PARTICIPATION OF TRANSIENT-TYPE CA-2+ CHANNELS IN THE SUSTAINED INCREASE OF CA-2+ LEVEL IN GH3 CELLS

Participation of two types of Ca2+ channels (T‐ and L‐types) in the sustained increase of cytosolic‐free Ca2+ concentration ([Ca2+]i) was studied in thyrotropin‐releasing hormone (TRH)‐stimulated clonal GH3 pituitary cells. The effects of Ca2+ channel blockers were analyzed by measuring Ca2+ channel current and [Ca2+]i, using whole‐cell voltage‐clamp and Fura‐2 fluorometry, respectively. Phenytoin (100 μM) and Ni2+ (100 μM) selectively blocked T‐type Ca2+ channels and suppressed the TRH‐induced sustained [Ca2+]i increase in single cells. Synthetic ω‐conotoxin (ω‐CgTX, 2 μM) preferentially blocked L‐type Ca2+ channels, but it did not suppress the TRH‐induced sustained [Ca2+]i increase. The present results suggest that the sustained elevations of [Ca2+]i triggered by TRH may be mediated by T‐type Ca2+ channels in GH3 cells. Copyright © 1990 Wiley‐Liss, Inc.