Heterogeneity of the Ca2+ sensitivity of secretion in a pituitary gonadotrope cell line and its modulation by protein kinase C and Ca2

• Published in: Journal of cellular physiology 2006-06, Vol.207 (3), p.668-674
• Main Authors: Liu, Hui-Sheng, Hu, Zhi-Tao, Zhou, Ke-Ming, Jiu, Ya-Ming, Yang, Hua, Wu, Zheng-Xing, Xu, Tao
• Format: Article
• Language: English
• Subjects: Animals; Calcium - chemistry; Calcium - metabolism; Calcium - pharmacology; Cations, Divalent - chemistry; Cell Line; Exocytosis - drug effects; Gonadotropin-Releasing Hormone - pharmacology; Kinetics; Mice; Pituitary Gland - drug effects; Pituitary Gland - enzymology; Pituitary Gland - secretion; Protein Kinase C - metabolism
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.20598

Modulation of the Ca2+ sensitivity and cooperativity of secretion is an important means of regulating neurotransmission and hormone secretion. Employing high‐time resolution measurement of membrane capacitance (Cm) stimulated by step‐like or ramp [Ca2+]i elevation, we have identified the co‐existence of both a high and low Ca2+‐sensitive exocytosis in an immortal pituitary gonadotrope cell line, LβT2. Ramp [Ca2+]i generated by slow uncaging elicited a biphasic Cm response. The first phase of response, which represents a highly Ca2+‐sensitive pool (HCSP) of vesicles, began to secrete at low [Ca2+]i concentration (5 µM) and displayed a steep Ca2+ cooperativity. The co‐existence of vesicle populations with different Ca2+ sensitivities was further confirmed by flash photolysis stimuli. The size of the HCSP was ∼30 fF under resting conditions, but was dramatically increased (∼ threefold) by application of phorbol‐12‐myristate‐13‐acetate (PMA, an activator of protein kinase C). Forskolin (an activator of protein kinase A), however, exerted no significant effect on the size of both HCSP and LCSP. GnRH (gonadotropin releasing hormone) augmented the size of both pools to a larger extent (5‐ and 1.7‐fold increase for HCSP and LCSP, respectively). The heterogeneity of Ca2+ sensitivity from different pools of vesicles and its differential modulation by intracellular signals suggests that LβT2 cells are an ideal model to further unravel the mechanism underlying the modulation of Ca2+‐sensing machineries for exocytosis. J. Cell. Physiol. © 2006 Wiley‐Liss, Inc.