Capacitance increases of dissociated tilapia prolactin cells in response to hyposmotic and depolarizing stimuli

► Secretion from Tilapia prolactin cells was followed as membrane capacitance (Cm) increase by perforated patch clamping. ► Depolarizing pulses stimulated Cm increases (ave 7.2 fF/s, n = 50) and were reversibly blocked by 0 Ca2+ or Cd2+, not by TTX. ► Cm increases in hyposmotic perfusate were much slower (ave 0.68 fF/s, n = 17). ► Hyposmotic responses were reduced by Ca2+-free but not by Cd2+ saline. ► PRL cells secrete hormone using two distinct mechanisms; both are mediated by Ca2+.