Agonist-induced changes in cell membrane capacitance and conductance in dialysed pancreatic acinar cells of rats.
1. Single acinar cells enzymatically isolated from the rat pancreas were subjected to tight-seal whole-cell recordings. Changes in cell membrane capacitance and conductance were simultaneously recorded using a phase-sensitive detection method. 2. Acetylcholine (ACh, 0.05-0.5 microM) and cholecystokinin octapeptide (CCK-8, 10-50 pM) concomitantly induced transient increases in cell membrane current, capacitance and conductance only when cytosolic Ca2+ was weakly chelated by EGTA (70 microM). These responses were prolonged when the cells were dialysed with a solution containing GTP gamma S (a stable analogue of GTP, 50-100 microM), whereas they were inhibited by dialysing with that containing GDP beta S (a stable analogue of GDP). These results suggest that a type of guanine-nucleotide-binding protein (G-protein) could be involved in ACh- or CCK-receptor signalling. 3. The ACh- or CCK-induced responses (with or without GTP gamma S in the cytosol) were all abolished when a high dose of EGTA (1-2 mM) was injected into the acinar cells. In addition, A23187, a calcium ionophore, induced sustained responses when the cytosolic Ca2+ was weakly buffered by 70 microM-EGTA. These results suggest that the secretagogues regulate the changes in cell membrane capacitance and conductance via an increase and decrease of cytosolic Ca2+ concentration. 4. Oscillatory changes in cell membrane conductance and capacitance were consistently observed even without applying secretagogues when the cells were dialysed with a solution containing GTP gamma S (50-100 microM) and cytosolic free Ca2+ ions weakly buffered at about 10(-6) M with a low dose of EGTA and CaCl2. 5. The peak amplitude of changes in cell membrane capacitance induced by ACh or CCK-8, with or without GTP gamma S in the cytosol, varied between 200 and 1000 fF, thereby suggesting that 20-100 zymogen granules can fuse with the luminal cell membrane in response to these agonists in rat exocrine pancreatic acinar cells.
Maruyama
Y
Y
Department of Physiology, Faculty of Medicine, University of Tokyo, Japan.
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology; D004553:Electric Conductivity; D006150:Guanine Nucleotides / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D010179:Pancreas / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D006150:Guanine Nucleotides; D007473:Ion Channels; D000001:Calcimycin; D002766:Cholecystokinin; D000109:Acetylcholine; D002118:Calcium