Avtor/Urednik		Sikdar, Sujit K; Kreft, Marko; Zorec, Robert
Naslov		Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs
Tip		članek
Vir		J Physiol (Lond)
Vol. in št.		Letnik 511, št. 3
Leto izdaje		1998
Obseg		str. 851-9
Jezik		eng
Abstrakt		1. Secretory responses were measured in single rat pituatary melanotrophs as the relative increase in membrane capacitance (Cm) 8 min after the start of dialysis with solutions containing 0.45 micro Ca2+. In the added presence of cAMP (0.2 mM) in the patch pipette solution, capacitance responses increased 2- to 3-fold in comparison with controls. 2. To study whether cAMP-dependent mechanisms affect cytosolic calcium activity ((Ca2+)i), dibutyryl cyclic AMP (dbcAMP, 10 mM) was added to intact melanotrophs and (Ca2+)1 was measured using fura-2 AM. Addition of dbcAMP caused a transient reduction in (Ca2+)i to 82+- 21 nM from a resting value of 100+- 19 nM (mean += S.E.M., n = 32, P < 0.001), indicating that the cAMP-induced increase in secretory activity was not the result of cAMP acting to increase (Ca2+)i, which then increased secretory activity. 3. To investigate whether cAMP affects the secretory apparatus diretly, the interaction of a single secretory granule with the plasmalemma was monitored by measuring discrete femtofarad steps in Cm. The signal-to-noise ratio of recordings was incrased by preincubating the cells with a hydrophobic anion, dipicrylamine. 4. Recordings of unitary exocytic events (discrete 'on' steps in Cm) showed that the amplitude of 'on' steps - a parameter correlated to the size of exocytosing secretory granules - increased from 4.2 +_ 0.2 fF (n = 356) in controls to 7.9 +- 0.2 fF in the presence of cAMP (n = 329, P < 0.001), while the frequency of unitary exocytic events was similar in controls and in the presence of cAMP. 5. The results suggest that a cAMP-dependent mechanism mediates the fusion of larger granules with the plasmalemma.
Deskriptorji		PITUITARY GLAND CYCLIC AMP EXOCYTOSIS BUCLADESINE CALCIUM CYTOSOL MELANOPHORES RATS, WISTAR PATCH-CLAMP TECHNIQUES ADENOSINE TRIPHOSPHATE CELL MEMBRANE ELECTRIC CONDUCTIVITY