Diacylglycerol modulates action potential frequency in GH3 pituitary cells: correlative biochemical and electrophysiological studies.
We have investigated the involvement of enhanced phosphoinositide metabolism in mediating TRH-induced alteration of electrophysiological events related to prolactin secretion by GH3 cells (a line of pituitary origin). Patch-clamp recording (in the current clamp, whole-cell configuration) showed that a few seconds after TRH application there was a brief period (about 30 s) of membrane hyperpolarization followed by several minutes of increased calcium-dependent action potential frequency. In parallel experiments cells were labeled for 24 h with either [3H]myo-inositol or [3H]arachidonate. Application of TRH resulted in rapid increases in levels of inositol phosphates and diacylglycerol. The time course of elevation of inositol 1,4,5-triphosphate (maximal by 5 s) is compatible with an initial burst of intracellular calcium mobilization associated with a transient phase of TRH-induced prolactin release. Application of TRH was also followed by a rapid but more sustained (several minutes) period of elevated diglyceride accumulation; a time course corresponding to a prolonged period of prolactin release which is dependent on the influx of external calcium. A causal relationship between diglyceride release and increased action potential frequency was demonstrated since local application (via a U-tube apparatus) of either 2 microM phorbol ester (phorbol 12,13-dibutyrate or phorbol 12-myristate 13-acetate) or 60 microM 1-oleoyl-2-acetyl-glycerol to patch-clamped cells could mimic this aspect of the TRH effect. In contrast, the inactive phorbol ester, 4 alpha-phorbol, was unable to elicit this response.(ABSTRACT TRUNCATED AT 250 WORDS)
Gammon
C M
CM
Department of Biochemistry, University of North Carolina, Chapel Hill 27599-7250.
Oxford
G S
GS
Allen
A C
AC
McCarthy
K D
KD
Morell
P
P
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D004075:Diglycerides / Q000378:metabolism* / Q000502:physiology; D005989:Glycerides / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism* / Q000502:physiology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D004075:Diglycerides; D005989:Glycerides; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D013973:Thyrotropin-Releasing Hormone