4-AP hyperpolarizes granulosa cell resting potential and increases intracellular potassium. A) Granulosa cells (GC) were cultured in the basic media, alone (Con), or with 4AP (2 mM), FSH (200 ng/mL) or FSH+4AP. After 24 hours, resting membrane potentials were compared using DiBAC4(3) fluorescence. Decreased DiBAC4(3) fluorescence indicates hyperpolarization of resting membrane potential. Data were obtained from 16 (Con, 4-AP) or 17 (FSH, FSH+4AP) culture wells from 4 GC isolations. B) GC were cultured in the basic media, alone, or with 4AP, FSH or FSH+4AP. After 24 hours, intracellular K+ concentrations were compared by PBFI fluorescence. Increased PBFI fluorescence indicates increased intracellular potassium concentration. Data were obtained from 5 (FSH, FSH+4-AP) or 7 (Con, 4-AP) culture wells from 3 GC isolations. In both panels, asterisk indicates P < 0.05 compared with GC cultured under similar conditions in the absence of 4-AP.