Voltage-gated and agonist-mediated rises in intracellular Ca2+ in rat clonal pituitary cells (GH3) held under voltage clamp.
1. Intracellular free calcium (Ca2+i) was estimated in single GH3 cells by dual wavelength emission spectrofluorimetry using the Ca2+ indicator dye Indo-1, while cells were held under voltage clamp using patch clamp techniques. 2. Depolarization of cells evoked a transient rise in Ca2+i that increased with increasing duration of depolarization to a peak at about 10 s. 3. Calcium transients showed a bell-shaped dependence on the amplitude of the depolarizing pulse. They were abolished in the absence of extracellular calcium and by application of 10 microM-nifedipine. 4. Thyrotrophin-releasing hormone (TRH) evoked a transient rise in Ca2+i that was followed by a more sustained period of elevated Ca2+i in some cells. The transient phase of the response but not the sustained phase was seen in the absence of extracellular calcium. 5. Ca2+i transients evoked by depolarization were not affected by pre-release of internal Ca2+ stores with TRH. 6. The results demonstrate that voltage-gated Ca2+ entry and Ca2+ store release can each elevate cytoplasmic free calcium in GH3 cells and may both be important for stimulus-secretion coupling. Non-voltage-gated Ca2+ entry is not a major source of Ca2+ under these conditions.
Benham
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Department of Pharmacology, Smith Kline & French Research Ltd, Welwyn, Herts.
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D002999:Clone Cells; D005456:Fluorescent Dyes; D007211:Indoles; D015640:Ion Channel Gating / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D013997:Time Factors
D005456:Fluorescent Dyes; D007211:Indoles; D013973:Thyrotropin-Releasing Hormone; D009543:Nifedipine; C048960:indo-1; D011188:Potassium; D002118:Calcium