Dual modulation of chloride conductance by nucleotides in pancreatic and parotid zymogen granules.
The regulation of Cl- conductance by cytoplasmic nucleotides was investigated in pancreatic and parotid zymogen granules. Cl- conductance was assayed by measuring the rate of cation-ionophore-induced osmotic lysis of granules suspended in iso-osmotic salt solutions. Both inhibition and stimulation were observed, depending on the type and concentration of nucleotide. Under optimal conditions, the average inhibition measured in different preparations was 1.6-fold, whereas the average stimulation was 4.4-fold. ATP was inhibitory at 1-10 microM but stimulated Cl- conductance above 50 microM. Stimulation by ATP was more pronounced in granules with low endogenous Cl- conductance. The potency of nucleotides in terms of inhibition was ATP greater than adenosine 5'-[gamma-thio]triphosphate (ATP[S]) greater than UTP much greater than or equal to CTP much greater than or equal to GTP much greater than or equal to guanosine 5'-[gamma-thio]triphosphate (GTP[S]) much greater than or equal to ITP. The potency with respect to stimulation had the following order: adenosine 5'-[beta gamma-methylene]triphosphate (App[CH2]p) greater than ATP greater than guanosine 5'-[beta-thio]diphosphate (GDP[S]). Adenosine 5'-[beta gamma-imido]triphosphate (App[NH]p) was also stimulatory, and was more potent than ATP in the parotid granules, but less potent in the pancreatic granules. Aluminium fluoride stimulated Cl- conductance maximally at 15-30 microM-Al3+ and 10-15 mM-F. F was less effective at higher concentrations. Protein phosphorylation by kinases was apparently not involved, since the nucleotide effects (1) could be mimicked by non-hydrolysable analogues of ATP and GTP, (2) showed reversibility, and (3) were not abolished by the protein kinase inhibitors 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (H-7) or staurosporine. The data suggest the presence of at least two binding sites for nucleotides, whereby occupancy of one induces inhibition and occupancy of the other induces stimulation.
Thévenod
F
F
Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106.
Gasser
K W
KW
Hopfer
U
U
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009928:Organ Specificity; D010179:Pancreas / Q000378:metabolism*; D010306:Parotid Gland / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012265:Ribonucleotides / Q000494:pharmacology*
D002712:Chlorides; D012265:Ribonucleotides; D000255:Adenosine Triphosphate