thymocytes by the use of cytometric technique with FluoZin-3, a fluorescent indicator of intracellular
Zn2+. Propranolol decreased the influx of extracellular Zn2+. However, the agent decreased the intracellular
Zn2+ level even in the presence of DTPA, a chelator of extracellular Zn2+. Thus, the decrease in intracellular
Zn2+ level by propranolol was not due to the decrease in Zn2+ influx by propranolol. Propranolol increased the
cellular content of nonprotein thiol that was estimated by the use of 5-chloromethylfluorescein fluorescence, an
indicator for non-proteinous thiol. Since non-proteinous thiols can make a complex with Zn2+, propranolol may
increase the cellular content of nonprotein thiol, resulting in the decrease in intracellular Zn2+ level. Since the
concentrations of propranolol to affect both intracellular Zn2+ level and cellular content of nonprotein thiol are
higher than those reported under clinical conditions, it is difficult to emphasize clinical implications from present
results.