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Calcium homeostasis in identified rat gonadotrophs.
Author(s) -
Tse A,
Tse F W,
Hille B
Publication year - 1994
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1994.sp020212
Subject(s) - cyclopiazonic acid , intracellular , thapsigargin , extracellular , chemistry , biophysics , homeostasis , gonadotropic cell , depolarization , cytoplasm , calcium , endocrinology , medicine , biology , biochemistry , hormone , pituitary gland , organic chemistry
1. Whole‐cell voltage clamp was used in conjunction with the fluorescent Ca2+ indicator indo‐1 to measure extracellular Ca2+ entry and intracellular Ca2+ concentrations ([Ca2+]i) in rat gonadotrophs identified with the reverse haemolytic plaque assay. 2. Depolarizations to potentials more positive than ‐40 mV elicited inward Ca2+ current (ICa) and transient elevations of [Ca2+]i. 3. The relationship between [Ca2+]i elevations and Ca2+ entry with different Ca2+ buffer concentrations in the pipette showed that endogenous Ca2+ buffers normally bind approximately 99% of the Ca2+ entering the cell. 4. With [Ca2+]i elevations less than 500 nM, decay of [Ca2+]i could be approximated by an exponential whose time constant increased with the concentration of exogenous Ca2+ buffers. 5. Inhibitors of intracellular Ca(2+)‐ATPases, thapsigargin, cyclopiazonic acid (CPA) and 2,5‐di‐(tert‐butyl)‐1,4‐benzohydroquinone (BHQ), caused [Ca2+]i to rise. Application of BHQ during [Ca2+]i oscillations induced by gonadotrophin‐releasing hormone (GnRH) terminated the oscillation in a slowly decaying elevation. BHQ slowed the decay of depolarization‐induced [Ca2+]i elevations about 3‐fold. 6. Taking into account the Ca2+ buffering properties of the cytoplasm permitted estimation of the fluxes and rate constants for Ca2+ movements in gonadotrophs. The intracellular store is a major determinant of Ca2+ homeostasis in gonadotrophs.