Avtor/Urednik		Rupnik, M
Naslov		Uravnavanje eksocitozne sekrecije pri hipofiznih celicah: vloga kloridnih ionov in GTP-beljakovin
Tip		monografija
Kraj izdaje		Ljubljana
Založnik		Medicinska fakulteta
Leto izdaje		1994
Obseg		str. 35
Jezik		slo
Abstrakt		We use the whole-cell patch-clamp technique to monitor changes in membrane capacitance to study the influence of cytosolic Cl- ions on the secretory activity of single rat melanotrophs. As reported previously, increased cytosolic Ca2+ triggers secretory activity in a dose dependent manner. Apparent KD for Ca2+ was reduced 4-5 times following the increase in cytosolic chloride concentration from 4 mM to 154 mM. Chloride ions were thus suggested to enhance the sensitivity of the secretory machinery to Ca2+. The mechanism of this stimulation is not known, however it may involve GTP binding proteins. It was shown previously that high (Cl-)i stabilizes guanine nucleotides bound to purified catalytic subunit of GTP-binding proteins. In our experiments we were able to modulate the Ca2+ -induced secretory activity using the nonhydrolysable guanosine nucleotide analogues, GTP-gamma-S and GDP-beta-S, which affect GTP binding proteins activity. The effectiveness of the GDP-beta-S was enhanced at 154 mM, which corresponded to its increased binding affinity at higher (Cl-)i. Pertussis toxin caused ADP-ribosylation inhibited Ca2+ -induced secretory response, again only at high (Cl-)i. In the presence of vanishingly low cytosolic Ca2+, the addition of GTP-y-S alone intensifed the secretory activity. The effect of GTP-gamma-S at this low (Ca2+)i was smaller compared to the GTP-gamma-S response in the presence of 1 microM (Ca2+)i. At high (Cl-)i GDP-beta-S inhibited the secretory activity in (Ca2+)i independent fasion. We have proposed that in excitable melanotrophs a Ca2+ -dependent and a Ca2+ -independent secretory pathway coexist. They are possibly coupled in series, the Ca2+ -dependent pathway preceeding the Ca2+ -independent. Considering the effect of nonhydrolysable analogues and the modulatory role for chloride ions, the meeting point of both pathways is a pertussis toxin sensitive, heterotrimeric GTP-binding protein.
Deskriptorji		PITUITARY GLAND PATCH-CLAMP TECHNIQUES CALCIUM CHLORIDES PERTUSSIS TOXINS CELLS, CULTURED RATS ANIMALS, LABORATORY MELANOPHORES GUANOSINE TRIPHOSPATE CYTOSOL EXOCYTOSIS