Evidence for activation of BK _Ca channels by a known inhibitor of focal adhesion kinase, PF573228

Aims PF573228 is an inhibitor of focal adhesion kinase (FAK) and recognized to affect cell adhesion and migration in many types of cells. Its effects on ion currents and membrane potential have been investigated in this study. Main method Electrophysiological studies of PF573228 actions on ion currents were performed in pituitary tumor (GH ₃) cells, in GH ₃ cells transfected with K _Ca1.1 siRNAs and in human embryonic kidney (HEK) cells expressing α-human slowpoke (α-hSlo). Key findings In whole-cell experiments, PF573228 reversibly increased the amplitude of Ca ²⁺-activated K ⁺ currents (I _K(Ca)) in GH ₃ cells. In inside-out recordings, this compound added to the bath did not modify single-channel conductance but stimulated large-conductance Ca ²⁺-activated K ⁺ (BK _Ca) channels with an EC ₅₀ value of 3.2 μM. As BK _Ca-channel activity was stimulated by PF573228 (3 μM), subsequent application of BMS191011 (3 μM) did not further increase channel activity. PF573228 shifted the activation curve of BK _Ca channels to less positive membrane potential. Change in the kinetic behavior of BK _Ca channels caused by this compound is a result of the increased backward rate constants between closed states. PF573228 depressed the firing of action potentials in GH ₃ cells. However, in GH ₃ cells transfected with K _Ca1.1 siRNAs, PF573228-stimulated I _K(Ca) was abolished. In HEK293T cells expressing α-hSlo, PF573228 enhanced BK _Ca-channel activity. Significance In addition to an inhibition of FAK phosphorylation, PF573228 is effective in activating BK _Ca channels. The direct stimulation of these channels by this compound may contribute to the underlying mechanism through which it influences cell behavior.