Electrophysiological responses to somatostatin of rat hypophysial cells in somatotroph-enriched primary cultures.
1. Somatotroph cells were obtained from pituitaries of adult male rats by dissociation, separation and enrichment on a continuous gradient of bovine serum albumin at unit gravity. They were kept in culture for 7-15 days before electrophysiological experiments. 2. Immunofluorescent staining of the resulting gradient fractions (numbered F2 to F9) indicated that the majority of somatotrophs (75-85%) were located in the heavy fractions (F8 and F9). However, a small percentage (15-20%) of cells in these fractions were identified as lactotrophs. 3. Perifusion experiments indicated that on the one hand release of growth hormone from somatotroph-enriched fractions was stable at the level of 6 ng (2 min)-1 (10(6) cells)-1 and was markedly inhibited by somatostatin (1.9 ng (2 min)-1 (10(6) cells)-1) but not by dopamine. On the other hand, in the same cell preparations, basal prolactin release (1.6 ng (2 min)-1 (10(6) cells)-1) was significantly reduced by dopamine (0.08 ng (2 min)-1 (10(6) cells)-1) but remained unchanged by somatostatin treatment. 4. The inhibitory effect of somatostatin on growth hormone release was dose dependent. This effect was not abolished by tetraethylammonium (40 mM) or 4-aminopyridine (5 mM), but somatostatin decreased high-potassium-induced release. 5. In all the cells recorded (n = 187), 14% (n = 26) displayed a low resting potential (less than -30 mV) and poor membrane resistance (less than 50 M omega). The recording was unstable and resting potentials decreased regularly to 0 mV in less than 5 min. The other 86% of the cells displayed resting potentials varying from -45 to -65 mV and had a membrane resistance of more than 150 M omega. Only cells which displayed these membrane characteristics showed clear responses to somatostatin or dopamine, and were therefore chosen for experiments. 6. In all the cells selected for the experiments (n = 161), 78% (n = 126) showed either triggered or spontaneous action potentials. The action potentials remained insensitive to sodium-free bath solution, but were reversibly blocked by the calcium channel blockers cobalt (5 mM) or nickel (5 mM). 7. When the cells were at resting potential, somatostatin induced a hyperpolarizing response associated with a decrease of membrane resistance. During this response, spontaneous or triggered action potentials were inhibited. The hyperpolarizing response induced by somatostatin was dose-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)
Chen
C
C
Laboratoire de Neurobiologie des Comportements INSERM-U. 176, Bordeaux, France.
Israel
J M
JM
Vincent
J D
JD
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010902:Pituitary Gland / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D013757:Tetraethylammonium Compounds; D013004:Somatostatin; D011388:Prolactin; D013006:Growth Hormone; D011188:Potassium; D004298:Dopamine