The effects of cilostazol, a dual inhibitor of type 3 phosphodiesterase and adenosine uptake, on ion currents were investigated in pituitary GH 3 cells and pheochromocytoma PC12 cells. In whole-cell configuration, cilostazol (10 μM) reversibly increased the amplitude of Ca 2+-activated K+ current [IK(Ca)]-Cilostazol- induced increase in IK(Ca) was suppressed by paxilline (1 μM) but not glibenclamide (10 μM), dequalinium dichloride (10 μM), or β-bungarotoxin (200 nM). Pretreatment of adenosine deaminase (1 U/ml) or α,β-methylene-ADP (100 μM) for 5 h did not alter the magnitude of cilostazol-stimulated IK(Ca). Cilostazol (30 μM) slightly suppressed voltage-dependent L-type Ca2+ current. In inside-out configuration, bath application of cilostazol (10 μM) into intracellular surface caused no change in single-channel conductance; however, it did increase the activity of large-conductance Ca2+-activated K + (BKca) channels. Cilostazol enhanced the channel activity in a concentration-dependent manner with an EC50 value of 3.5 μM. Cilostazol (10 μM) shifted the activation curve of BK Ca channels to less positive membrane potentials. Changes in the kinetic behavior of BKCa channels caused by cilostazol were related to an increase in mean open time and a decrease in mean closed time. Under current-clamp configuration, cilostazol decreased the firing frequency of action potentials. In pheochromocytoma PC12 cells, cilostazol (10 μM) also increased IK(Ca) channel activity. Cilostazol-mediated stimulation of IK(Ca) appeared to be not linked to its inhibition of adenosine uptake or phosphodiesterase. The channel-stimulating properties of cilostazol may, at least in part, contribute to the underlying mechanisms by which it affects neuroendocrine function.
All Science Journal Classification (ASJC) codes