Influence of Hepes- and CO2/HCO(3-)-buffer on Ca2+ transients induced by TRH and elevated K+ in rat pituitary GH4C1 cells.
The influence of two buffer systems (Hepes and CO2/HCO3-) on intracellular Ca2+ ([Ca2+]i) transients evoked by TRH and by elevated K+ were studied in single, and small clusters of, clonal rat pituitary GH4C1 cells using Fura 2. The steady-state level of [Ca2+]i was virtually identical in Hepes and CO2/HCO3-. In both buffers, addition of TRH induced a transient increase in [Ca2+]i which attained a significantly higher peak in Hepes (357 +/- 43 nM) when compared with values measured in the presence of CO2/HCO3- (184 +/- 21 nM). In Hepes, the basal IP3-level was higher than in CO2/HCO3-. The TRH-evoked increase in IP3 was higher in magnitude in Hepes than in CO2/HCO3-, although the stimulated/basal ratio was not different between the two buffers. The buffer composition had no effect on the specific binding of 3H-TRH to the cells. Furthermore, the amplitude of the increase in [Ca2+]i evoked by 50 mM K+ was identical in both buffers. TRH and K+ had no effect on pHi in either buffer. The present results indicate that HCO3- has an influence on TRH-induced Ca2+ transient, at least in part by modifying the TRH-evoked production of IP3.
Törnquist
K
K
Department of Biosciences, University of Helsinki, Finland.
Päällysaho
J
J
Heinonen
E
E
Kaila
K
K
D000818:Animals; D001639:Bicarbonates; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide; D002460:Cell Line; D006531:HEPES; D006863:Hydrogen-Ion Concentration; D007295:Inositol Phosphates / Q000378:metabolism; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology
D001639:Bicarbonates; D002021:Buffers; D007295:Inositol Phosphates; D002245:Carbon Dioxide; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D011188:Potassium; D006531:HEPES; D002118:Calcium