Fig. 1.

Spontaneous electrical activity and Ca²⁺ signaling in pituitary cells. (A) The resting membrane potential (V_m) and slow depolarization in endocrine pituitary cells are determined by several channels, including classic inward rectifier K⁺ (K_ir), ether-a-go-go-related gene (ERG) and TWIK-related (TREK-1) K⁺-conducting channels, still unidentified Na⁺-conducting background channels (Na_b), and T-type Ca²⁺ channels. Once the threshold for action potential firing is reached, L-type Ca²⁺ channels alone or together with voltage-gated Na⁺ (Na_v) channels generate spiking depolarization. Depending on the cell type, spiking depolarization is followed by a rapid and sharp repolarization (bottom left) or plateau bursting type of electrical activity (bottom right). Interactions between delayed rectifier (DR) and Ca²⁺-activated BK-type K⁺ channels appear to play a major role in determining the pattern of electrical activity. (B) Influence of variable durations of bursting activity on the Ca²⁺ signaling pattern in pituitary cells: experimental records.