Author/Editor		Rupnik, M; Zorec, R
Title		Intracellular Cl- modulates Ca2+-induced exocytosis from rat melanotrophs through GTP-binding proteins
Type		članek
Source		Pflugers Arch
Vol. and No.		Letnik 431, št. 1
Publication year		1995
Volume		str. 76-83
Language		eng
Abstract		We used the whole-cell patch-clamp technique to monitor changes in membrane capacitance (Cm) to study the influence of cytosolic concentration ((C1-)i) on the secretory activity of rat melanotrophs. The sensitivity of the secretory machinery to Ca2+ was enhanced in the presence of a high (C1-)i. The free concentration of Ca2+ required for half-maximal secretory activity was reduced from 3.2 microM at 4 mM (c1-)i to 0.7 microM at 154 mM (C1-)i. To study whether the modulation of secretory activity by C1- involves guanosine 5'-triphosphate-(GTP-) binding proteins, cells were dialysed with non-hydrolysable GTP and GDP analogues, fluoroaluminate (A1F4-), or were pretreated with pertussis toxin. With guanosine 5'-0-(3-thiotriphosphate) (GTP(gama-S), 100 microM) the maximal rate of Cm increase (dCm/dt) was enhanced at 4 and 14 mM (c1-)i, but it was not affected at 154 mM (C1-)i. In contrast, the secretory response, measured as a percentage of resting Cm 10 min after the start of recordings, was reduced at 154 mM (C1-)i, but not affected at 4 mM (C1-)i. Only with 154 mM (C1-)i did intracellular dialysis of cells with guanosine 5'-0-(2-thiodiphosphate) (GDP(beta-S), 500 microM) inhibit dCm/dt as well as relative secretory responses. The presence of AIF4- (30 microM) or a 7-h pretreatment of cells with pertussis toxin (250 ng/ml) significantly reduced both the maximal dCm/dt and relative secretory responses, but only in the presence of 154 mM (C1-)i. Since the effects of GDP-(beta-S), A1F4-, and pertussis toxin pretreatment were only detected with a high (C1-)i, we conclude that modulation by C1- of secretory activity of rat melanotrophs is mediated through GTP-binding proteins. Furthermore, the effects of A1F4- and pertussis toxin indicate a role of heterotrimeric GTP-binding proteins in the secretory activity of melanotrophs.
Descriptors		CHLORINE CALCIUM EXOCYTOSIS G-PROTEINS PERTUSSIS TOXINS RATS PATCH-CLAMP TECHNIQUES ION TRANSPORT SECRETORY RATE PITUITARY GLAND, ANTERIOR